Download download PDF

Houseplant
Pests and Control
PMC-10073
T
here has been increasing interest and activity in
recent years in utilizing more foliage plants in our
interior living and working environments.
If the indoor environment is properly regulated and
managed to provide optimum growing condition, the
interior plantscape can support a wide variety of plants.
Environmental conditions also have an important influence on the presence, variability and extent of pest
problems. Many interior plants are tropical or subtropical in origin and undergo stress when placed in locations where light, temperature or humidity cannot be
closely regulated.
Plants become more susceptible to insects and diseases,
as well as to abiotic problems, when undergoing environmental stress. Because of conditions that are often
Erwinia stem rot
ideal for pests and the easy transport of the pests with
foliage, the owner or plant maintenance personnel may
encounter many different exotic pest problems.
Identification of the pest is the first step toward an effective pest prevention and/or control program. Once a
positive identification has been made, an Integrated Pest
Management (IPM) program should be developed. The
use of pesticides in interior plantscapes is often difficult because of the lack of registered products and the
proximity to living or working situations. Manipulation
of the environment and the use of biological or physical controls can be very effective if instituted early and
monitored closely.
Photo by Mary Ann Hansen, Virginia Polytechnic Institute
and State University, Bugwood.org
Living plants incorporate beauty, function and a sense
of orderly calm into our homes and offices. Reducing
the impact of pests will insure that they will continue to
add to the quality of our environment.
Contents
Diagnosing problems
Diagnosing problems in the interior plantscape is an important and necessary step in providing complete plant
care. Once you notice a problem, you’ll need to determine its cause before a strategy to remedy the problem
is planned.
Diagnosing problems in the interior plantscape............2
Aphids ..........................................................................4
Fungus gnats . ............................................................. 5
Mealybugs.....................................................................6
Scale insects ............................................................... 7
Whiteflies...................................................................... 8
Spider mites..................................................................9
Thrips...........................................................................10
Cyclamen mite............................................................ 10
Occasional pests . ......................................................11
Grey mold (Botrytis spp.).............................................11
Powdery mildew..........................................................12
Water mold rots ..........................................................13
Pythium.................................................................13
Phythophthora......................................................13
Root and stem rots . ...................................................14
Rhizoctonia...........................................................14
Fusarium...............................................................14
Fungal leaf spots.........................................................15
Acremonium . .......................................................15
Alternaria...............................................................15
Cercospora...........................................................15
Colletotrichum .....................................................15
Gloesporium ........................................................15
Coniothyrium .......................................................15
Curvularia..............................................................15
Fusarium...............................................................16
Helminthosporium . ..............................................16
Leptosphaeria.......................................................16
Systemic bacterial infections .....................................16
Erwinia..................................................................16
Bacterial leaf spots and wilts......................................17
Pseudomonas.......................................................17
Xanthomonas ......................................................17
Virus diseases.............................................................17
Noninfectious, abiotic plant disorders .......................18
Integrated pest management .....................................19
About pesticides ........................................................19
The pesticide label . .............................................19
Pesticide formulations..........................................21
Five steps to safe use of pesticides ....................22
References..................................................................22
Sample label................................................................23
There are different ways you can approach your diagnosis; one is to examine the isolated incident and
determine what insect, mite or disease is causing the
symptom you see. A better way of diagnosing a problem is to look at the entire situation, the environmental
conditions, how and where the pest might have gained
entrance and your own cultural practices. Often, pests
and diseases attack the plant when something else is
affecting and weakening the plant. A close-up view plus
an overall examination will help you determine all of
the problems that are affecting your plant, rather than
just the one you first notice.
Many plant problems exhibit similar symptoms; brown
leaf tips, for example, may be a result of overwatering, yet may also occur when the humidity is too low.
Conversely, several insect and mite problems are very
distinct; whitefly adults, for example, will fly when you
disturb an infested plant, and spider mites leave their
telltale webbing on an infested plant. Sometimes the
symptoms you see indicate several different problems,
none being very specific and all occurring simultaneously. The chart on the following page provides you
with some very general symptoms and their possible
causes, which may help you begin your diagnostic
work. Once you’ve identified some probable causes,
look for specific information on each, and through
a process of elimination, reach your final diagnosis.
Remember to look at the entire plant, examine it very
closely and consider the environmental conditions in
which it exists.
In some cases it may not be possible for you to make
your own diagnosis. You can contact your local Cooperative Extension Service or other specialist for further
assistance in diagnosing your plant problems.
2
Diagnosing Plant Problems: Some General Symptoms and Their Possible Causes
Symptom Possible Causes
Wilting or drooping leaves
Root disease/ill health
Chemical damage
Sucking insects such as mealybugs, scale insects or aphids
Dry soil
Overcrowded roots
Pale green or yellow leaves of all ages Too much light
Insect or mite feeding damage
High temperatures
Nutrient deficiency
Root rot
Pale green or yellow older leaves Nutrient deficiency, especially nitrogen
Poor root health
Too little light
Insect or mite feeding damage
Leaf spots Fungal or bacterial infection
Chemical injury
Overwatering
Sun scorch
Lack of water
Insect feeding damage
Brown or yellow leaf tips Underwatering
Overwatering
Excessively dry soil between waterings
Nutrient toxicity
Excessive soluble salts in the soil
Mechanical injury
Chemical injury
Low humidity
Leaf drop Sudden environmental change (light intensity, temperature,
transplanting, humidity)
Root rot
Poor root health
Leaves are droopy and covered with a shiny, sticky substance or are covered with a dull black mold. Insects may or may not be present. Aphids
Mealy bugs
Scales
Whiteflies
Leaves covered with a grey webbing or are speckled and pale green.
Spider mites
Leaves are silvery green in color with tiny black specks on their surface.
Thrips
Roots are brown and mushy, and their outer covering can be pulled off and separated from the center. Above ground symptoms are varied. Root rot
Poor root health
A toxic solution being poured into the pot
Overwatering
Underwatering
3
Aphids
Aphid damage on aloe vera plant
Description and biology
Aphids are small (1̸16 to 1̸18 inch long), soft-bodied insects
with mouthparts that are made for piercing plant tissue
and sucking the plant’s fluids. Aphids resemble tiny
pears in shape and may be brown, green, red, yellow,
black or some other color. Some aphids secrete a waxy
material that gives them a woolly or cottony appearance. Aphids have long legs and long, slender antennae.
Most species have conicles, two straw-like projections
on the posterior of their bodies. Conicles are unique
to aphids and their presence can be used to distinguish
aphids from other insects. Adult aphids are usually
wingless, but most species also have winged forms
appearing at certain times of the season. Young aphids
resemble smaller, fragile versions of the wingless adults
and may differ slightly in coloration.
Photo by Jeffrey W. Lotz, Florida Department of Agriculture and
Consumer Services, Bugwood.org
Signs and symptoms
Puckered, curled or distorted and discolored leaves
often indicate the presence of aphids. Upon close
examination you may be able to see the aphids themselves as they travel across the leaves or stem of the
plant. Aphids secrete honeydew, a sticky substance
that supports the growth of dark-colored sooty mold.
Its presence on plant surfaces can also indicate aphid
activity. Plants supporting aphid populations generally
appear to be lacking vitality, and new growth is stunted
and disfigured. Some species of aphids feed on parts of
the plant other than the leaves and shoots; one species,
which attacks lettuce, feeds on the plant’s roots and
lives out its life in the soil.
Aphids produce many generations each year. Most
aphids reproduce asexually throughout the year and
the females give birth to live young (parthenogenesis).
The young aphids, or nymphs, shed their skin (molt)
approximately four times before reaching adulthood.
In warm conditions such as the interior plantscape,
aphids can develop from birth into mature adults in
less than two weeks; each adult aphid can produce up
to 100 young per week, resulting in a rapid population
growth under the right conditions. Some aphid species
mate and lay eggs at the end of the summer season, and
these eggs serve as a hardy overwintering stage. The
young nymphs then emerge in the spring. In the interior
plantscape aphids have no need for winter survival,
and the warm, constant atmosphere contributes to their
successful population expansion (or explosions as may
happen on occasion).
Plants that host great numbers of aphids may be killed
as a result of constant aphid feeding. Some species of
aphids transmit viruses, which may be introduced into
the plant when the aphids feed (mostly found in those
species that infest vegetable crops). Certain species
of aphids inject toxins into the plant, which may also
distort the plant’s growth.
Aphids
Prevention and control options
Aphids are fragile insects that can often be dislodged
from the plant with a strong spray of water. Insecticidal
soaps registered for use in the interior plantscape provide good control, especially for spot treatments. There
are several biological control agents that can be used for
successful aphid control, such as the familiar convergent lady beetle, lacewings and the larvae of syrphid (or
hover) flies. Insecticidal chemicals registered for use in
the interior plantscape can effectively control aphids but
may not be necessary if the aphid population is effectively reduced with an initial spray of water.
Photo by Cheryl Moorehead, Seattle, WA
4
Fungus gnats
Adult fungus gnat (Mycetohpilidae)
Description and biology
Fungus gnats are very small, delicate, flying insects
(about ⅛ inch long). What most people see flying
around their interior plantscape or greenhouse and refer
to as a “fungus gnat” may actually be one of several
different kinds of minute flies, most of which feed
on decaying organic debris and fungi. The two families — Sciaridae, the dark-winged fungus gnats, and
Mycetophilidae, the fungus gnats — include the more
common, familiar species of fungus gnats encountered
in the interior plantscape or greenhouse. Fungus gnats
generally breed in leaf litter or other decaying organic
material in the outdoor environment and may find their
way into the home or greenhouse. Once inside, they
breed in houseplant containers or other indoor areas
that contain decaying organic material or fungi.
Photo by Johnny N. Dell, Bugwood.org
Signs and symptoms
Mild infestations of fungus gnats may not yield any
recognizable plant symptoms — usually you’ll notice a
few of the adult gnats flying around you and your plants.
Severe infestations, when larvae have fed extensively on
plant roots or lower stems, will often result in a wilted,
drooping plant. You may see the tiny larvae and their
damage to the plant roots by gently probing and examining the soil surrounding the damaged roots; using a magnifying lens is helpful. Root rots are also more prevalent
in the damaged roots, and you may observe symptoms
of these as well. The presence of fungus gnats may also
be an indication of excessive moisture or organic buildup
in the soil or some other location in the interior environment.
The adult female usually lays her eggs in decaying
plant material or fungi, and these eggs soon hatch, usually within a few days. The slender, legless, white or
opaque larvae have darkened heads and may be seen
moving in the potting soil. The larvae feed on organic
debris, plant roots or the base of the plant stem at the
soil line. Once fully developed, the larvae stop feeding
and pupate in or on the substrate and soon develop into
the adult gnats. Because of their relatively short life
cycle (approximately 12 days for some species) fungus
gnats seem to suddenly appear from nowhere in great
numbers, much to the dismay of plant owners.
Prevention and control options
Control of fungus gnats begins with reducing the moisture content of the infested soil. Less frequent watering
helps dry out their preferred habitats, and emptying
catch basins will also help. Places that collect water or
grow mold and fungi should be cleaned with household
cleaners. Damaged, diseased or decaying plant material
should be removed to decrease the growth of fungi.
Adult dark-winged fungus gnat (Sciaridae)
For houseplants, fungal buildup on the soil surface can
be reduced by scraping off about ¼ inch of the surface
and replacing it with an equal amount of sand, vermiculite or perlite. Good plant care and sanitation is helpful
in deterring fungus gnats from invading your houseplants.
In severe infestations, a pesticide registered for use on
fungus gnats in the interior environment may be applied
according to label directions. A formulation of Bacillus thuringiensis specific for fungus gnat larvae is also
available.
Photo by David Cappaert, Michigan State University, Bugwood.org
5
eydew. If you suspect mealybugs, you should also examine the plant for aphids because the signs and symptoms of activity are similar for both insects. Remember
that certain species of mealybugs may be found on the
roots of plants and that some above-ground symptoms
can indicate a below-ground problem.
Mealybugs
Description and biology
Mealybugs are small (about ⅛ inch), soft-bodied insects
that appear to be covered with a white or grey powdery
or waxy outer layer. They are generally oval and flattened, and many have white, waxy filaments extending out from their bodies. Mealybugs can move about
freely on their host plant but do so very slowly, often
clustering together on plant surfaces as they feed. They
have mouthparts that enable them to suck sap from the
plant’s leaves, shoots, stems and roots. Adult female
mealybugs are wingless and are usually what you see
on the plant; adult male mealybugs are very small and
gnatlike and have a single pair of wings. The males are
also very short-lived and do not feed during their brief
adulthood. The young mealybugs (nymphs) resemble
the females but lack the copious waxy coatings of the
adult females. Nymphs that become males form a mass
of cottony filaments in which they transform into adult
males; those that become females continue to grow and
exude their waxy outer covering until adulthood.
Mealybugs consume plant fluids, which causes the plant
to lose vigor. Plants with mealybug infestations are
often slow growing or have stunted new growth. The
mealybug’s honeydew secretions and subsequent sooty
mold growth result in unattractive plant surfaces. Plants
that have great numbers of mealybugs feeding on them
can be severely stunted or even killed. Some species of
mealybugs can transmit plant viruses or inject toxins
that will cause growth distortions.
Prevention and control options
Individual mealybugs can be removed by rubbing with
a cotton swab dipped in rubbing alcohol or by removing the infested plant parts. There are certain biological
control agents that prey on mealybugs; the Australian
lady beetle is very useful, and there are parasitic wasps
as well. Chemical control includes certain insecticidal
soaps and certain other pesticides that are registered for
use against mealybugs in interior plantscapes.
Mealybugs may produce one or more generations each
year, depending on the species of mealybug and the
environmental conditions. A young mealybug can reach
adulthood within two to eight weeks, depending on
environmental factors such as temperature and humidity. Female mealybugs lay hundreds of yellowish or
orange eggs in cottony egg sacs. Upon hatching, the
young nymphs crawl out of the sac and across the plant
surfaces. The tiny nymphs may also crawl to nearby
plants or may be carried to other plants by air currents.
Mealybugs of all life stages may be present on a plant
at a single time, and this is especially true in the favorable atmosphere of the interior plantscape.
Mealybugs
Signs and symptoms
Drooping, stunted or distorted leaves often indicate the
presence of mealybugs. Close examination, especially
at the point where the leaves attach to the plant, will
usually reveal a cluster of cottony, waxy white mealybugs. Other places to look include the undersides of
leaves, cracks and crevices in stems and other sheltered
places on the plant. Like aphids, mealybugs produce
honeydew when they feed, which in turn provides a
substrate for sooty mold growth. The plant will often
appear to be covered with a brownish or blackish sticky
residue, which is simply sooty mold growth on the hon-
Photo by Peggy Greb, USDA Agricultural Research Service,
Bugwood.org
6
Scale Insects
Wax scales
Green shield scale
Description and biology
Scale insects are sap sucking insects (about 1̸16 to 1̸8 inch
in diameter) that resemble a disclike shield or a rounded
wart or blemish adhering to the plant’s leaves and
stems. Because of their unusual and unexpected physical appearance, scale insects are often unnoticed or
misdiagnosed on the plant. The adult female scales and
many immature scales are immobile and are covered
with a hardened waxy or cottony shell or shield. This
covering can be one of many different shapes, sizes and
colors and is unique to a particular species. The adult
male scales are tiny and gnatlike and are rarely seen
around or on the plant.
Photo by United States National Collection of Scale Insects Photographs Archive, USDA Agricultural Research Service, Bugwood.org
There are two important common groups of scale
insects: the soft scales and the hard, or armored, scales.
The females of both types have the shell-like covering that typifies the uniqueness of all scales. The soft
scales have a covering that can’t be removed from their
body without harming or killing the insect; the armored
scales can be separated from the coverings they’ve
formed after settling onto the plant. Like aphids, the
soft scales produce the shiny, sticky honeydew that
sup­ports the growth of sooty mold. The armored scales
don’t produce honeydew and leave no telltale shiny or
sooty plant surfaces.
parts of infested plants may show signs of water stress.
Drooping or yellowing leaves or branches often indicate
scale activity in that particular area or in a nearby area.
Hard scale insects may be more difficult to notice since
they don’t produce honeydew. Signs of an infestation of
hard scales are generally more symptomatic — the infested plant looks as if it lacks water and vigor overall,
and the plant’s leaves and branches may turn yellow or
brown, droop and eventually die.
In the interior plantscape, scale insects may produce
one to eight or more generations in a single year,
depending on the species and host availability. In a generalized life cycle, the stationary female scales produce
several hundred eggs beneath their protective outer
coverings. These eggs hatch into young scales called
“crawlers,” which soon begin to disperse across the
plant’s surface or are carried by air currents to nearby
plants. The tiny crawlers then settle in one place on the
plant, where they stay and feed for the rest of their adult
life.
Prevention and control options
Because of their protective covering, scale insects can
be difficult to control. You should assess the amount
of damage and attempt to remove the heavily infested
plant parts. Spraying the plant with a strong jet of water
can dislodge the young crawlers. There are predators
and parasites that can be employed to combat scale insects. Metaphycus is a parasitic wasp that attacks scale
insects. Some insecticidal soaps, oil sprays and chemical systemic insecticides are registered for scale insect
control in the interior plantscape. Be sure to read the
label for correct application.
Signs and symptoms
Plants that are infested with soft scale insects are often
covered with sticky honeydew, which in turn provides a
growing medium for sooty mold. The leaves and other
7
Adult sweet potato whitefly
Whiteflies
Description and biology
Whiteflies are very small insects (1̸16 to 1̸10 inch) that
have sucking mouthparts. The adults resemble tiny
white moths. When an infested plant is moved, adult
whiteflies leave the undersides of the leaves and fly into
the air creating a cloudlike effect. Immature whiteflies,
when newly hatched, are mobile, tiny crawlers. After
crawling for a brief period, they molt, losing their legs
and antennae and becoming sedentary and scalelike.
Immature whiteflies in this stationary stage feed by
sucking the plant sap. They consume far more than they
can use and the excess material is excreted as honeydew. Once on the plant surface, the sticky honeydew
serves as a substrate for sooty mold growth.
Photo by W. Billen, Pflanzenbeschaustelle, Weil am Rhein,
Bugwood.org
Whiteflies go through a complete life cycle, including a
pupal stage that occurs following the stationary feeding stage. Specific identification is made by examining
the pupal stage because all adult whiteflies are very
similar in appearance. Most whiteflies breed continually
throughout the year, and many have a wide variety of
host plant preferences. The warm temperatures and usually predator-free environment of the interior plantscape
provide an ideal situation for whiteflies and their activities. One of the most common pest species of whitefly,
the greenhouse whitefly, Trialeurodes vaporariorum, is
frequently found on interior plants as well as in greenhouses. Its short life cycle (21 to 36 days, egg to adult,
depending on temperature) can give rise to a sizable
population in a relatively short time.
Signs and symptoms
The first sign of whitefly activity is most often the
white, mothlike adults flying off the plant when disturbed. The adult whiteflies usually inhabit the underside of the mature leaves and a quick check of these
leaves can startle the whiteflies into flight. Immature
stages and pupae can be found on young, fully expanded leaves. An infested plant may show signs of wilting,
leaf yellowing and reduced growth, or the plant’s leaves
may become brittle and dry. Like aphids, whiteflies also
excrete honeydew, and the plant may be covered with
the shiny, sticky substance (as well as being covered
by sooty mold growing on its surface). Some whiteflies
transmit viruses, though mostly to vegetable crops in
certain areas of the country.
Silverleaf whitefly
Prevention and control options
Photo by Scott Bauer, USDA Agricultural Research Service,
Bugwood.org
Adult whiteflies are often difficult to control because of
their ability to fly. They are attracted to yellow sticky
boards, which can be used to trap the adults as they fly
from the plant. The boards can be purchased or you can
make your own using plywood or masonite, painted
bright yellow and coated with a sticky adhesive such
as Tangle Foot or Stickem (commercially available).
Insecticidal soaps can be used effectively in whitefly
control. A hand-held vacuum is a useful tool for sucking
up the adults. Vacuum the plants in the cool morning
hours so you can catch the whiteflies while they’re still
sluggish (be sure to destroy the whiteflies within the
bag). Chemical control of whiteflies may be considered,
though whiteflies often multiply rapidly and successful
chemical control may require repeat applications and
close monitoring.
8
Spider mites
Two-spotted spider mite
Description and biology
Spider mites are tiny web-spinning mites. They are
usually 1̸20 of an inch or less in length and are difficult to
see without the assistance of a hand lens. To the unaided eye, spider mites look like small, fast-moving, reddish, yellow or greenish colored dots on the surface of
the host plant. Their presence, however, is often first indicated by the characteristic silk webbing the mites produce on infested plant parts. Adult mites have oval bodies and eight legs; female spider mites usually have two
large, dark spots on each side of their bodies, whereas
males do not. Both females and males have pale bristles
covering their bodies and bright red eyespots near the
front of their heads. Young mites resemble the adults,
although the immature mites have only six legs when
they first hatch and lack the darkened body marks common on adult females. Spider mite eggs are round and
semitransparent when they are first laid, becoming more
opaque as they approach maturity.
Photo by Eugene E. Nelson, Bugwood.org
Prevention and control options
Spider mites prefer hot, dry conditions with low humidity levels (unfortunately, some insect pests and plant
diseases favor high humidity). Dusty environmental
conditions can contribute to the success of a spider mite
population, and water-stressed plants can also be very
attractive to the invading mites. Avoiding such conditions while maintaining the health of your plants can
reduce the chances for an infestation of spider mites.
Misting your plants frequently can increase the local
humidity of individual plants and make them less attractive to spider mites.
Spider mites may have several generations within a
single season. In warm, often-dry locations such as the
interior plantscape, they may continually reproduce
year-round, completing a single generation in as little
as one or two weeks. Egg-laying activities and development of adults are influenced by the temperature. In
ideal conditions, each female may produce 100 eggs
or more. This allows the mites to infest a plant very
quickly. The two-spotted spider mite, Tetranychus urticae, is a common pest in interior plantscapes (as well as
in greenhouses) and can be quite destructive to individual plants or entire collections. The mites’ unsightly
webbing and feeding activities contribute to the plant’s
overall decline and poor appearance.
A predatory mite, Phytoseiulus persimilis, is a biological control for spider mites and is commercially available from several sources, as are a few other appropriate predatory species. Predatory mites consume both
the eggs and adults of the two-spotted spider mite, thus
making them effective predators when employed as
directed by the supplier.
Signs and symptoms
Often, the most noticeable sign of a spider mite infestation is the webbing that covers infested plant parts. The
first sign of spider mite activity is generally a spotted
or stippled pattern on the plant’s leaves that occurs
when the mites suck out the cell contents. As the mites
continue to feed, they produce more webbing, which
in turn becomes more noticeable. You can often see the
tiny mites as they scurry across the scaffoldlike webbing. The infested plant’s leaves begin to yellow in
response to the tissue damage and eventually they drop
off. A severe infestation of spider mites often results in
an entire plant becoming so unsightly and unhealthy
that the only recourse you have is to discard it.
Chemicals used to control spider mites include insecticidal soaps (those labeled for use against spider mites
— read the label carefully) or one of several miticides
labeled for use in the interior plantscape against spider mites (make sure your plant is listed on the product label). Insecticidal soaps that are labeled for use
against spider mites may be helpful when used as spot
treatments for localized infestations. You may want to
consider removing any heavily infested plant from the
collection to avoid an outbreak since the spider mites
can multiply very rapidly.
9
umeris, that prey on thrips are available commercially
through several sources. Insecticidal soaps registered
for use against thrips in the interior plantscape can be
used as spot treatments when the need arises. Several
other insecticides that are registered for use in the interior plantscape also list thrips. Be sure to read the label.
Thrips
Description and biology
Thrips are small (1̸ 20 inch or less), slender and elongated insects. The adult female thrips have two pairs
of fringed wings, which they hold flat over their back
when at rest. Young thrips resemble adults but lack the
characteristic fringed wings. Some thrips are predators
of other insects and mites, many are serious plant pests
and yet others are both predaceous and plant feeding. In
the interior plantscape, thrips damage plants by rasping and scraping the plant’s surfaces, leaving brown or
silvery scars on the infested tissues.
Cyclamen mite
Description and biology
The cyclamen mite, Steneotarsonemus pallidus, is
a minute (1̸100 inch) pest of cyclamen, African violet,
strawberry and several other plants. Adult cyclamen
mites are pink to brown in color, but the young mites
are translucent and almost colorless. The mites feed
and lay their eggs on the young, newly developing
leaves at the crown of their host plant Because of the
mite’s tiny size, the easiest way to recognize them is by
recognizing symptoms resulting from their activity. As
the infested leaves begin to grow and expand, damage
becomes apparent; leaf margins are cupped, puckered
or distorted in some way and leaf stems fail to elongate.
Adult females lay 25 to 200 eggs in the plant’s tissue.
The newly hatched immature thrips feed for approximately one week before pupating either on leaves or
in soil, depending on the species. The adults emerge
four to 14 days later and may have several overlapping
generations each year.
Signs and symptoms
Thrips activity is most apparent when the insects have
been feeding and crawling about the plant. White or silvery patches on the leaf surface result from the rasping
and scraping feeding method. Their tiny, black fecal pellets can be found in this damaged area. Thrips are often
fast moving and remain hidden on the leaf or flower, so
your first observation is usually this characteristic silvery surface with tiny black specks. Leaves and flowers
may be distorted as a result of thrips’ feeding actions.
Under ideal conditions, cyclamen mites may complete
an entire generation in as little as two weeks. They can
infest several different host plants and crawl from plant
to plant where leaves touch.
Signs and symptoms
As described above, infested leaves are curled and
malformed when first developing and expanding. They
are often brittle and dwarfed or thickened and cupped.
Flower buds are often deformed or withered and seldom
bloom. Flowers that do open are sometimes streaked
with a darker color.
Prevention and control options
Many thrips species are deterred by high humidities, so
misting your plants may be helpful; unfortunately, some
other insect pests and plant diseases prefer high humidities, too. Predatory mites, such as Amblyseius cuc-
Prevention and control options
Preventing cyclamen mites from entering the interior
plantscape is perhaps the best management tool you
have available. Once the mites become established they
can be very difficult to control. Be sure to purchase
mite-free plants, and quarantine new plants before
introducing them into your existing collections. Lightly
infested plants may be immersed in a 105° to 110°F hot
water bath for 20 minutes to kill the inhabiting mites.
This may also do serious damage to some plants. Introducing predatory mites, which feed on cyclamen mites,
into the interior plantscape may provide adequate control. Plants that are heavily infested should be removed
from the collection and discarded.
Thrips damage
Photo by Whitney Cranshaw, Colorado State University, Bugwood.org
10
Occasional pests
Grey mold (Botrytis spp.)
Occasionally, plants will be attacked by less common
pests, or one that has simply decided that the interior
environment is preferable to its usual outdoor habitat.
An exotic pest occurrence may result when the pest
hitchhikes its way into your home on other plant material, on your clothing or on your pets. In general, most
occasional and unusual pests are merely annoying or
startling and are usually only a temporary problem.
Description and biology
Grey mold, or Botrytis, is a common and familiar plant
disease found on both indoor and outdoor plants. Grey
mold gets its name from the greyish, moldlike appearance of its fruiting bodies, which cover infected plant
tissues. Several species of Botrytis cause grey mold,
and spores of this humidity-loving fungus are thought
to be present in most environments. The fungus lives
through dry conditions as tiny, black, specklike resting
stages called sclerotia. Under humid or wet conditions
the sclerotia germinate to form a grey, cobweb-like
growth called mycelium that quickly produces microscopic grapelike clusters of egg-shaped spores. Soon
after the mycelium grows, the pathogen readily releases
spores and the plant becomes covered with dusty,
greyish-tan masses of conidia, or asexual spores. The
spores are easily dispersed with the slightest air movement, and new infections can start on nearby plants
when there is ample moisture.
Leafhoppers, caterpillars, beetles and leaf miners are
just a few of the kinds of occasionally encountered
insect pests, most of which can be removed by hand or
with a spray of water. Leafhoppers will jump from the
plant when disturbed with a spray of water. Beetles and
caterpillars are most easily removed by hand picking
or scooping them off the plant when you see them.
Leaf miners are best controlled by removing the leaf in
which the immature stage has burrowed.
Slugs and snails occasionally infest indoor plants that
have been temporarily placed outside. Removing them
by hand is the easiest and best way to control both
snails and slugs.
The fungus can attack many different plant tissues,
including flower petals, new succulent growth and, in
particular, wounded, dying or dead tissues. It may also
colonize in stems at points of attachment to stakes or
trellises, or on leaves and stems that are in contact with
a pot rim or the soil surface. The fungus also manufactures enzymes that soften plant cells before they are
actually invaded by the mycelium. This advance attack
allows the fungus to grow more rapidly and increases
its ability to spread. Botrytis can survive in decaying
plant material located in or on the soil surface, and also
as sclerotia.
Centipedes and millipedes can occasionally find their
way into the interior plantscape, or they may come in
on new material. Centipedes prey on insects and are
considered beneficial, although to some people their
appearance in the potting medium is annoying. A teaspoon is useful for transferring them into a container
for release outside. Millipedes feed on decaying organic
debris or sometimes on plant parts, but they are rarely
considered serious pests. Since they are slow moving
they can usually be removed by hand.
Signs and symptoms
Centipede
Initial infections appear as soft, water-soaked brown
or tan spots that may darken with age. It is especially
prevalent on plants and plant parts located in areas of
high humidity or in contact with the soil. The cottony,
cobweb-like growth of the grey mycelium forms over
the infected plant parts and is visible to the unaided
eye. By using a hand lens, you can see the characteristic
grape-like cluster of spores that are supported by tiny
stalks and cover the infected tissue. When the fungus
releases its spores, the greyish-tan masses of conidia appear as dust on the plant surfaces. You may also see the
small, black, specklike sclerotia within the mycelial mat
as the infection progresses. As the disease advances,
initially infected plant parts shrivel and decay, and new
plant tissues with moist surfaces are soon attacked.
Photo by Joseph
Berger, Bugwood.org
Millipede
Photo by Gary Alpert, Harvard University, Bugwood.org
11
The fungus may cover an entire leaf or flower surface,
or it may remain in discrete circular lesions on either
side of the leaf. Under the powdery layer the plant
tissue may remain green while the surrounding tissue
turns yellow. The tissue in spots may become crusty or
scablike, and small black specks called sclerotia may
develop in the grey-white powder. Young leaves and
shoots are particularly susceptible, although all portions of the plant that are above ground can be attacked.
Growing leaves may become twisted and misshapen,
and infected buds often fail to open. Flower buds can
become discolored and dwarfed, and finally die.
Prevention and control options
You can minimize grey mold infection by promoting good air circulation and avoiding water build-up
or pooling on plant surfaces. You should use planting
densities and training techniques that provide maximum
air movement throughout the plant canopy. Keep the
humidity below 85 percent and the temperature above
70°F to discourage the disease from developing in the
interior plantscape.
Overfertilization can contribute to excessive growth of
succulent tissue, which in turn is particularly susceptible to infection. Remove and destroy diseased or dead
plant material to prevent new or continuing infection,
and remove live leaves or branches that contact the soil
surface. When you water, avoid misting or overhead
watering; water the soil and not the foliage, taking
care to avoid splashing the plant. A well-drained soil
mix and a container with drainage holes can reduce
the buildup of excess moisture. Allow the soil to dry
out between waterings and water less often to further
reduce the chances of infection. A fungicide registered
for use in the interior plantscape against Botrytis may
be used according to the label directions.
Prevention and control options
Avoid fertilizer applications that are high in nitrogen,
since the rapidly growing succulent tissue is easily attacked by the fungus. Overfertilization can also increase
the severity of an already present problem. Warm
daytime temperatures followed by cool evening temperatures will also favor the development of powdery
mildew. You should therefore try and maintain an environment with a constant temperature to help prevent
the development of the disease. Spacing your plants to
allow better air circulation can help the entire collection
avoid disease buildup. Some plant varieties are resistant
to powdery mildew and should be considered if they’re
available for you to purchase. Wash the leaves with a
mild detergent water to help combat the disease. Consider using a fungicide registered for use in the interior
plantscape against powdery mildew and consult the
product label for application directions.
Powdery Mildew
Description and biology
Powderymildew (Podosphaera pannosa)
Powdery mildew is one of the oldest known and most
easily recognized plant diseases. The three principal genera that cause powdery mildew are Erysiphe,
Sphaerotheca and Podosphaera. Most powdery mildew
fungi grow as thin layers of mycelium on the surface of
the affected plant part. Spores are the primary means of
dispersal and make up the bulk of the powdery growth.
The spores are produced in characteristic chains, which
you can see using a hand lens. The spores are easily detached and can be wind-blown or water-carried to new
hosts. Given favorable conditions, the spores can germinate in less than two hours, penetrating the leaf tissue
with haustoria (a rootlike structure). The haustoria grow
into the epidermal cells of the leaf and absorb liquids
from the host to be used as food. A new crop of spores
is produced every five to 10 days under ideal conditions
of 97 to 99 percent relative humidity and temperatures
between 57° and 75°F.
Photo by Clemson University, USDA Cooperative Extension
Slide Series, Bugwood.org
12
If the affected area is allowed to dry out, the lesion
will become brown and corky and the disease will fail
to continue its development. If allowed to continue, a
dark sap may ooze from the affected spot, and if a portion of the bark is removed, the inner layer may have
reddish brown streaks on its surface. Roots affected by
Phytophthora become brown and brittle; their growth
is often limited to the top part of the soil container. A
cross section of the infected roots may show that the
central core, or conducting tissue, is yellowish or brown
above the rot lesions. Both woody and nonwoody plants
take on a drought-stressed appearance, including wilted,
discolored or stunted leaves. Plants with poor drainage
are generally the first to exhibit signs of a Phytophthora
infection, and the symptoms often develop first on one
branch or stem, then spread to the rest of the plant.
Severely affected plants die but retain their withered
leaves for some time.
Water mold rots
Description and biology
Pythium and Phytophthora are often called water molds
because they have spores that are adapted to spread by
water. Both organisms are found in almost all native
soils and are common causes of root and stem rots.
Pythium spp.
Pythium is one of several fungi that cause damping-off
disease in seeds or young seedlings. Infected seeds are
killed before they emerge from the soil, and infected
young seedlings appear soft and water soaked at or near
the soil line. The tissues of young stems collapse and
disintegrate, and the seedlings soon fall over. Pythium
induced damping-off disease is most severe at temperatures of 50° to 64°F and is most prolific in wet soils
having a pH above 6.0.
Prevention and control options
Good water management and clean, sterile potting soil
are the two most important tools you have against infection by the water molds Pythium and Phytophthora.
Water your plants only as much as needed and avoid
wetting the leaves and stems. Don’t allow the leaves
and stems to come in contact with the container or soil
surface, and be sure to provide the plants with soil that
has adequate porosity. Pythium control may be aided by
maintaining a low soil pH (less than 5.5), and both diseases are less successful when you don’t over- or underfertilize. Before you purchase new plants, examine them
closely for possible disease and be sure to remove and
destroy all infected plant material. In some situations
a fungicide labeled for use in the interior plantscape
against Pythium or Phytophthora may be of use — be
sure to read the product label for correct timing and use.
Mature plants are susceptible to Pythium root rot, and
generally host plants infected with Pythium show signs
and symptoms that vary according to the susceptibility
of the particular host. Many plant species are susceptible to infection by some species of Pythium. Infected
plants show signs of wilting and leaf yellowing, and the
lower leaves often die. Infected roots appear blackened
and mushy and are easily separated from their outer
covering (cortex). The fungi can live on dead plant and
animal material as saprophytes, and can also act as a
low grade parasite attacking any young, succulent plant
tissue. Plants with only slight susceptibility to infection may exhibit slow growth habits. Pythium root rot
thrives in temperatures of 75° to 85°F and is aided by
wet soils with a pH above 6.0.
Phytophthora spp.
Phytophthora rot affects both woody and nonwoody
plants in both stems and roots. It is capable of living
in the soil for up to five years or longer in its resting
stage, thus enabling the fungi to survive long periods of
drought, cold and lack of food. When a host is nearby
and sufficient water is in the soil, the resting spores
germinate to produce motile spores that penetrate roots
and branches directly; the spores don’t need a wound on
the plant to gain access. In nonwoody plants the infection begins as small, water-soaked lesions on the main
stem of the plant at soil line. As the disease progresses,
the lesions become soft and watery and the stem may
eventually collapse.
Phytophthora blight on African violet
Initial infections on woody plants appear as darkened
areas and rarely extend completely through the stem.
Photo by Department of Plant Pathology Archive, North
Carolina State University, Bugwood.org
13
Sometimes the beige, orange or red fruiting bodies are
visible in the midst of the lesions. When the fungus infects the roots, the plant becomes chlorotic and stunted.
Root and stem rots
Description and biology
Prevention and control options
Much like the water molds, fungi such as Rhizoctonia,
Fusarium and others can cause both root and stem rots.
Rhizoctonia lives in the potting medium, Fusarium
lives on plants, and both are capable of persisting in the
growing medium for several months.
Using disease-free plant materials and good sanitation
practices will help keep root and stem diseases under
control. Water deeply and less frequently; keep the soil
moisture low and avoid wetting the foliage and stems.
Use a sterilized potting mix and make sure that all tools
and containers are clean and sterile before and after
each use. Since Rhizoctonia is a soilborne disease present nearly everywhere, avoid using native soils to avoid
accidental introduction and infection. Wounds allow
some species of Fusarium easier access to the plant,
so handle your plants with care to avoid injuring them.
Remove and destroy all infected plant material you find
in the collection to help stop the spread of the diseases.
Certain chemicals may be of limited use in the interior
plantscape for the control of stem and root diseases.
Consult the product label for specific uses and applications.
Rhizoctonia spp.
Species of Rhizoctonia are present in virtually all soils.
The fungi may survive in the soil on dead organic matter, or as spores (or other resting structures), for long
periods of time. The fungus develops best in cool, wet
soils, and studies have indicated that as soil temperature
increases, the growth of the fungus decreases. High
moisture in the potting medium and high humidity
favor the development of the disease.
Rhizoctonia is one of several fungi that are responsible for damping-off, affecting both seeds and young
seedlings (see also water molds: Pythium). Older plants
infected with Rhizoctonia root or stem rot often appear
limp and lacking in vigor. Stem lesions first develop
as water-soaked areas near the soil line and later turn
brown or black, finally girdling the stem. Root rot is
characterized by dark brown, somewhat dry lesions on
the roots and portions of the underground stem. Rhizoctonia can also cause aerial blight and leaf spot, which
appear very different on different plant species.
Fusarium symptoms
Fusarium spp.
Fusarium is a variable fungus composed of many
pathogenic strains and capable of attacking all plant
parts. It is not only responsible for root and stem rots,
but leaf spots and wilts as well. Depending on the species of Fusarium, wounds may or may not be needed
for infection to begin, whereas water is required for
Fusarium leaf spot inoculation. Numerous vectors are
responsible for carrying this pathogen from plant to
plant, including splashing water, human handling and
insect activities.
Stem lesions often start near the soil line and are
generally wet, mushy and sunken with a purple margin
surrounding the infected area. The infection may also
occur on stems that have been cut or pruned. Typically,
a dry rot appears first, becomes mushy and ceases to
progress when it reaches the base of the stem, effectively resulting in the complete loss of the diseased stem.
Photo by Mary Ann Hansen, Virginia Polytechnic Institute and
State University, Bugwood.org
14
Fungal leaf spots
Coniothyrium fungus (leaf spot)
Description and biology
The fungi that cause leaf spots are many. Among the
more common genera are Acremonium, Alternaria, Cercospora, Colletotrichum and Gloesporium, Coniothyrium (the imperfect stage of Leptosphaeria), Curvularia,
Fusarium, Helminthosporium, and Leptosphaeria (the
perfect stage of Coniothyrium). Botrytis, which is another common leaf spotting fungi, has a wide host range
but will only produce spores if the relative humidity
remains high for several hours at a time (see also: grey
mold). Each of these fungi are generally spread from
infected plants by splashing spore-carrying water onto
uninfected plants. Many of these fungi require water
pooling on the plant surface for some time before infection can occur.
Photo by Howard F. Schwartz, Colorado State University,
Bugwood.org
The signs and symptoms of each fungal infection varies
slightly among species and specific identification generally requires laboratory analysis. Fungal diseases often
resemble other plant problems such as over- or underwatering, and without proper identification and control,
they can spread through the collection. The following
information provides some general descriptions of the
fungi mentioned above and how they manifest themselves on an infected plant.
Colletotrichum and Gloesporium spp. The symptoms
of these fungal infections, commonly called anthracnose, can vary widely from one plant species to another.
On some plants the disease may appear as very small
water-soaked lesions on the leaf surface, each spot frequently having a yellowish border. On other plants, the
disease appears as a tip burn with the tips of the leaves
turning first yellow, then tan and finally to dark brown.
Acremonium spp. This fungus causes leaf spots that are
generally circular, having a reddish-brown to yellow
border, and are rarely larger than 1 inch in diameter.
They may be very numerous, giving the leaves a shothole appearance. The infection is generally most severe
on the youngest leaves of the diseased plant.
Coniothyrium spp. The leaf spots of this fungus first
appear as dark brown to black elliptical lesions on the
lower leaves of the infected plant. As the infection
advances, the lesions become depressed and appear
as tan spots with purple margins. Concentric zones of
black and light brown tissue can be seen in mature spots
(some of which reach an inch or more in diameter), and
within the rings you may be able to see the tiny, black
fruiting bodies of the fungus.
Alternaria spp. The leaf lesions of Alternaria first appear as small water-soaked spots that quickly enlarge
to form circular lesions of dead tissue up to 1 inch or
more in diameter. The spots are generally dark brown to
black, and a yellow halo surrounds many of the affected
areas.
Curvularia spp. In the early stages of Curvularia infections, the lesions look like small, greenish ovals and are
generally found on the underside of the leaves. As they
mature, the spots become tan to dark brown, and as the
disease progresses the lesions may coalesce to form
irregular-shaped spots. In severe infections the plant’s
leaves may become distorted and the flowers fail to
open.
Cercospora spp. The leaf spots of this fungi are minute,
sunken or slightly elevated, and are generally found on
the underside of the infected leaves. The lesions may be
tan, brown or purple and are sometimes surrounded by
a halo. Severely infected leaves may have a chlorotic
appearance overall and may drop from the plant prematurely.
15
Fusarium spp. Leaf spots resulting from Fusarium
infection are often in the form of pinpoint-sized, watersoaked spots which develop first on succulent immature
tissue. The spots may later enlarge and become irregular-shaped with a reddish-brown center and yellow
halo. When temperatures are warm and wet, the creamcolored fungal spores may be visible within the infected
area. When the infection is severe, the plant’s entire
new growth becomes involved.
Systemic bacterial infections
Description and biology
Many bacteria, such as Erwinia, are capable of infecting the plant’s vascular tissues and spreading through
the plant. When the pathogens begin to multiply in
specific parts of the plant, they cause stem rots, wilts,
blights and root rots. Stem infections caused by Erwinia
are tan to brown, mushy, water-soaked lesions located
on or near the soil line. A slimy ooze is produced on
some hosts, and in many cases a distinct fetid or sour
odor is present. Leaf infections first appear as pinpointsized, water-soaked spots. As the leaf lesions enlarge,
concentric rings of light and dark tissue are commonly
produced within the affected area. In some hosts,
infection occurs in the whorl (where water is generally
present) and causes a severe blight of the stem and leaf
tissue. Erwinia may also cause a severe root rot, which
results in the wilting and collapse of the entire plant.
Helminthosporium spp. The initial lesions of Helminthosporium are pinpoint-sized chlorotic spots on
young leaves. As the disease progresses, the spots become spindle-shaped or elliptical, and turn tan to black
with a chlorotic yellow-green halo. Older lesions often
develop dark, reddish-brown borders and sometimes
coalesce to form large areas of dead tissue. When a leaf
is infected while still in the sheath, it will blacken and
fail to open.
Leptosphaeria spp. Newly formed lesions are yellow
and water-soaked in appearance, later becoming brown
to greyish in color. The older lesions are pinpoint sized
to about 1 inch in diameter, sometimes with an outer
halo of dark orange-yellow. Leaves that are severely
infected will usually turn yellow and die.
Most bacteria can be spread by splashing water, unsanitary cultural practices or insect feeding activities, and
generally gain entrance into the plant through a wound
of some sort. Since bacteria are carried in and on soil,
plant material and water, they can be fairly widespread
in an interior plantscape as well as a home garden.
Prevention and control options for fungal
leaf spots
Prevention and control options
Many leaf spot fungi require water on the leaf surfaces
for several hours for infection to occur. Water your
plants to avoid splashing the leaves and thereby spreading the fungal spores. Watering early in the day will
give leaves a chance to dry out quickly, and providing
good air circulation will assist the process. Avoid overfertilizing plants since this may result in the production
of excessive succulent growth, which is susceptible
to many fungal diseases. Underfertilizing may cause
the plant to become weak and therefore susceptible to
invasion by an already present plant pathogen. Infected
leaves should be removed and destroyed; the plant may
be aided by occasionally repotting it in well-drained,
pasteurized soil in a clean container. Certain chemicals
may be of use in preventing the spread of some fungal
diseases of interior plants (consult the product label for
applicable use), although in severe infections the best
solution is to remove the diseased plant part or plant
from the collection.
The systemic bacterial infections you may encounter
in your collection can usually be managed simply with
less frequent watering and fertilizing. Avoid splashing
or misting the leaves in order to prevent the transport of
bacteria. Examine each plant for signs of disease before
you purchase them and choose only disease-free material; use sterile potting mixes and containers. Removing
and destroying the infected plant parts may be of use,
though it is important to realize the systemic nature of
these diseases, which means they can spread through
cuttings taken from an infected plant. Chemical applications are ineffective because the pathogen is widely
spread throughout an infected plant.
16
Bacterial leaf spots and wilts
Virus diseases
Description and biology
Virus diseases of interior plants are less common than
diseases caused by fungi or bacteria. Viruses live within
the infected plant’s cells and can spread from cell to cell
unaided. Viruses require physical assistance to spread
from one growing plant to another as well as a wound
through which they gain entrance into the plant. Viruses
are most often spread by insect feeding activities and
cuttings taken from infected material, although they
are also spread less frequently by seed. Insects such as
aphids and leafhoppers are the most important vectors
for transmitting viruses; however, mealybugs, thrips
and whiteflies also transmit viruses. Mites are sometimes vectors (carriers) of viruses, as are some nematodes and soil fungi.
Species of the bacteria Pseudomonas and Xanthomonas
can cause localized leaf spots or blights on plants. Leaf
lesions are initially small, circular or irregular spots,
dark green and water-soaked in appearance. The spots
gradually enlarge, become angular and turn brown to
black. The lesions are sometimes confined to interveinal
areas but may occur anywhere on the leaf blade. Often,
concentric rings of dark and light tissue surround the
lesion, or a yellow or reddish halo encircles the affected
area. Infected plants growing in high moisture conditions may drop their leaves. Xanthomonas may also
cause a vascular infection that causes the entire plant
to wilt even when it is well watered. The infected stem
may show the characteristic browning in the vascular
strands.
Signs and symptoms
The leaves of a plant infected with a viral disease often
provide the first and most noticeable symptom of a viral
infection. The leaves of an infected plant may appear
mottled, with irregular-shaped dark and light green
areas. This variegated color pattern is often referred to
as mosaic. Vein banding, flecking, ring-like spotting
and yellow blotching of the leaves are other common
expressions of viral infection. Occasional growth abnormalities appear that resemble the distortion and damage
caused by misapplication of a herbicide. Infected plants
may be curled, stunted or dwarfed, or generally less
vigorous or more slow growing than uninfected plants.
The bacteria do not require a wound to gain entrance
into the plant; high humidity and temperature favor
development of the bacteria and overhead watering can
hasten the transmission. Since the bacteria are carried
in and on soil, water and plant material, there are many
opportunities for infection.
Prevention and control options
Preventing and controlling bacterial leaf spots and
wilts involves removing and destroying the infected
plant parts as soon as you notice the infection. Remove
infected tissues only when the plants are dry and be
sure to disinfect your tools (in 70 percent alcohol) and
hands (wash them in soap and water) between cuttings.
Buy only healthy plants and use sterile potting mix and
clean containers.
Prevention and control options
Virus diseases are difficult to manage once they are
established in the plant collection. The most effective
method for the control of viruses is to avoid purchasing
infected plant material and purchase resistant varieties when adding to your plant collection. You should
monitor the insect populations in your plant collection
since certain types of insects can vector viruses. Infected plants should be removed from the collection and
destroyed.
Pseudomonas (bacterial leaf spot) on chrysanthemums
Photo by Howard F. Schwartz, Colorado State University,
Bugwood.org
17
Pesticide misuse can contribute to several disease-like
symptoms, some of which are more serious than the
pest they were intended to eliminate. Physical damage
resulting from a dog, cat or other pet grazing in your
collection, accidentally overturning or dropping a plant,
or some other tissue damaging mishap can lead to unsightly or unhealthy plants.
Noninfectious abiotic plant
disorders
The interior plantscape can be a changing and unpredictable environment. The light, moisture, temperature
and air quality of the indoor environment often differ
from the plant’s natural habitat. Consequently, the interior plant is faced with an assortment of different yet
interrelated factors which affect its growth and therefore
its appearance.
Most noninfectious, abiotic plant disorders resemble
disease symptoms, though some are easily distinguished merely by attempting to correct the problem
and observing the results. The chart below lists the most
common symptoms and causal factors of several common abiotic plant disorders.
Nutrient availability is important for plants that are
confined in their growing habitats. Most interior plants
suffer from a lack of, or overabundance of, fertilizer,
which, in turn, affects their growth.
x
x
x
idity
hum
d
x
x
New leaves too small
x
x
x
Little or no new growth
x
x
x
Bud or flower drop
x
x
x
x
x
Leaf drop
x
x
x
x
x
x
x
x
x
x
x
x
x
Loss of varigation
x
x
x
x
Low
Root
boun
Gas
fume
s
draft
s
h
r cold
o hig
re to
Hot o
s
o low
eratu
Temp
re to
eratu
leave
Temp
r on
wate
Cold
Over
wate
ring
ring
rwate
Unde
soil s
alts
n
zatio
High
on
Over
fertili
lizati
rferti
crea
Unde
en in
t
Sudd
s ligh
x
x
x
x
x
Lower leaves turn yellow
Top or entire plant yellow
Symptoms
Exes
Insuf
ficien
t ligh
t
se in
light
Causal Factor
x
x
x
x
x
x
x
x
x
Brown or black leaf spots
x
x
x
Leaves curl or cup
x
x
x
x
Brown leaf margins or tips
x
x
x
x
x
x
x
x
Wilting
x
x
x
x
x
White or yellow leaf spots
Spindly growth
x
x
x
Root loss or rot
x
x
x
Leaf or petiole rot
x
x
Bladening of new growth
x
White crust on soil surface
x
Total plant collapse
18
x
x
x
x
x
x
biological controls and chemical controls directly affect the pest and its activities. Consider direct control
methods only when you’ve determined that the pest
is intolerable and harmful to you and your plants. You
should educate yourself about the many options of
direct control and choose the one (or combination of
methods) that most efficiently and safely reduces the
pest population.
Integrated Pest Management
Choosing a prevention or control option to
suit your needs and the situation
Integrated pest management is an approach to controlling pests by evaluating all the available control options
and choosing one or more in combination to achieve the
desired level of pest control having the least amount of
ecological and economic harm to the environment and
its inhabitants. Often an IPM strategy involves what is
simply a perceived pest, rather than an actual pest, and
learning how to tolerate a visitor or two is your “control option.” IPM strategies also incorporate chemical,
biological and physical controls for more direct pest
management practices, but these are put into action only
after the entire situation is evaluated. In all cases of pest
management, an integrated approach is best to ensure
that you are using the least harmful, most sensible and
most effective method to control your pest problem.
When considering pest control in the interior
plantscape, you need to look at the whole picture.
Examine your cultural practices, your choice of soil
and fertilizer, how much you water and how often, and
the overall environment in which the plant is living.
When you’ve decided that something needs to be done
to combat a pest, be sure you consider all your options prior to implementing a strategy. Having begun
a control strategy, follow up and monitor its success
or failure within your collection. If your strategy fails,
consider what may or may not have been successful
in the plan and redesign it so that previous faults are
corrected. When all else fails, remove the plant and its
pests from the collection and consider a new plant of a
different variety.
The interior plantscape is an ideal situation for IPM
activities; you have the opportunity to evaluate specific
plant needs and tolerance levels and can make educated
evaluations on the severity (or lack of) the pest problem. There are several things to consider when you are
evaluating a possible pest problem in your plant collection and they all revolve around the identity of the
pest, or the cause of the perceived problem. Perhaps
the insect you observe crawling on the plant is not a
plant feeder at all, but rather a beneficial predator that
is feeding on a small population of some other insect or
mite on the plant. Or perhaps the brown leaf tips you’ve
noticed are not from lack of water, but are actually a
result of a misapplication of a pesticide. Evaluating the
situation before you choose a solution is very important
for successful pest management.
About Pesticides
Any substance used to kill pests is called a pesticide.
Fungicides, insecticides and miticides are all types
of pesticides created to kill a specific group of pests.
There are several different kinds of pesticides, the most
well-known being the synthetically produced chemicals. Some naturally occurring substances derived from
plant sources are also registered as pesticides, as are
certain substances originating from mineral sources.
The microbial pesticides are those which are taken from
naturally occurring sources that cause disease in specific pests. Should you choose to use a pesticide in your
management strategy, you will need to consider several
important things.
Once you’ve identified the pest, you need to decide
at what level you can tolerate its presence in the plant
collection. Total elimination may not be possible unless you simply throw out the plant. Some degree of
tolerance is important, both for you and the plant. By
examining your plants and monitoring the pest’s activities you can acquire a good sense of how serious the
problem actually is, and begin to consider the different
means of control available and applicable. Often the
control measures are very simple, requiring nothing
more than a change in watering habits or relocating the
plant to a more favorable setting.
The Pesticide Label
More serious pest problems need greater attention and
direct suppression. Physical and mechanical controls,
19
All pesticides have labeling that is unique to the individual product. The label lists the uses for the pesticide
that are approved by the Environmental Protection
Agency (EPA), and if the intended use is not on the
label, then the product cannot be used in that manner.
The label is actually the law, and any use not listed on
the label is strictly prohibited. The label includes everything you need to know about the legal and safe use of
that particular product, such as its ingredients, application rates, hazards and more. Consultants or salespersons recommending a use for which a pesticide is NOT
labeled are in fact breaking the law.
the active ingredients that are contained in the product.
Those ingredients that are inert do not need to be identified, but do need to be listed by their percent of the total
contents.
The labeling on a pesticide is inclusive of the label on
the product container, any supplemental information
such as leaflets or attachments and information that is
referenced on the label. It is the applicator’s responsibility to comply with all of the label instructions.
ROUTE OF ENTRY STATEMENTS indicate which
area of your body (route of entry) you must particularly
protect, such as your mouth, skin and/or lungs. These
statements immediately follow the signal word on the
label or direct you to read elsewhere on the label.
The pesticide label usually has three different kinds
of names listed: the brand, trade or product name; the
chemical name; and the common name. The brand,
trade or product name is the name given to the pesticide by the manufacturer, and different manufacturers
may have a different brand name for the same pesticide
active ingredient. Do not choose a pesticide product by
brand name alone. The chemical name is the complex
name given to the chemicals and chemical structure that
make up the pesticide. The common name is a shorter
version of the complex chemical name.
The pesticide label has a STATEMENT OF PRACTICAL TREATMENT or FIRST AID STATEMENT that
tells you what to do in case of poisoning. All DANGER
labels and some WARNING and CAUTION labels
have a section on first aid, poison signs or symptoms,
note to physicians, an antidote and emergency assistance telephone number.
PROTECTIVE CLOTHING and EQUIPMENT
STATEMENTS tell you the clothing or equipment
required for specific tasks such as application, mixing
and loading. New enforceable product-specific labeling
statements will start appearing on agricultural, nursery
and greenhouse pesticide products sold after April 21,
1993. In most cases, the new label statements will list
the minimum clothing and equipment requirements as
well as posting and notification requirements. Also,
on April 15, 1994, generic label requirements such as
training and decontamination duties, etc., referenced
on the new product labels will become enforceable. A
user-friendly “How to Comply Guide” will be available
from pesticide dealers and from Cooperative Extension
Service offices explaining the generic label requirements.
Each label has a signal word that is used to indicate the
relative acute toxicity of the pesticide to humans. The
signal word lets you know how dangerous the pesticide
is and provides clues to your choice of safety precautions for both yourself and others around you. The
signal word DANGER, or WARNING, or CAUTION
appears on the front panel of the label.
DANGER classification is given to any product that is
highly toxic orally, dermally or through inhalation, or
causes severe eye or skin burning. All pesticides that
are highly toxic orally, dermally or through inhalation
will also carry the word POISON and a skull and crossbones symbol. A teaspoon or less taken orally could kill
an average-sized adult.
A pesticide may carry a RESTRICTED USE PESTICIDE STATEMENT, which means that the EPA has
classified that particular pesticide for restricted use
only. Any pesticide classified as “restricted” must carry
the following statement: “RESTRICTED USE PESTICIDE. For retail sale and use only by certified
applicators or persons under their direct supervision
and only for those uses covered by the certified applicator’s certification.”
WARNING indicates that the product is moderately
toxic orally, dermally or through inhalation, or causes
moderate eye and skin irritation. Ingesting as little as a
teaspoonful to as much as a tablespoonful could kill an
average-sized adult.
CAUTION is applied to any product which is slightly
toxic to relatively nontoxic orally, dermally, or through
inhalation, or that causes slight eye and/or skin irritation. As little as an ounce to more than a pint taken by
mouth could kill an average-sized adult.
Most pesticide labels have GENERAL ENVIRONMENTAL STATEMENTS that will remind you of the
potential harm to the environment that can result from
improper or careless use of the pesticide. Some pesticides are classified “RESTRICTED USE” because of
their potential hazard to the environment alone.
The pesticide label has several other important statements that further direct you to the proper and safe use
of the pesticide. The INGREDIENT STATEMENT lists
the official chemical names and/or common names for
If a particular pesticide is especially hazardous to wildlife or other organisms, the label will carry SPECIAL
20
Soluble or wettable powders are finely ground formulations that look like dusts. Most often they are mixed
with water before application. They are less likely than
liquid concentrates to cause plant damage since they
don’t contain any petroleum products. Powders are
not as easily absorbed through the skin and eye as are
liquid formulations. Disadvantages include the hazard
of inhalation and the need for constant agitation to keep
the powder in suspension. These types of treatments are
also difficult to mix in very hard or alkaline water and
may also leave a visible residue on the treated plant.
TOXICITY STATEMENTS that alert you to the special
precautions you need to take when using that particular
pesticide. If the pesticide is likely to harm plants, the
label will also warn you of its phytotoxic potential.
Pesticide labels carry a REENTRY STATEMENT that
tells you how long you must wait before you and others
can re-enter the treated area without wearing the appropriate protective clothing and equipment.
All pesticide labels contain various additional PRECAUTIONARY STATEMENTS that assist you in taking the proper precautions to protect anyone (including
domestic animals) who may be exposed.
Granular products are most often designed to be applied to the soil surface or incorporated into the soil.
Granules are ready to use, require no mixing and do not
pose as great a hazard from inhalation as do dusts and
powders. This type of formulation is designed to control
weeds, nematodes and insects living in the soil.
All pesticide labels provide you with general information on storage and disposal of the pesticide and its
container. You should try to determine the best storage
and disposal methods for your situation and location by
contacting the proper authorities.
An adjuvant is a chemical that is added to a pesticide
to increase its safety or effectiveness. These chemicals
may already be present in a ready-to-use formulation,
or you may be directed by the product label to add one
when mixing. Some examples of adjuvants are spreaders, which help the pesticide form a uniform layer over
the leaf surface, and stickers, which help the pesticide
adhere better to the surface being treated.
The illustration on page 23 shows a hypothetical
pesticide product label and identifies each of the label
statements mentioned above.
Pesticide Formulations
Products used for the control of pests on interior or
house plants are often marketed for convenience and
sold in a spray bottle, premixed and ready to use.
Ready-to-use products are convenient, and mixing errors are virtually nonexistent.
Pesticides are often described by the way in which they
act upon the disease or insect that is being treated. Contact pesticides are commonly applied to the leaves and
stems of plants, covering the insects or fungi present
on them. As the name implies, the fungus or insect is
killed upon contact. A soil drench may also be used as
a contact pesticide. In this type of treatment the soil is
saturated with a dilute solution of the desired chemical.
Because the insect or fungus is killed by coming into
contact with the pesticide, no feeding is necessary.
Emulsifiable concentrates usually contain an active
ingredient, one or more petroleum-based solvents and an
emulsifier that allow for easy mixing and little agitation.
These products are relatively easy to handle and store,
but due to their highly concentrated nature, a small error
in dilution may cause a large problem. Concentrates are
also easily absorbed through the skin and are generally
flammable and may be corrosive. Due to the petroleumbased nature of these products, plant damage (phytotoxicity) may result more often than with other formulations.
Systemic fungicides or insecticides are absorbed
through the leaves or roots of a plant and moved
through the plant’s vascular system providing protection to all parts of the plant. Systemics provide for
relatively long lasting control, killing pests that arrive
and feed on the plant after the application of the chemical. Systemics may be applied in a number of different
ways. They can be sprayed onto the foliage, applied as
granules and watered into the soil over a period of time,
or mixed with water and used as a soil drench, depending on the label instructions.
Dusts are ready-to-use and contain a low percentage of
active ingredient plus a very fine, dry inert carrier such
as clay or chalk. In situations where it is undesirable to
apply water to the foliage, dusts may provide the right
alternative. Because dusts are always used in their dry
form, drift into nontarget areas and the possibility of
inhalation can be disadvantageous. Dusts do not stick to
the plants as well as some other formulations.
21
References
Five Steps to Safe Use of Pesticides
All pesticides have labels that include their contents and
the type of plant or pest that the product may be used on.
Please review these five steps before making any pesticide application. Remember: THE LABEL IS THE
LAW.
Powell, Charles C. and R.K. Lindquist. 1986. Insect,
Mite and Disease Control in Commercial Floral and
Foliage Crops. Ohio State University Cooperative
Extension Service.
1. READ THE LABEL BEFORE BUYING. Make
sure that the product is labeled for the plant you
intend to use it on as well as the pest you wish to
control. Check the label for site suitability. If the
label does not specifically state that it is intended for
interior use, the product cannot legally or safely be
used for that purpose.
Ramsey, Carol A. and G.L. Thomasson, editors. 1989.
Private Applicator Pesticide Education Manual: A
Guide to Safe Use and Handling. Washington State
University Cooperative Extension Service.
Steiner, Marilyn Y. and Don P. Elliot. 1987. Biological
Pest Management for Interior Plantscapes, 2nd edition. Vegreville, AB: Alberta Environmental Centre.
2. READ THE LABEL BEFORE MIXING. Use the
rate indicated for the particular plant species you wish
to treat. It is illegal to use more than the recommended rate. Using more than the recommended rate may
also pose a health hazard for humans or pets and can
also result in plant injury or death. It is legal to use
less than the recommended rate, but keep in mind that
the treatment may prove ineffective. Follow any special instructions for the use of surfactants or spreaders. When indicated, wear protective clothing, glasses
and gloves when mixing or applying pesticides.
Albrecht, Mary L. and Dennis K. Kuhlman. 1991. Interior Landscape Pest Control. Kansas State University
Cooperative Extension Service.
Antonelli, A.L. and S.I. Collman. 1989. Houseplant
Pests. Washington State University Cooperative Extension Service.
Horst, Kenneth R. 1979. Westcott’s Plant Disease
Handbook, 4th edition. New York: Van Nostrand
Reinhold Publishing.
3. READ THE LABEL BEFORE APPLYING.
Check for any instructions that may refer to the conditions which must be met before making an application. Some examples of special instructions are: “Do
not apply if the temperature is above 90°F,” or “Do
not apply if the plant is wilted or severely stressed.”
Chase, A.R. 1987. Compendium of Ornamental Foliage
Plant Diseases. St. Paul, MN: The American Phytopathological Society.
Lucas, G.B., C.L. Campbell and L.T. Lucas. 1985.
Introduction to Plant Diseases: Identification and
Management. AVI Publishing Company, Inc.
4. READ THE LABEL BEFORE STORING. Always
store pesticides and other chemicals in their original
containers. Never store chemicals in any food or
beverage containers. Follow any recommendations
regarding storage sites or conditions. Directions of
this nature may be as follows: “Store away from heat
or flame.”
5. READ THE LABEL BEFORE DISPOSING. Unused pesticides or empty containers must be disposed of according to the label instructions. According to the EPA, empty and partially filled household
pesticide containers may be wrapped in paper and
discarded for curbside pickup. However, many
municipalities have rules and regulations prohibiting this disposal method of some household items.
Many communities conduct cleanup programs and
encourage citizens to turn in unwanted pesticides
during an annual cleanup day or week. Other communities may have a hazardous waste drop off site
which is open year-round.
Pirone, P.P. 1978. Diseases and Pests of Ornamental
Plants, 5th edition. John Wiley and Sons, Inc.
Nelson, P.V. 1985. Greenhouse Operation and Management, 3rd edition. Reston Publishing Company, Inc.
Pacific Northwest Plant Disease Control Handbook.
1991. University of Idaho Cooperative Extension Service, Oregon State University and Washington State
University.
22
Sample Label
Bug-Off
2 Insecticidal Soap
1
3 Concentrate
ACTIVE INGREDIENT....................................................By Wt.
Potassium Salts of Fatty Acids (Insecticidal soap):......49.0%
INERT INGREDIENTS:......................................................51%
TOTAL..........................................................................100.0%
4&5
NET CONTENTS 32 FL. OZ.
DIRECTIONS FOR USE
6
7
It is a violation of federal law to use this product in a manner inconsistent with its label.
Always use freshly mixed solution. Use soft water whenever possible. Do not use on new transplants or newly rooted cuttings. Do not apply
to plants in full sun. For control of ADELGIDS, APHIDS, EARWIGS, MEALYBUGS, CRICKETS, GRASSHOPPERS, LACEBUGS, TENT CATERPILLARS, PLANT BUGS, PSYLLIDS, SCALES, SPIDER MITES, THRIPS and WHITEFLIES on ornamental plants and vegetables grown in
and around the home. Mix 2.5 fluid ounces (5 tablespoons) per gallon of water. Apply whenever insects appear, being sure to thoroughly wet
both surfaces of infested leaves and branches. For aphids and mealybugs, spray again after 2 to 3 days. For other pests, spray weekly for 2
to 3 weeks or as needed. INDOOR PLANTS: Use as directed above. Be sure that spray penetrates dense foliage to wet all infested surfaces.
Do not use on crown of thorns; test spray other euphorbias, jade plants, palms and delicate ferns before making full application. For ROOT
MEALYBUGS on African violets, drench with tepid solution of 1 tablespoon per quart of water. VEGETABLES: Use as directed above on TOMATOES, PEPPERS and EGGPLANT to control aphids, spider mites and whiteflies up to day of harvest; on COLE CROPS to control aphids
and leaf hoppers up to day of harvest; on CUCUMBERS, SQUASH and MELONS to control aphids, spider mites, squash bugs and whiteflies
up to day of harvest; and on BEANS and PEAS to control aphids, leafhoppers, grasshoppers and spider mites up to day of harvest.
PRECAUTIONARY STATEMENTS 8
Hazards to humans and domestic animals
CAUTION: Harmful if swallowed. Avoid contamination of feed and food stuff. Avoid eye contact.
9 & 10
First aid (statement of practical treatment): In case of eye contact, flush with plenty of water. Get medical
attention if irritation persists.
11
12
Environmental hazards: Keep out of lakes, streams and ponds.
Physical or chemical hazards: Do not use or store near heat or open flame.
13
STORAGE AND DISPOSAL
Storage: Store in a cool place and keep container tightly sealed.
14
Disposal: For disposal of unused product, securely wrap original container in several layers of newspaper
and discard in trash. Do not reuse empty container. Rinse thoroughly before discarding in trash.
Distributed by
1.
2.
3.
4.
5.
6.
7.
8.
9.
16
BUG, INC.
123 Whitefly Lane
Cicley, AK 00011
EPA Reg. No. 946-23
17
EPA Est. No. 3344723-987-67
BRAND OR TRADE NAME
TYPE OF PESTICIDE
FORMULATION
ACTIVE INGREDIENT CHEMICAL NAME
ACTIVE INGREDIENT COMMON NAME
NET CONTENTS
DIRECTIONS FOR USE
PRECAUTIONARY STATEMENTS
SIGNAL WORD
10.
11.
12.
13.
14.
15.
16.
17.
18.
ROUTE OF ENTRY
FIRST AID
ENVIRONMENTAL HAZARDS
PHYSICAL OR CHEMICAL HAZARDS
STORAGE
DISPOSAL
NAME AND ADDRESS OF MANUFACTURER
EPA REGISTRATION NUMBER
EPA ESTABLISHMENT NUMBER
Sample Label
23
18
15
To simplify information, trade names of products have been used. No endorsement of named products by the University of Alaska Fairbanks Cooperative Extension Service is intended, nor is criticism implied of similar products that are not mentioned.
For more information, contact your local Cooperative Extension Service office or Michele Hébert, Extension Faculty,
Agriculture and Horticulture, at 907-474-2423 or [email protected]. This publication is based on Common Pests of
the Interior Plantscape, originally developed in 1993 by Wayne Vandre, Lois Bettini and Mary Comeau.
Reviewed by Michele Hébert in October 2010.
Visit the Cooperative Extension Service website at
www.uaf.edu/ces or call 1-877-520-5211
3-93/WV-LB-MC/500
Reprinted January 2011
America’s Arctic University
The University of Alaska Fairbanks Cooperative Extension Service programs are available to all, without regard to race, color, age, sex, creed, national
origin, or disability and in accordance with all applicable federal laws. Provided in furtherance of Cooperative Extension work, acts of May 8 and June 30,
1914, in cooperation with the U.S. Department of Agriculture, Fred Schlutt, Director of Cooperative Extension Service, University of Alaska Fairbanks.
The University of Alaska Fairbanks is an affirmative action/equal opportunity employer and educational institution.
©2011 University of Alaska Fairbanks. This publication may be photocopied or reprinted in its entirety for noncommercial purposes.