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Gardenia
Gardenia spp.
Propagation
Gardenia is usually propagated by softwood stem tip cuttings taken in early summer.
Root under intermittent mist for 4-8 weeks.
Pests and Diseases
The current Insect Management Guide for Commercial Foliage and Woody Ornamentals
can be found at http://edis.ifas.ufl.edu/IG012. The current Professional Disease
Management Guide for Ornamental Plants can be found at http://edis.ifas.ufl.edu/PP123.
Bacterial spot (Xanthomonas campestris)
Recognition: Bacterial spot can be identified by the
pinpoint-sized water-soaked spots on immature leaves or
unopened flower buds that turn black, often with a wide
yellow margin. The roughly circular or angular (stop
when they reach a leaf vein) spots enlarge and will cause
leaf drop.
Contributing factors: Cultivars vary in susceptibility.
Bacterial leaf spot is most severe in warm weather (7282 F).
Management recommendations: Remove infected plants and inspect new plants to keep
the disease out of your nursery. Minimize exposure to overhead irrigation and
rainfall which spread the disease.
Leaf spot (Myrothecium roridum)
Recognition: Leaf spots are watery and nearly always contain black and white fungal
fruiting bodies in concentric rings.
Contributing factors: Rare in landscape plantings. The spots
usually appear on wounded areas of leaves that have been broken
during handling. High humidity and temperatures of 77- 90 F, as
found in propagation houses, are ideal for disease development.
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Management recommendations: Avoid wounding leaves and keep foliage as dry as
possible, especially during propagation under mist. Proper cultural practices are
enough to control the disease under most circumstances. Several chemical
controls have been shown effective. See http://edis.ifas.ufl.edu/PP123 for current
recommendations.
Wet root rot diseases (Phytophthora and Pythium spp.)
Recognition: Above-ground symptoms are poor growth, thinning of the foliage, and
yellowing of leaves, with the oldest foliage affected first. These symptoms may be
one-sided on the plant. Wet rots cause a soft decay of the outer layers of roots,
which can be easily stripped off between two fingers, leaving the firm, white stele
intact as seen in the photo below.
Contributing factors: The disease is triggered by periods of excessive soil moisture.
Conditions that favor disease development include planting too deep, poor
drainage, shallow rooting, and poor water management.
Management recommendations: Check roots of nursery-grown plants before planting
into the landscape. Provide adequate drainage, and reduce irrigation. Apply
labeled fungicides if problem is diagnosed early and cultural problems corrected.
Stem canker (Phomopsis sp.)
Recognition: Cankers start as circular to oblong spots of darker brown than the normal
stem tissue. They develop into rough, cracked areas of cankerous growths near the
soil line or at the sites of wounds on cuttings. The foliage wilts above the
damaged stem or the whole plant may wilt and the flowers abscise before opening
if the main stem is affected.
Contributing factors: The fungal organism enters the plants through wounds. Prevent
damage to stems that would allow infection.
Management recommendations: Destroy any infected plants to prevent spread.
Fungicides against Phomopsis canker are only sometimes effective.
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Citrus whitefly
Recognition: The citrus whitefly, Dialeurodes citri (Ashmead), is about 1/8 inch in
length, and tends to hold its wings parallel to the leaf surface when at rest. The
nymphs are translucent, oval and very thin with no
waxy rods extending from the body as do some
whitefly species. The citrus whitefly lays yellow
eggs with a surface which is nearly smooth. They
suck the sap of the plant and exude honeydew,
which leads to sooty mold on the leaves and
possibly to increases in scale insects hiding under
the sooty mold.
Citrus whitefly
Contributing factors: More details about the
citrus whitefly can be found at
http://creatures.ifas.ufl.edu/citrus/citrus_whitefly.htm.
Management recommendations: There are several predators and parasites which attack
citrus whitefly, including a parasitic fungus. For severe infestations, chemicals
may be required. The latest chemical recommendations can be found at
http://edis.ifas.ufl.edu/IG012.
Citrus mealybug
Recognition: The Citrus mealybug is a soft-bodied insect with
piercing-sucking mouthparts, medium sized white waxy
filaments around the body, no long tail, and a single dark stripe
down the center of the body. This species produces an egg mass,
or ovisac, under the body of the female. They exude honeydew
which leads to black sooty mold growth.
Contributing factors: Mealybugs may attack year round, and
developmental time is decreased by high temperatures.
Management recommendations: Mealybugs are especially
difficult to control because of the waxy covering and the dense
colonies they form. There are several predators and parasites.
Cotton aphid
Recognition: The cotton aphid wingless adult, Aphis gossypii Glover, is 1/16 to 1/8 inch
long, yellow to dark green with a dusky
colored rear end. Winged adults are also
yellow to dark green but have a black head
and thorax. Their feeding causes leaves to
become chlorotic, distorted and curled and
die prematurely
Contributing factors: Primarily a spring
and summer pest, they may overwinter in
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greenhouses. In cold areas they overwinter as eggs that are yellow when first
deposited becoming shiny black. In warm areas, a generation can be completed
parthenogenetically in about seven days. They attack a wide range of plants,
including many melons and cotton, and may move from one field to another with
the wind. They transmit viruses.
Management recommendations: Natural enemies to be used include ladybird beetles,
syrphid flies and braconid wasps. If insecticides are used, be careful to thoroughly
cover foliage. Leaf distortions caused by their feeding will shelter them unless
system insecticides are used. Resistance to chlorinated hydrocarbon,
organophosphate and pyrethroid insecticides is widespread.
False spider mite
Recognition: False spider mites look similar to other
mites, but produce no webbing. Damage from these mites
ranges from faint brown flecks to large chlorotic areas on
the upper leaf surface, to brown areas on the lower leaf
surface, from their piercing-sucking mouth parts.
Contributing factors: False spider mites occur throughout
the year, but predominantly during the summer and fall
months.
Management recommendations: There are several predatory mites that can be used to
control false spider mites, as well as soaps and oils that will be less harmful to the
environment than chemicals. The latest chemical recommendations can be found
at http://edis.ifas.ufl.edu/IG012.
Scale (22 species, pyriform and green most common)
Recognition: Pyriform scale has a rather unique,
squashed pear appearance. The adult scales are about
1/10 of an inch both in length and also at their widest
point. Adults are a light greenish brown to tan or reddish
brown surrounded by a white cottony fringe. The
nymphs or immature scales are a translucent greenish
Pyriform scale
color.
The adult female green scale is shiny pale green with a
conspicuous black, irregular U-shaped internal marking
that is dorsally visible to the naked eye. Two submarginal black eye spots are also present and can be seen
with a hand lens. Adult scales are 2.5 to 3.25 mm. Dead
scales are light brown or buff color and the black internal
marking is lost. They are most often found on the
Adult female green scale
underside of the leaf.
Excreted honeydew attracts ants and causes sooty mold.
Ants will protect the scale from predation and reduce natural controls.
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Contributing factors: Damage can result in poor vigor and eventually defoliation as the
sap is sucked from the plants. There are several generations of this pest during the
year, so careful monitoring of plants is required to avoid scale population buildup.
Management recommendations: Chemical sprays should be directed to the underside of
the foliage and new growth. There are several entomogenous fungi (they grow on
the insect) that will naturally help to control green scale, but cannot be artificially
inoculated.
Thrips
Recognition: Thrips are relatively small, 0.5 to 5 mm long, insects with piercing-sucking
mouthparts. Thrips with an ovipositor usually lay
their eggs in plant tissue; those without an
ovipositor lay their eggs in crevices or under
bark. Thrips run, crawl, and jump and can move
rapidly. Flight is the major method of active
dispersal; however, they can be aerially
dispersed by drifting in wind currents for many
miles. If wings are present, they are long, narrow
and fringed with hairs. Both larvae and adults
feed on flowers, leaves, twigs, or buds, using
their piercing-sucking mouthparts, causing
structural abnormalities of foliage in the form of leaf malformation (distorted,
dwarfed, and matted), leaf fold, leaf roll, leaf blisters, and sometimes defoliation;
causing discoloration of petals, deformation, or scarring of flowers as well as
transmission of viruses.
Contributing factors: Thrips occur throughout the growing season. To aid in detecting
thrips, place a sheet of white paper beneath the leaves or flowers and shake the
plant. The thrips will fall onto the paper and can be more easily observed and
identified than when on the plant. Also look for the small spots of varnish-like
excrement on the leaves. If plants are flowering, be sure to inspect the flower
parts for thrips presence with a 10 to 15-power magnifying glass. Blue-colored
sticky traps have been developed for monitoring thrips and appear to be somewhat
more effective than yellow traps.
Management recommendations: There are several predatory mites, including
Neoseiulus mackanziei and Amblyseius cucumeris, which can be used for thrips
control. They also prey on spider mites if sufficient thrips are not present. Green
lacewing larvae, damsel bugs and pirate bugs are also predators of thrips as well
as many other pests of plants. Since thrips may come in large flights over an
extended period of time, insecticides which give good initial results but have a
short residual effect are generally inadequate for control of thrips infestations.
Systemics are highly effective and provide long-term control. Select insecticides
that have the least effect upon other non-target organisms.
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Root knot nematodes
Recognition: Poor growth, plant decline, yellowing leaves and thinning of the canopy may
be symptoms of nematode infestation.
Infected roots have obvious galls and
may be brown and stunted.
Contributing factors: The highest
populations of nematodes occur in
well-drained sandy soils where
previous crops have supported high
levels of nematodes.
Management recommendations:
Gardenias grafted on Gardenia
thunbergia rootstock resist root-knot
nematode attacks, but this rootstock
is too cold-sensitive for landscape
use in north Florida. Keep plants as
healthy as possible with adequate water and fertilizer to support new roots.
High organic matter levels in the soil will also discourage nematodes. No
chemical controls are available for use on existing plants. When replacing
plants, remove all roots and replace soil. Avoid replanting with susceptible
species, or fumigate before replanting.
Bud Drop
Recognition: Flower buds suddenly drop without any evidence of fungal infection,
although stem bases may turn brown or tan.
Contributing factors: Flower buds will often drop off gardenias that are subjected
to water, light or temperature stress.
Management recommendations: Maintain sufficient water when temperatures and
light are suddenly altered.
Sources:
1. Bradshaw, Joan. 2003. http://edis.ifas.ufl.edu/MG336. Gardenias. University of Florida
IFAS Extension.
2. Caldwell, Doug. University of Florida Collier County Extension Webpages.
http://collier.ifas.ufl.edu/Horticulture/pyriform%20scale.htm
3. Jones, Ronald K., and D. Michael Benson. 2001. Diseases of Woody Ornamentals and
Trees in Nurseries. APS Press. St. Paul Minnesota.
4. Lehman, Rayanne. Photo of false spider mite. Pennsylvania Department of
Agriculture. www.forestryimages.org
5. Osborne, Lance. http://www.mrec.ifas.ufl.edu/lso/
6. Short, Donald E., Gary W. Simone and Robert A. Dunn. 2001. CommercialOrnamental
Nursery Scouting Manual. University of Florida IFAS Extension SP 235.
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7. Disease photos courtesy of Florida Dept. of Agriculture and Consumer Services,
Division of Plant Industry.
8. University of Florida IFAS Extension Woodybug webpages at
http://woodypest.ifas.ufl.edu/.
9. University of Florida Featured Creatures Webpages.
http://creatures.ifas.ufl.edu/orn/scales/green_scale.htm
10. University of Florida Landscape Plant Propagation Information.
http://hort.ufl.edu/lppi/
Prepared by:
Juanita Popenoe, PhD, Extension Faculty, Regional Commercial Horticulture
Lake County Extension, 1951 Woodlea Rd., Tavares, FL 32778-4052
Tel.: (352) 343-4101, FAX: (352) 343-2767 January 2008
The Institute of Food and Agricultural Science (IFAS) is an Equal Opportunity Institution authorized to provide research, educational information and
other services only to individuals and institutions that function without regard to race, creed, color, religion, age, disability, sex, sexual orientation,
marital status, national origin, political opinions or affiliations. U.S. DEPARTMENT OF AGRICULTURE, COOPERATIVE EXTENSION SERVICE,
UNIVERSITY OF FLORIDA, IFAS, FLORIDA A. & M. UNIVERSITY COOPERATIVE EXTENSION PROGRAM, AND BOARDS OF COUNTY
COMMISSIONERS COOPERATING.
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