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Plant Diseases
Category E Turf and Ornamentals
Pesticide Applicator Training Manual
Chapter 5
Terms
• Abiotic plant disease—caused by unfavorable
growing.
• Biotic plant disease —caused by plant pathogens.
Category E--- Chapter 12 Soil Fumigation
Introduction
• Plant disease—a harmful change in the growth of a
plant.
Abiotic Plant Diseases
• Not caused by pathogens
• Caused by unfavorable growing conditions
– Improper light
– Temperature extremes
– Mechanical injury
• Abiotic diseases lead to stress that can increase
susceptibility to damage from insects or
pathogenic diseases
• Most abiotic plant diseases are avoidable
Biotic Plant Diseases
• Plant disease triangle
• Causal agents:
– Fungi
– Bacteria
– Viruses
– Nematodes
Causal Agents (Pathogens)
• Fungi
– Most turf and ornamental disease are caused by
fungi
– Do not produce their own food
– Reproduce by forming spores
• Spread
– Some by water
– Some by wind
– Mechanical/animal
– Infected plants
Causal Agents (Pathogens)
• Bacteria
– Single celled microbes
– Enter plants through injuries or natural
openings
• Spread
– Some by water
– Some by wind
– Some in soil
– Mechanical/animal
– Infected plants
Causal Agents (Viruses)
• Viruses
– Smaller than cells---multiply in cells
– Often spread
– Infected plants must be removed---no cures
• Spread
– Mechanical---e.g. contaminated equipment
– Contact between plants
– Sucking insects
Susceptible Host Plants
• Ornamental plants vary in disease resistance
• Susceptibility increases with stress
• Symptoms of decline
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Late flowering or leaf emergence
Smaller leaf size
Less shoot growth
Excessive water spouts
Important Plant Diseases-Turf
Brown Patch
• Symptoms
– Irregular brown areas inches to feet wide
– Grass leaves turn olive green then wilt, turn
light brown, and die.
– Stems and crowns can also be infected
• Causes
– All grasses susceptible
– Caused by Rhizoctonia solani, reside in soil
Important Plant Diseases-Turf
Brown Patch
• Favorable conditions
– Excess thatch
– High temperatures (75-90 degrees)
• Control
• Aerate
• Water to 4-6 inches depth when needed
• Avoid excess nitrogen
Important Plant Diseases-Turf
Dollar Spot
• Symptoms
– Small, bleached out or straw-colored spots
– Seldom larger than 2 inches in close-mowed
turf
– On taller grass (1-3 inches) spots can be 3-6
inches in diameter
– Spots can merge together
– Does not kill the grass plants
• Causes
– Caused by fungi
– indicates Nitrogen deficiency
Important Plant Diseases-Turf
Leaf Spot
• Favorable conditions
– Nitrogen deficiency
– Warm days with cool nights
– High humidity
• Control
– Adequate nitrogen and potassium
– Water in the morning let turf dry out before
dusk
– Preventative fungicides
– Curative fungicides
Important Plant Diseases-Turf
Leaf Spot
• Symptoms
– Start as small, dark purple or black spots
– Become oval spots with buff centers and purple
margins
• Causes
– Primary cause--- fungus Bipolaris
sorokinianum
Important Plant Diseases-Turf
Leaf Spot
• Favorable conditions
– Dry periods alternating with cloudy, wet
weather
• Control
– Avoid over-lush turf
– Mow so that no more than 1/3 of the leaf blades
are cut
– Resistant cultivars
Important Plant Diseases-Turf
Melting-Out
• Symptoms
– Circular to elongated, purplish or brownish
spots
– General e.g. spread throughout the grass
• Causes
– Melting-out is the summer phase of leaf spot
– Brent grass, fescues, ryegrass and
burmudagrass---fungus Bipolaris sorokinianum
Important Plant Diseases-Turf
Melting-Out
• Control
– Reduce shade
– Mow at recommended heights
– Improve soil aeration
Important Plant Diseases-Turf
Necrotic Ring Spot
• Symptoms
– Begins as scattered light green patches 2-6
inches in diameter
– Patches enlarge and fade to tan, may become
sunken . Streaks or crescents 1-3 or more feet
in diameter
– Patches can increase over the years
• Causes
– Fungus Leptosphaeria korrae
– Formerly called fusarium blight
Important Plant Diseases-Turf
Necrotic Ring Spot
• Favorable conditions
– Cool or mild periods followed by dry, hot
conditions
– Widespread disease of Kentucky and annual
bluegrass that is intensively managed---follows
stress
• Control
– Good cultural practices: aeration, drainage,
balance of fertilizers, water in the morning
– Resistant cultivars
– Systemic fungicides
Important Plant Diseases-Turf
Pink Snow Mold
• Symptoms
– Appears first as snow melts
– Round, water-soaked spots 1-3 inches in
diameter
• Causes
– Fungi Fusarium nivale or Microdochium nivale
– These fungi inactive in warm dry conditions
Important Plant Diseases-Turf
Pink Snow Mold
• Favorable conditions
– High humidity and temperatures around 40
degrees
• Control
– Adequate, balanced fertilizer
– Reduce shade
– Aeration
– Drainage
Important Plant Diseases-Turf
Powdery Mildew on Turf
• Symptoms
– Thin, white powdery coating
– Lives primarily on outer surfaces
• Causes
– Fungi Fusarium nivale or Microdochium nivale
– These fungi inactive in warm dry conditions
Important Plant Diseases-Turf
Powdery Mildew on Turf
• Favorable conditions
– Cool (55-70 degrees) cloudy weather
– Important disease on Kentucky bluegrasses
during extended periods of low light, especially
in areas with poor air circulation
• Control
– Include shade tolerant cultivars in seed
mixtures
– Prune trees and shrubs to permit light to reach
turf
– Deep, infrequent watering
Important Plant Diseases-Turf
Rust
• Symptoms
– Begins as light green or yellow flecks becomes
– Reddish brown to orange (spores)
• Causes
– Puccinia species
Important Plant Diseases-Turf
Rust
• Favorable conditions
– Cool to warm, moist weather
– Dew or condensed moisture on plants for 12 hours
• Control
– Maintain healthy growth with fertilizer and
irrigation
– Remove infected portions of leaves with weekly
mowing
– Curative fungicides
Important Plant Diseases-Turf
Slime Molds
• Symptoms
– Slimy masses 1 inch to 2 feet in diameter
– Shades of grays and yellow
– Easily removable
• Causes
– Non parasitic on turf---feed on organic matter
Important Plant Diseases-Turf
Slime Molds
• Favorable conditions
– Warm, moist weather and high humidity
– Spread by winds, water, equipment
• Control
– Will disappear but can rake or hose-off
Important Plant Diseases-Turf
Stripe Smut
• Symptoms
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Long, black stripes (pustules)
Grass leaves curl, become shredded and die
From a distance appears clumpy and patchy
Plants die when hot weather occurs
• Causes
– Fungus Ustilago striformis often contaminates turf
seed
– Can remain dormant for 3 years in soil
Important Plant Diseases-Turf
Stripe Smut
• Favorable conditions
– Moderate temperatures (50-65 degrees)
– Prevalent in spring and fall
– Occurs on other grasses but more common on
bluegrasses
• Control
– Resistant cultivars of bluegrass
– Seed treatment with fungicides
– Dystemic curative fungicides
Important Plant Diseases-Turf
Fairy Ring
• Symptoms
– Circular or semi-circular dark green band on turf
(released nitrogen from breakdown of organic matter in
soil)
– Mushrooms will often develop around edge after wet
weather
• Causes
– Several fungi
– Occurs in areas with high levels of organic
material e.g. thatch
Important Plant Diseases-Turf
Fairy Ring
• Favorable conditions
– Presence of high concentrations of organic matter
e.g. tree stumps, roots, construction lumber
• Control
– Remove excess organic matter
– Antagonist strains for heavy infestations
Important Plant Diseases-Turf
Pythium Blight
• Symptoms
– Large areas can die in 24-48 hours when
conditions favoring pythium blight occur
– Round to irregular, dark and water-soaked,
greasy or slimy
– Sunken patches 6-12 inches wide
– Reddish brown areas fade to tan and die
• Causes
– Several species of Pythium fungi
Important Plant Diseases-Turf
Pythium Blight
• Favorable conditions
– Temperatures 80-90 degrees with 90% RH (relative
humidity) and warm nights (.70 degrees) for most
Pythium but some thrive in cool weather
– Waterlogged soils with heavy thatch
– Excess nitrogen
• Control
– Improve drainage
– Systemic fungicide prior to hot, humid weather
Important Plant Diseases-Turf
Summer Patch
• Symptoms
– Bluish-green patches become wilted then die
– Patches become circular or crescent-shaped.
• Causes
– Several species of Pythium fungi
Important Plant Diseases-Turf
Summer Patch
• Favorable conditions
– Usually occurs when a wet period follows hot,
dry weather
– Frequent or excessive watering
• Control
– Before planting new turf remove stumps and
construction material
– Avoid mowing or walking on wet turf
– Apply systemic fungicides when temperatures
reach 70 degrees
Important Plant Diseases-Ornamentals
Anthracnose
• Symptoms
– Leaf buds do not emerge in spring
– Defoliation from progressive death of mature leaf
tissue along leaf midrib or veins
• Causes
– Anthracnose in many common tree species
– Transitional disease, intermediate between a leaf
and stem disease caused by fungi (genus
Gnomonia)
Important Plant Diseases-Ornamentals
Anthracnose
• Favorable conditions
– Disease begins in late winter or early spring during
periods of warm weather
– Splashing of spores during warm. Wet weather spreads
the disease
• Control
– Fungicide application on leaves and buds during
emergence
– Cultural practices including avoiding planting species
that are especially susceptible, maintaining adequate
irrigation and fertilization
Important Plant Diseases-Ornamentals
Cytospora Canker
• Symptoms
– Affects poplar and willow
– Circular or irregular cankers first appear as
brown, sunken areas on younger trees
– Cankers often start at wound openings
• Causes
– Fungus Cytospora chrysosperma
Important Plant Diseases-Ornamentals
Cytospora Canker
• Favorable conditions
– Fungus is opportunistic, infects weakened or
wounded tissues
– Spread by splashing rain, wind
• Control
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Remove dead and dying branches
Clean pruning tools
Fertilize
Deep water (10-12 inches)
No fungicides are available
Important Plant Diseases-Ornamentals
Dutch Elm Disease
• Symptoms
– Leaves brown and curl---usually drop early
– Large elms may die over 2 or more years
• Causes
– Fungus Ceratocysitus ulmi
– Infects elms and closely related plants
– Transmitted by:
• Elm bark beetles
• Root grafts with adjacent trees
• Pruning tools
Important Plant Diseases-Ornamentals
Dutch Elm Disease
• Control
– Plant cultivars with superior resistance (Siberian and
Chinese)
– Water and fertilize
– Spray with appropriate insecticide in late winter/early
spring before the buds swell (requires special training
and equipment)
– Systemic injections
– Halt transmission through root grafts (see oak wilt
procedures)
Important Plant Diseases-Ornamentals
Fire Blight
• Symptoms
– Infected flowers first appear water-soaked
– Leaves and stems then appear brown or black as though
scorched by fire
• Causes/favorable conditions
– Bacterium Erwinia amylovora overwinters in plant
tissues and emerges when temps reach 65 degrees
– Spread by insects, wind, water, hail
Important Plant Diseases-Ornamentals
Fire Blight
• Control
– Plant resistant varieties of apple, crabapple, and pear
where available
– Good cultural practices (fertility, watering, drainage)
– Prune in dormant season and disinfect tools between
cuts with 70% rubbing alcohol solution
– 6 inches of mulch around susceptible tress reduces
chance of infection
Important Plant Diseases-Ornamentals
Fungus Leaf Spot
• Symptoms
– Difficult to diagnose from anthracnose
– Variable spot colors and shapes
• Causes
– Wide variety of fungi
Important Plant Diseases-Ornamentals
Fungus Leaf Spot
• Favorable conditions
– Cool weather, light rains, high humidity
– Crowded plantings
• Control
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Preventive measures usually not needed
Good culture
Remove fallen leaves and branches
Proper spacing
Important Plant Diseases-Ornamentals
Juniper Twig Blight
• Symptoms
– In spring tips of twigs and branches turn light green
then brown
– Usually affects branches less than 1/3 inch diameter
– Spores emerge during wet weather in spring and early
summer
• Causes
– Fungus Phomopsis juniperova
• Controls
– Cultural practices
– Provide ventilation in shaded areas
– Fungicides every 2 weeks early spring to fall
Important Plant Diseases-Ornamentals
Oak Wilt
• Causes
– Fungus Ceratocytis fagacearum
– Spread by
• beetles from infected plants on their bodies f
• Root grafts
Important Plant Diseases-Ornamentals
Oak Wilt
• Symptoms
– Impairs water conduction from roots to
branches and leaves
– Trees wilt from the top down and leaves wilt
from the tips to the base
– Fallen leaves have brown tips and green along
the main vein
Important Plant Diseases-Ornamentals
Oak Wilt
• Favorable conditions
• Control
– Avoid pruning wounding) from April 15 to July 1st if
wound occurs during that time cover with tree wound
dressing or latex paint---this is the critical period of
beetle movement
– Isolate infected trees---preventing root grafts--trenching machine or vibratory plow (cut to 4.5-5.0 feet
deep)
– Red and black oaks most susceptible
– Reduce spore quantity---cover pruned wood, debark
branches that are 3 inches and over (fungus mats
below bark)
Important Plant Diseases-Ornamentals
Rust
• Symptoms
– Bright orange, yellow, chocolate brown or
black pustules
• Causes
– Several fungi
• Control
– Alternate hosts e.g. junipers and cedars one year,--apple, crabapple, hawthorne, mountain ash the next
– Disease free plants
– Prune infested tissue
Important Plant Diseases-Ornamentals
Scab
• Symptoms
– Apple scab develops as circular lesions during
leaf expansion in spring. Color progresses from
dark green to black
– Fruit can be infected at any time during
development
• Cause
– Fungus Fusicladium saliciperdum
Important Plant Diseases-Ornamentals
Scab
• Favorable conditions
– Apple scab overwinters on leaf litter
– Wet weather during bud break spreads spores
– Cool, wet conditions
• Control
– Plant resistant varieties when available
– Prune out diseased tissue
– 3-4 applications of fungicides at 10 day intervals
starting just before bud break
Important Plant Diseases-Ornamentals
Sphaeropsis Blight (Diplodia Tip Blight)
• Symptoms
– On new, emerging needles browning occurs near the
base of the needle and progress to the tip. Ooze forms
– Infection spread to twigs and die back to the next whorl
– Begins with lower branches and progresses up the tree
over successive years
– In severe cases the tree dies
• Causes
– Fungus Sphaeropsis sainea
Important Plant Diseases-Ornamentals
Sphaeropsis Blight (Diplodia Tip Blight)
• Control
– Removal of infected branches
– Balanced fertilizers in spring
– Adequate watering
Important Plant Diseases-Ornamentals
Phytopthora
• Symptoms
– Variable, may be slow decline or rapid death
during dry weather
– Root and crown root
– Symptoms may include chlorosis, sparse
foliage, reduced sized foliage in trees and
shrubs
• Causes
– Fungi from the genus Phytopthora soilborne
Important Plant Diseases-Ornamentals
Phytopthora
• Favorable conditions
– High occurrence in areas with high soil moisture
and low fertility
• Control
– Plant in well drained soil
– Allow plants to dry out between irrigation
– Systemic fungicides
Important Plant Diseases-Ornamentals
Verticillium
• Symptoms
– Especially common on maples but can occur on
several landscape trees and shrubs
– Usually the leaves on the entire plant or all the
leaves on one side of the plant suddenly wilt
– Dieback
– May progress through several years
• Causes
– Fungi from genus Verticillium
– Soilborne and spread by contamination
Important Plant Diseases-Ornamentals
Verticillium
• Control
– Plant disease-free nursery stock
– Avoid wounding and contaminated tools
– Avoid excess nitrogen
– Replace infected plant with resistant varieties or
immune species
Important Plant Diseases-Ornamentals
Powdery Mildew
• Symptoms
– White, powdery spots that grow to cover the entire
surface
– Young plants most vulnerable, especially in shade
– Dwarfing, distortion, yellowing.
– Leaves may drop
• Causes
– Over 1000 species of fungi primarily Microsphaera and
Odium
Important Plant Diseases-Ornamentals
Powdery Mildew
• Favorable conditions
– Shade
– Areas with poor air circulation
– Easily spread by splashing water
• Control
– Prune affect parts
– Select plants for resistance
– Because powdery mildew are usually external they can
be controlled ---curative fungicides