Plant Diseases

1
Plant Diseases

• Category E Turf and Ornamentals
• Pesticide Applicator Training Manual Chapter 5

2
Terms

• Abiotic plant diseasecaused by unfavorable
  growing.
• Biotic plant disease caused by plant pathogens.

Category E--- Chapter 12 Soil Fumigation
3
Introduction

• Plant diseasea harmful change in the growth of a
  plant.

4
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

5
Biotic Plant Diseases

• Plant disease triangle
• Causal agents
• Fungi
• Bacteria
• Viruses
• Nematodes

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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

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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

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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

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Susceptible Host Plants

• Ornamental plants vary in disease resistance
• Susceptibility increases with stress
• Symptoms of decline
• Late flowering or leaf emergence
• Smaller leaf size
• Less shoot growth
• Excessive water spouts

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Important Plant Diseases-TurfBrown 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

11
Important Plant Diseases-TurfBrown Patch

• Favorable conditions
• Excess thatch
• High temperatures (75-90 degrees)
• Control
• Aerate
• Water to 4-6 inches depth when needed
• Avoid excess nitrogen

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Important Plant Diseases-TurfDollar 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

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Important Plant Diseases-TurfLeaf 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

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Important Plant Diseases-TurfLeaf 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

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Important Plant Diseases-TurfLeaf 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

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Important Plant Diseases-TurfMelting-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

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Important Plant Diseases-TurfMelting-Out

• Control
• Reduce shade
• Mow at recommended heights
• Improve soil aeration

18
Important Plant Diseases-TurfNecrotic 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

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Important Plant Diseases-TurfNecrotic 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

20
Important Plant Diseases-TurfPink 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

21
Important Plant Diseases-TurfPink Snow Mold

• Favorable conditions
• High humidity and temperatures around 40 degrees
• Control
• Adequate, balanced fertilizer
• Reduce shade
• Aeration
• Drainage

22
Important Plant Diseases-TurfPowdery 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

23
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

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Important Plant Diseases-TurfRust

• Symptoms
• Begins as light green or yellow flecks becomes
• Reddish brown to orange (spores)
• Causes
• Puccinia species

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Important Plant Diseases-TurfRust

• 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

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Important Plant Diseases-TurfSlime 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

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Important Plant Diseases-TurfSlime Molds

• Favorable conditions
• Warm, moist weather and high humidity
• Spread by winds, water, equipment
• Control
• Will disappear but can rake or hose-off

28
Important Plant Diseases-TurfStripe Smut

• Symptoms
• 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

29
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

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Important Plant Diseases-TurfFairy 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

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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

32
Important Plant Diseases-TurfPythium 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

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Important Plant Diseases-TurfPythium 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

34
Important Plant Diseases-TurfSummer Patch

• Symptoms
• Bluish-green patches become wilted then die
• Patches become circular or crescent-shaped.
• Causes
• Several species of Pythium fungi

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Important Plant Diseases-TurfSummer 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

36
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)
  

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Important Plant Diseases-OrnamentalsAnthracnose

• 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

38
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

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Important Plant Diseases-OrnamentalsCytospora
Canker

• Favorable conditions
• Fungus is opportunistic, infects weakened or
  wounded tissues
• Spread by splashing rain, wind
• Control
• Remove dead and dying branches
• Clean pruning tools
• Fertilize
• Deep water (10-12 inches)
• No fungicides are available

40
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

41
Important Plant Diseases-OrnamentalsDutch 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)

42
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

43
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

44
Important Plant Diseases-Ornamentals Fungus Leaf
Spot

• Symptoms
• Difficult to diagnose from anthracnose
• Variable spot colors and shapes
• Causes
• Wide variety of fungi

45
Important Plant Diseases-OrnamentalsFungus Leaf
Spot

• Favorable conditions
• Cool weather, light rains, high humidity
• Crowded plantings
• Control
• Preventive measures usually not needed
• Good culture
• Remove fallen leaves and branches
• Proper spacing

46
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

47
Important Plant Diseases-OrnamentalsOak Wilt

• Causes
• Fungus Ceratocytis fagacearum
• Spread by
• beetles from infected plants on their bodies f
• Root grafts

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Important Plant Diseases-OrnamentalsOak 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

49
Important Plant Diseases-OrnamentalsOak 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)

50
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

51
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

52
Important Plant Diseases-OrnamentalsScab

• 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

53
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

54
Important Plant Diseases-OrnamentalsSphaeropsis
Blight (Diplodia Tip Blight)

• Control
• Removal of infected branches
• Balanced fertilizers in spring
• Adequate watering

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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

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Important Plant Diseases-OrnamentalsPhytopthora

• 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

57
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

58
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

59
Important Plant Diseases-OrnamentalsPowdery
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

60
Important Plant Diseases-OrnamentalsPowdery
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