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Plant Diseases Did not include Hawthorne leaf blight, mosaic, or Rhabdocline leaf cast
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Terms Abiotic plant disease—caused by unfavorable growing conditions.
Biotic plant disease —caused by plant pathogens. Pathogen- an infectious, biological agent such as a virus, bacteria or fungus that causes disease to its host.
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Introduction Plant disease—a harmful change in the growth of a plant.
Fumigants are broad spectrum biocides and kill most fungi, soil insects, nematodes, and weeds. Fumigants will not kill most of the soil resident bacterial diseases or viruses. Methyl bromide is the most important soil fumigant. It is used for high value crops such as tomatoes, peppers, strawberries, seed potatoes, and several ornamentals. Methyl bromide is also highly destructive to atmospheric ozone. Methyl bromide usage is being phased out under international treaty (1991 Montreal Protocol). Florida estimates 61-63% reduction in tomato and pepper production unless alternatives to methyl bromide can be found. Metam-sodium is the active ingredient in several products lines including Vapam®, Busan®, Nemasol®, and Metam® products.
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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
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Biotic Plant Diseases Plant disease triangle Causal agents: Fungi
Bacteria Viruses, etc.
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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)
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-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
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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
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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
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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
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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
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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
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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
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Important Plant Diseases-Turf Melting-Out
Control Reduce shade Mow at recommended heights Improve soil aeration
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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
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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
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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
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Important Plant Diseases-Turf Pink Snow Mold
Favorable conditions High humidity and temperatures around 40 degrees Control Adequate, balanced fertilizer Reduce shade Aeration Drainage
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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
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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-Turf Rust
Symptoms Begins as light green or yellow flecks becomes Reddish brown to orange (spores) Causes Puccinia species
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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
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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
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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
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Important Plant Diseases-Turf Stripe 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
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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-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
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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 Antagonistic strains Chemically kill grass in infested area Remove infected sod (and white mycelium), mix soils and mycelium rototill to 8 inches sod or reseed
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Important Plant Diseases-Turf Pythium Blight
Symptoms Large areas can die in 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-Turf Pythium Blight
Favorable conditions Temperatures 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
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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
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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
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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-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
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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-Ornamentals Cytospora 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
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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
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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)
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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
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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
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Important Plant Diseases-Ornamentals Fungus Leaf Spot
Symptoms Difficult to diagnose from anthracnose Variable spot colors and shapes Causes Wide variety of fungi
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Important Plant Diseases-Ornamentals Fungus 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
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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
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Important Plant Diseases-Ornamentals Oak Wilt
Causes Fungus Ceratocytis fagacearum Spread by beetles from infected plants on their bodies f Root grafts
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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
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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 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) The latex paint will mask the odor of the wound from beetles
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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 Pustules are small, blister like bumps caused by spores pushing their way from underneath the epidermis of the leaf
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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
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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
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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
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Important Plant Diseases-Ornamentals Sphaeropsis 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-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
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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
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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
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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
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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
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