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Turf and Ornamental Plant Diseases Control Guide

Learn about abiotic and biotic plant diseases affecting turf and ornamental plants. Understand the causes, symptoms, and control measures for common diseases like Brown Patch, Dollar Spot, Leaf Spot, Melting-Out, Necrotic Ring Spot, and Pink Snow Mold.

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Turf and Ornamental Plant Diseases Control Guide

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  1. Plant Diseases Category E Turf and Ornamentals Pesticide Applicator Training Manual Chapter 5

  2. Terms • Abiotic plant disease—caused by unfavorable growing. • Biotic plant disease —caused by plant pathogens. Category E--- Chapter 12 Soil Fumigation

  3. Introduction • Plant disease—a 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

  6. 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

  7. 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

  8. 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

  9. 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

  10. 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

  12. 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

  13. 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

  14. 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

  15. 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

  16. 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

  17. 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

  19. 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

  24. Important Plant Diseases-TurfRust • Symptoms • Begins as light green or yellow flecks becomes • Reddish brown to orange (spores) • Causes • Puccinia species

  25. 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

  26. 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

  27. 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

  30. 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

  31. 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

  33. 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

  35. 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)

  37. 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

  39. 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 • BacteriumErwinia 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

  48. 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

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