Plant Diseases

1. Plant Diseases

2. 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.

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, etc.

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

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11. 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

12. 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

13. 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

14. 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

15. 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

16. 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

17. 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

18. Important Plant Diseases-TurfMelting-Out • Control • Reduce shade • Mow at recommended heights • Improve soil aeration

19. 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

20. 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

21. 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

22. Important Plant Diseases-TurfPink Snow Mold • Favorable conditions • High humidity and temperatures around 40 degrees • Control • Adequate, balanced fertilizer • Reduce shade • Aeration • Drainage

23. 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

24. 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

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

26. 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

27. 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

28. 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

29. 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

30. 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

31. 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

32. 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

33. 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

34. 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

35. 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

36. 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

37. 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)

38. 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

39. 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

40. 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

41. 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

42. 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)

43. 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

44. 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

45. Important Plant Diseases-Ornamentals Fungus Leaf Spot • Symptoms • Difficult to diagnose from anthracnose • Variable spot colors and shapes • Causes • Wide variety of fungi

46. 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

47. 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

48. Important Plant Diseases-OrnamentalsOak Wilt • Causes • Fungus Ceratocytis fagacearum • Spread by • beetles from infected plants on their bodies f • Root grafts

49. 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

50. 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)