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DOLLAR SPOT

DOLLAR SPOT. caused by. Sclerotinia homoeocarpa. Knowledge Requirements. When you complete this section, you should be able to answer these questions. What are the best diagnostic signs and symptoms of dollar spot? Is the pathogen a spore-former or a non-spore-former?

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DOLLAR SPOT

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  1. DOLLAR SPOT caused by Sclerotinia homoeocarpa

  2. Knowledge Requirements When you complete this section, you should be able to answer these questions • What are the best diagnostic signs and symptoms of dollar spot? • Is the pathogen a spore-former or a non-spore-former? • How does the pathogen survive adverse conditions? • How does the pathogen infect turfgrass plants? • What species of turfgrass are susceptible? • What effects do nutrients such as N, P & K have on the disease? • What environmental conditions are required for DS to develop? • Name a contact and penetrant fungicide that will control dollar spot. • 9. Name some fungicides that are considered ‘high risk’ for selection of • of fungicide resistant biotypes of the dollar spot fungus. • 10. During what season(s) are preventive applications of dollar spot • fungicides applied in GA? • 11. What species of turfgrass are resistant or immune to dollar spot? • 12. What turf nutrients suppress dollar spot? • 13. In what ways can the environment be manipulated to suppress • dollar spot? • 14. What can be done to avoid the development of fungicide resistant DS?

  3. Sclerotinia homoeocarpa • Nonspore-forming fungus • Survives (overwinters) as dormant mycelium • in previously infected leaf tissue. • Hyphae emerge from tissue at 50-90°F • and infect new leaves during extended • periods (>10 hrs) of leaf wetness. • Hyphae enter leaves through hydathodes, • stomates, and the cut end of leaves.

  4. DOLLAR SPOT Susceptible grasses All common species of warm and cool season grasses. Some cultivars of warm and cool season grasses are less susceptible than others.

  5. DOLLAR SPOT Favorable Environment • Night temperatures > 50°F and day temps • <90°F. • -More than 10 hrs. of leaf wetness per day for • several days. • -Disease is severe on turf subjected to drought • stress and low fertility.

  6. Dollar spot is named for the ‘silver dollar’ size patches that develop on close cut turf such as this creeping bentgrass golf green.

  7. Individual dollar spots are often less distinct on turf that is mowed at heights >0.5 inch as on this bermudagrass lawn.

  8. Sometimes dollar spot doesn’t look like ‘dollar spot’ as on this zoysia grass. So how do we make a diagnosis?

  9. The best diagnostic feature of dollar spot is the formation of bleached white lesions that cut across leaf blades. Lesions are usually bordered by dark brown tissue.

  10. Dollar spot lesion on bluegrass. Lesion may collapse in the middle, producing an hour-glass shape.

  11. Infection often occurs at the leaf tip or margin. Lesions then extent down or across the leaf. Dollar spot lesion on bermudagrass Note bleached white color and dark border.

  12. Formation of white mycelium growing from infected leaves is a diagnostic ‘sign’ of dollar spot.

  13. Mycelium can often be observed in the morning when leaves are wet from dew, rain or irrigation.

  14. Mycelium and infected leaves can adhere to mowers and other equipment resulting in a directional spread of disease. Mowing direction

  15. Management of Dollar Spot

  16. Management of Dollar Spot Resistant Species and Cultivars Warm Season Grasses – Bermudagrass and Seashore Paspalum are more susceptible than other species of warm season grasses. Cool Season Grasses – Bentgrass and annual bluegrass are the most susceptible cool season grasses.

  17. Management of Dollar Spot Resistant Species and Cultivars Bermudagrass Information on cultivar differences in susceptibility to dollar spot is limited. Paspalum The cultivars Durban and SeaIsle 1 are less susceptible than some other cultivars.

  18. Management of Dollar Spot Resistant Species and Cultivars Bentgrasses • Colonial bentgrass is less susceptible than • creeping bentgrass.

  19. Management of Dollar Spot Resistant Species and Cultivars Bentgrasses • Colonial bents are less susceptible than • creeping bents. • - Among creeping bentgrass cultivars, the • the following have some resistance: L-93, • SR7200, Bavaria, Vesper, A-1 and A-2.

  20. Management of Dollar Spot Resistant Species and Cultivars Bentgrasses • Colonial bents are less susceptible than • creeping bents. • - Among creeping bentgrass cultivars, the • the following have some resistance: L-93, • SR7200, Bavaria, Vesper, A-1 and A-2. • - Highly susceptible creeping bents include: • Century, Crenshaw, Backspin, Providence

  21. Species of turfgrasses can segregate into biotypes that differ in susceptibility to the dollar spot fungus - as in this stand of Penncross creeping bentgrass.

  22. Less susceptible biotype of bentgrass Highly susceptible biotype

  23. Management of Dollar Spot Cultural Management • Reduce shade and increase air circulation to enhance • drying of turf leaves. • Increase N fertilization – High N turf is less susceptible • to dollar spot. • Reduce thatch – Thatch leads to nutrient and drought • stress that increases susceptibility to dollar spot. • Avoid drought stress • Avoid irrigation in late afternoon and early evening - • leaf wetness at night enhances fungal growth.

  24. Management of Dollar Spot Chemical Management

  25. Management of Dollar Spot Chemical Management Contact fungicides registered for dollar spot control chlorothalonil mancozeb thiram PCNB 10 to 14 days control

  26. Management of Dollar Spot Chemical Management Localized penetrant fungicides registered for dollar spot dicarboximides -10 to 21 days control iprodione vinclozolin pyraclostrobin- strobilurin – 14 days control

  27. Management of Dollar Spot Chemical Management Acropetal penetrant fungicides registered for dollar spot propiconazole triadimefon mycobutanil fenarimol tetraconazole triticonazole DMI fungicides 21+ days control boscalid – carboximide 14-21 days control thiophanate-methyl – benzimidazole 21+ days control

  28. Fungicide Resistant Dollar Spot Populations of Sclerotinia homoeocarpa resistant to DMI and benzimidazole fungicides have been detected in several states including GA. Populations resistant to dicarboximide fungicides have been found in a few states.

  29. A lab test to detect resistance in the dollar spot fungus to propiconazole. The resistant isolate (S089) grows on media amended with the fungicide. The other isolates (S084 & S096) do not grow well.

  30. How do we deal with fungicide resistance after it has occurred? Unfortunately, fungicide resistance problems often persist for years because resistant strains continue to survive and cause disease even when the suspect fungicide is no longer used. Therefore, the best strategy is to prevent resistant strains from becoming dominant in turf areas by following these tips…

  31. How to Avoid Fungicide Resistance • Use fungicides as infrequently as possible.

  32. How to Avoid Fungicide Resistance • Use fungicides as infrequently as possible. • 2. Avoid repeated use of fungicides that are • in the same chemical class.

  33. How to Avoid Fungicide Resistance • Use fungicides as infrequently as possible. • 2. Avoid repeated use of fungicides that are • in the same chemical class. 3. Tank-mix ‘at risk’ fungicides with ‘low risk’ fungicides.

  34. ‘AT RISK’ FUNGICIDES FOR RESISTANCE DEVELOPMENT TO DOLLAR SPOT ClassFungicide Examples benzimidazoles* thiophanate-methyl triazoles* propiconazole, triadimefon, myclobutanil pyrimidines* fenarimol dicarboximides+ iprodione, vinclozolin carboximides* boscalid DMIs *Acropetal penetrant +Localized penetrant

  35. Unfortunately, chlorothalonil is the only fungicide that is ‘low risk’ for fungicide resistance and highly effective on dollar spot. Therefore, ‘high risk’ fungicides should be tank-mixed with chlorothalonil.

  36. How to Avoid Fungicide Resistance • Use fungicides as infrequently as possible. • 2. Avoid repeated use of fungicides that are • in the same chemical class. 3. Tank-mix ‘at risk’ fungicides with ‘low risk’ fungicides. 4. Spray preventively to limit size of pathogen population.

  37. High pathogen populations have a greater probability of containing mutant fungicide-resistant strains than low populations. The chance of any particular mutant being in a population is approx. 1 in 100 million. Therefore, the chance of a particular mutation being present in a population increases proportionally to the number of individuals within the population. Think of each dollar spot an individual member of a population.

  38. How are the mutant (fungicide resistant) strains distinguished from the non-mutant (fungicide sensitive) strains?

  39. Apply a fungicide on a high population of an actively growing pathogen and …

  40. the senstive strain will be suppressed, but the resistant strain will not

  41. End of dollar spot section

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