Anthracnose

1. Anthracnose caused by: Colletotrichum cereale formerly known as C. graminicola

2. Knowledge Requirements • What are the best diagnostic signs and symptoms of anthracnose? • 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 anthracnose to develop? • 8. What species of turfgrass are resistant or immune to anthracnose? • 9. What turf nutrients suppress anthracnose? • 10. In what ways can the environment be manipulated to suppress • anthracnose? • 11. Name a contact and penetrant fungicide that will • control anthracnose. • 12. During what season(s) are preventive applications of anthracnose • fungicides applied in GA?

3. Anthracnose There are two forms of anthracnose Foliar Anthracnose – Most common on annual bluegrass in late spring through summer (>80°F). Basal Rot Anthracnose – Most common on bentgrass in spring under cool (32-50°F) wet conditions. Can continue into summer.

4. Colletotrichum cereale • Spore-forming fungus. • Survives as dormant mycelium and sclerotia. • Fungus infects leaf sheaths, leaves and • occasionally roots. • Infection occurs via germinating sclerotia or • spores at temps >50°F and >10 hrs of leaf or • shoot wetness.

5. Anthracnose Susceptible Grasses • All grasses are susceptible. However, • only annual bluegrass and creeping • bentgrass exhibit severe symptoms.

6. Anthracnose Environmental Factors that Enhance Disease Severity • The anthracnose fungus is a weak pathogen that • generally infects only environmentally stressed • turf. • Factors such as temperature extremes, soil moisture • extremes, low fertility, thatch accumulation, soil • compaction, wear and insect damage predispose • turf to infection by C. cereale.

7. Anthracnose Symptoms (Foliar Anthracnose)

8. From a distance, infected areas of turf appear chlorotic and stunted.

9. Within a few days, many of the chlorotic areas of turf turn reddish brown

10. Leaves associated with chlorotic patches exhibit chlorotic lesions that turn black in the center. This is the best diagnostic symptom of foliar anthracnose.

11. Lesions may be difficult to see on close-cut turf such as golf greens. In this case, necrotic leaves can be examined and…

12. if anthracnose has been present the dead leaves should contain black hair-like hyphae called setae. Setae can be observed easily With a 10X eyepiece.

13. Microscopic examination of setae reveals that they are associated with mounds of spores formed in a gelatinous matrix. The sticky spores can be spread via rain splash, irrigation, turf maintenance equipment, or even foot traffic.

14. Photomicrograph of dark setae and crescent- shape spores of the anthracnose fungus.

15. Spores (conidia) of the anthracnose fungus. Spores have been stained. In nature, they are colorless.

16. Anthracnose Symptoms (Basal Rot Anthracnose)

17. Basal rot anthracnose in a fairway composed of creeping bentgrass (light green) and annual bluegrass (dark green). Note that disease is most severe on the bentgrass.

18. Anthracnose basal rot is common on bentgrass golf greens. It often occurs in patches that correspond to susceptible biotypes of bentgrass.

19. Patches of bentgrass exhibiting basal rot anthracnose surrounded by unaffected annual bluegrass.

20. To diagnose basal rot anthracnose, look for dark discoloration at the base of the grass shoots (tillers). No foliar lesions are present. Leaves die due to girdling of the shoot by the fungus. Microscopic analysis reveals that the discoloration is associated with sclerotia formed by the anthracnose fungus at the base of the leaf sheaths. Sclerotia function in survival (over- wintering) of C. cereale.

21. Sclerotia at higher magnification.

22. Conidia formed on internal leaf sheath of bentgrass. No setae are present. It appears that light is required for setae to form. In the Course Introduction we mentioned that many spore-forming fungi form appressoria to penetrate plant surfaces. These are appressoria formed by the anthracnose fungus.

23. Anthracnose Management

24. Anthracnose Management Disease Resistant Grasses • Conversion from creeping bentgrass or annual • bluegrass to any other species will reduce the • incidence and severity of anthracnose. • Among bentgrass varieties, only Penncross appears • to be highly susceptible to basal rot anthracnose. • Conversion to a variety that is better-adapted to your • climate may reduce problems with anthracnose.

25. Anthracnose – Cultural Management For suppression of anthracnose, most cultural practices are directed toward reducing stress (drought, low fertility, soil compaction, injury) on susceptible grasses.

26. Anthracnose – Cultural Management • Increase frequency of core aerification

27. Anthracnose – Cultural Management • Increase aerification frequency • Increase nitrogen fertility

28. Anthracnose – Cultural Management • Increase aerification frequency • Increase nitrogen fertility • Use light weight mowing equipment

29. Anthracnose – Cultural Management • Increase aerification frequency • Increase nitrogen fertility • Use light weight mowing equipment

30. Anthracnose – Cultural Management • Increase aerification frequency • Increase nitrogen fertility • Use light weight mowing equipment • Limit thatch to ¼ inch or less

31. Anthracnose – Cultural Management • Increase aerification frequency • Increase nitrogen fertility • Use light weight mowing equipment • Limit thatch to ¼ inch or less • Control root- and crown-feeding insects

32. Anthracnose – Cultural Management • Increase aerification frequency • Increase nitrogen fertility • Use light weight mowing equipment • Limit thatch to ¼ inch or less • Control root- and crown-feeding insects • Decrease shade and increase air circulation

33. Anthracnose – Cultural Management • Increase aerification frequency • Increase nitrogen fertility • Use light weight mowing equipment • Limit thatch to ¼ inch or less • Control root- and crown-feeding insects • Decrease shade and increase air circulation • Avoid irrigation in late afternoon and in evening prior to midnight

34. Anthracnose – Chemical Control

35. Fungicides that suppress anthracnose • Contacts – chlorothalonil (Daconil), mancozeb (Fore). • Preventive control only – 10 to 14 days control. • Localized penetrants - trifloxystrobin (Compass) and • pyraclostrobin (Insignia). Preventive control and possibly • curative control – 14 to 21 days control. • Acropetal penetrants – propiconazole (Banner MAXX), triadimefon (Bayleton), myclobutanil (Eagle), fenarimol (Rubigan), azoxystrobin (Heritage) and thiophanate-methyl (Cleary’s 3336). Preventive and curative control – • 21 to 28 days control.

36. Anthracnose control with propiconazole Non-treated check

37. Anthracnose – Chemical Control • Caution !!! When temps are >85F for extended periods, repeated use of DMI fungicides (propiconazole, triadimefon, myclobutanil and fenarimol) may result in detrimental growth regulation effects on bentgrass.

38. Anthracnose – Chemical Control Since 2004, biotypes of the anthracnose fungus that are resistant to benzimidazole and strobilurin fungicides have been detected on golf courses in several states including GA. To limit the probability of fungicide resistance, the same precautions need to be taken with anthracnose fungicides as listed for dollar spot fungicides (see dollar spot section).

39. End of Anthracnose Section