Bermudagrass Decline/Take-All Root Rot

1. Bermudagrass Decline/Take-All Root Rot caused by Gaeumannomyces graminis var. graminis

2. Knowledge Requirements • What are the best diagnostic signs and symptoms of Bermudagrass Decline/ • Take-All Root Rot (BD/TRR)? • Is the pathogen a spore-former or a non-spore-former? • How does the pathogen infect turfgrass plants? What kills plants infected • with the BD/TRR pathogen? • 4. What species of turfgrasses are susceptible? • 5. What effects do nutrients such as N, P & K have on the disease? • 6. What environmental conditions are required for BD/TRR to develop? • 7. What species of turfgrass are resistant or immune to BD/TRR? • 8. What turf nutrients suppress BD/TRR? • 9. In what ways can the environment and turfgrass be manipulated to suppress • BD/TRR? • 10. Name a fungicide that will control BD/TRR? • During what season(s) are preventive applications of BD/TRR fungicides • applied in GA?

3. Bermudagrass Decline and Take-All Root Rot are the same disease. Unfortunately, the disease was first observed on bermudagrass and named Bermudagrass Decline. A few years later, the disease was found on other warm season grasses. Of course, it would be silly to call a disease Bermudagrass Decline when it occurs on St. Augustinegrass or centipedegrass. Therefore, the name Take-All Root Rot was borne. This is a perfect example of why it is a bad idea to name a disease after the host species on which it is initially observed.

4. Gaeumannomyces graminis var. graminis • Spore-forming fungus. Disseminated by spores or by • mycelium in root tissue. • Survives in previously infected root tissue. • Infection of new roots may occur at soil temperatures as • high as 85°F. • - Fungus colonizes root cortex and vascular system.

5. Bermudagrass Decline/Take-All Root Rot Susceptible Grasses • Bermudagrass Decline occurs on bermudagrass • Take-All Root Rot occurs on St. Augustinegrass, • centipedegrass and probably on other warm • season species.

6. Bermudagrass Decline/Take-All Root Rot Favorable Environment • Hot (>85F), wet conditions are favorable • for infection. • In Georgia, symptoms are observed in mid- • summer to early fall. Root infection probably • takes place several weeks before foliar • symptoms are observed. • Symptoms are most severe when mowing • height is low, soil pH is high, thatch is thick • and turf is subjected to compaction and wear.

7. stele cortex Healthy Bermudagrass root. Note root hairs and absence of dark color in cortex and stele. root hair Root suffering from Bermuda- grass decline/Take-All Root Rot. Note absence of root hairs, darkening of stele, and sloughing of cortex.

8. Dark runner hyphae of Ggg on roots is another diagnostic feature of Bermudgrass Decline/Take- All Root Rot. But the best diagnostic feature is the dark discoloration of the vascular system in roots. Similar to what happens to roots infected with Spring Dead Spot fungus.

9. Chlorosis of leaves from the tip down is the only foliar symptom of Bermudagrass Decline/Take-All Root Rot

10. Dark color of stolons and roots is a good diagnostic symptom of Bermudagrass Decline/ Take-All Root Rot. Healthy Roots Note dark lesion on root.

11. Symptomless St. Augustinegrass roots Necrosis of St. Augustine stolon and roots associated with Take- All Root Rot. Note that necrosis is limited to top 1-2 inches of root zone. Fungus invades most roots near the soil surface.

12. Low mowing heights, high pH, compaction, wear and thatch accumulation enhance symptoms of Bermudagrass decline/Take-All Root Rot.

13. Some bermudagrass cultivars may segregate into biotypes that are resistant to the decline fungus.

14. Excessive thatch accumulation from a green suffering from Bermudagrass Decline

15. Management of Bermudagrass Decline/Take-All Root Rot

16. Management of Bermudagrass Decline/Take-All Root Rot Resistant Species and Cultivars • No bermudagrass cultivars are known to be • resistant. Although, some cultivars may • segregate into resistant biotypes. • Zoysiagrass may be more resistant than other • warm season grasses.

17. Management of Bermudagrass Decline/Take-All Root Rot Cultural Management • Promote optimum root development during the • growing season. Follow the following procedures…

18. Practices That Promote Optimum Root Growth in Bermudagrass • Apply 0.5-1.0 lb. N/1000 sq.ft./month from • late spring to early fall.

19. Practices That Promote Optimum Root Growth in Bermudagrass • Apply 0.5-1.0 lb. N/1000 sq.ft./month. • 2. Have root zone tested annually for available • P, K and minor elements. Moderate to high • levels of Mn and Zn are important for • suppression of Bermudagrass Decline.

20. Practices That Promote Optimum Root Growth in Bermudagrass • Apply 0.5-1.0 lb. N/1000 sq.ft./month. • 2. Have root zone tested annually for available • P, K and minor elements. Moderate to high • levels of Mn and Zn are important for • suppression of Bermudagrass Decline. • 3. Aerify every 3-4 wks during growing season • to supply oxygen to roots.

21. Practices That Promote Optimum Root Growth in Bermudagrass • Apply 0.5-1.0 lb. N/1000 sq.ft./month. • 2. Have root zone tested annually for available • P, K and minor elements. Moderate to high • levels of Mn and Zn are important for • suppression of Bermudagrass Decline. • 3. Aerify every 3-4 wks during growing season • to supply oxygen to roots. • 4. Verticut and topdress every 3-4 wks to • suppress thatch.

22. Practices That Promote Optimum Root Growth in Bermudagrass • Apply 0.5-1.0 lb. N/1000 sq.ft./month. • 2. Have root zone tested annually for available • P, K and minor elements. Moderate to high • levels of Mn and Zn are important for • suppression of Bermudagrass Decline. • 3. Aerify every 3-4 wks during growing season • to supply oxygen to roots. • 4. Verticut and topdress every 3-4 wks to • suppress thatch. • 5. Decrease shade and increase air circulation.

23. Management of Bermudagrass Decline/Take-All Root Rot Cultural Management • Promote optimum root development during the • growing season. • Avoid lime. High pH is conducive for growth • of the decline fungus.

24. Management of Bermudagrass Decline/Take-All Root Rot Cultural Management • Promote optimum root development during the • growing season. • Avoid use of lime. High pH is conducive for • growth of decline fungus. • Use ammonium-based nitrogen fertilizers to • reduce pH of thatch and soil. The decline fungus is • sensitive to pH < 6.3. • - Prevent thatch from exceeding thickness of 0.5 in.

25. Management of Bermudagrass Decline/Take-All Root Rot Chemical Control • No fungicides registered. • axoxystrobin (Heritage) and thiophanate- • methyl (Cleary’s 3336, SysTec 1998, T-Storm, etc.) • may be effective at high label rates. • Must apply preventively. Once you see • foliar symptoms it’s too late. • Begin applications about 3-4 wks after spring • green-up. Continue at 3-4 wk intervals.

26. Management of Bermudagrass Decline/Take-All Root Rot Chemical Control • Good idea to tank mix azoxystrobin or thiophanate- • methyl with either chlorothalonil (Daconil) or • mancozeb (Fore). This will decrease the • probability of resistance developing to these high • risk fungicides.

27. End of Bermudagrass Decline Section