Presentation on theme: "An Introduction to Root Diseases. Introduction to Root Diseases (some general comments) 1.Root diseases are more difficult to diagnose than foliar diseases."— Presentation transcript:
Introduction to Root Diseases (some general comments) 1.Root diseases are more difficult to diagnose than foliar diseases. Examination of foliage is of minor importance in diagnosis of root diseases. Roots must be washed and examined.
Introduction to Root Diseases (some general comments) 1.Root diseases are more difficult to diagnose than foliar diseases. Examination of foliage is of minor importance in diagnosis of root diseases. Roots must be washed and examined. 2.With most root diseases, roots are severely diseased by the time foliar symptoms are expressed. Therefore, waiting until foliar symptoms develop is often too late to achieve successful control of root diseases.
Introduction to Root Diseases (some general comments) 1.Root diseases are more difficult to diagnose than foliar diseases. Examination of foliage is of minor importance in diagnosis of root diseases. Roots must be washed and examined. 2.With most root diseases, roots are severely diseased by the time foliar symptoms are initially expressed. Therefore, waiting until foliar symptoms develop is often too late to achieve successful control of root diseases. 3.Successful preventive control of root diseases must begin weeks or months before foliar symptoms are expected to develop. Therefore, knowledge of past root disease development on a turf area is essential.
Root Diseases of Warm Season Grasses - Spring Dead Spot - Take-All Root Rot/Bermudagrass Decline Root Diseases of Cool Season Grasses - Take-All Patch - Pythium Root Rot - Summer Patch Root Diseases of Warm and Cool Season Grasses - Fairy Ring - Diseases incited by nematodes Some Important Root Diseases of Turfgrasses
Knowledge Requirements 1.What are the best diagnostic signs and symptoms of Spring Dead Spot (SDS)? 2.Is the pathogen a spore-former or a non-spore-former? 3.How does the pathogen infect turfgrass plants? What kills plants infected with the SDS 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 SDS to develop? 7. What species of turfgrass are resistant or immune to SDS? 8. What turf nutrients suppress SDS? 9. In what ways can the environment and turfgrass be manipulated to suppress SDS? 10. Name a fungicide that will control SDS? 11.During what season(s) are preventive applications of SDS fungicides applied in GA?
Spring Dead Spot Ophiosphaerella korrae* Ophiosphaerella herpotricha Ophiosphaerella narmari caused by: *O. korrae is a common cause of SDS is the eastern U.S. The other species are more common in mid-western states.
Ophiosphaerella Species - Spore-forming fungi. - Survive as mycelium in roots. - Root infection takes place at 50-70°F in the fall via hyphopodia. Hyphopodia are infection structures similar to appressoria, but rather than arising from germinating spores, hyphopodia are formed at the ends of hyphae that grow along root surfaces.
Hyphopodia. Lobed infection structures formed by hyphae that grow along the surface of roots.
Ophiosphaerella Species - The Ophiosphorella species that cause spring dead spot colonize the root cortex and vascular system. - Infection of bermudagrass roots in the fall makes the infected plants more sensitive to low-temperature kill during the winter. The fungus does not kill the turf directly, it predisposes the turf to winter kill. Therefore, in the southeast U.S., severe spring dead dead spot is usually observed only in areas that are exposed to temps. <20°F for approx. ten days or more during the winter.
Spring Dead Spot Susceptible Grasses - Bermudagrass hybrids in U.S. and Australia. - St. Augustinegrass – Australia - Zoysiagrass – U.S. and Japan.
Spring Dead Spot Favorable Environment - Warm fall weather – Temps. >50°F in September, October, and November – infection of roots occurs at this time - Followed by cold winters - <20°F for extended periods – Infected plants die of winter kill, non-infected plants survive - Disease is severe in compact soil with pH >6.3
Spring Dead Spot Straw-colored patches up to 2 ft. in diameter are observed after green-up of bermudagrass in spring.
Spring dead spot can be severe on hybrid bermudagrass like Tif419.
Spring Dead Spot on a bermudagrass golf green Regrowth of turf is very slow. Bare patches may linger until July or longer.
Dead spots often coalesce resulting in large irregular patches. However, the best diagnositic feature of SDS is not found above ground. You have to look at roots.
Roots of affected bermudagrass turn dark-brown to black. This is the best diagnostic symptom of spring dead spot. Samples taken from the margin of circular, straw- colored patches of bermudagrass in spring.
Spring dead spot patches are often invaded by common bermudagrass, crabgrass or broad-leaf weeds
Resistant Species and Cultivars - Common (non-hybrid) bermudagrass and other warm season grass species are less susceptible than hybrid bermudagrass. - The bermudagrass cultivars, Guymon, Sundevil, Midlawn, Midfield, Ft. Reno and Mirage exhibit low to moderate susceptibility.
Spring Dead Spot Management Cultural Management - Reduce N applications in late summer and fall. High fall N can delay dormancy and increase chances of winter kill. - Use ammonium-based nitrogen fertilizers to reduce pH of thatch and soil. Ophiosphorella spp. do not grow well at pH < 6.3. - Maintain moderate to high amounts of soil K to promote tolerance to winter kill. - Reduce thatch and soil compaction to promote good root growth.
Spring Dead Spot Management Chemical Control - propiconazole, thiophanate-methyl, fenarimol, azoxystrobin and myclobutanil are registered for control of SDS. Best results are achieved with fenarimol (Rubigan). - applications must be made in fall (early Oct. to early Nov. in Georgia). Best control achieved with 1-3 applications 3-4 wks apart.
Table 1. Effect of Fungicides on Spring Dead Spot of Tift Dwarf Bermudagrass at Griffin, GA - 2006 TreatmentIntervalRate x Spots/plotSpots/5,000 sq.ft. No fungicide--4.01239 Rubigan 1.0A.S.1 appl6.0 fl.oz.0.5* y 155 Rubigan 1.0A.S.2 appl (28 day)4.0 fl.oz.1.8*558 Banner MAXX 1.3ME 1 appl4.0 fl.oz.1.5*465 Banner MAXX 1.3ME 2 appl (28 day)4.0 fl.oz.1.5*465 Eagle 40WSP1 appl1.2 oz.2.3713 Eagle 40WSP2 appl (28 day)1.2 oz.2.5774 x Listed as ounces of product per 1000 sq.ft. unless indicated otherwise. y Values followed by an asterisk (*) are significantly different from the non-treated check at α = 0.05. Results of a trial designed to assess effects of fungicides on SDS