Presentation on theme: "Large Patch. 1.What are the best diagnostic signs and symptoms of large patch? 2.Is the pathogen a spore-former or a non-spore-former? 3.How does the."— Presentation transcript:
1.What are the best diagnostic signs and symptoms of large patch? 2.Is the pathogen a spore-former or a non-spore-former? 3.How does the pathogen survive adverse conditions? 4.How does the pathogen infect turfgrass plants? 5.What species of turfgrasses are susceptible? 6.What effects do nutrients such as N, P & K have on the disease? 7.What environmental conditions are required for large patch to develop? 8. What species of turfgrass are resistant or immune to large patch? 9. What turf nutrients suppress large patch? 10. In what ways can the environment be manipulated to suppress large patch? 11. Name a contact, systemic and penetrant fungicide that will control large patch. 12. During what season(s) are preventive applications of large patch fungicides applied in GA? Knowledge Requirements
BROWN PATCH Rhizoctonia Large Patch Warm Season Grasses Rhizoctonia solani (strain AG 2-2 LP) Brown Patch Cool Season Grasses Rhizoctonia solani (strains AG 1 and AG 2-2IIIB) Yellow Patch Cool Season Grasses Rhizoctonia cerealis What was once consider one disease (Brown Patch) in now considered as three. In this section we will review Large Patch.
RHIZOCTONIA LARGE PATCH Rhizoctonia solani (strain AG 2-2 LP) caused by
Rhizoctonia solani (strain AG 2-2 LP) - Nonspore-forming fungus. - Survives as sclerotia or dormant mycelium in thatch, soil or dead tissue. - Initial infection occurs on leaf sheaths when night temps at 40-60°F and crowns of plants have been wet for more than 10 hrs. Note how Large Patch occurs at a lower temp. than Brown Patch
RHIZOCTONIA LARGE PATCH Susceptible Grasses All warm season grasses. Note that large patch occurs only on warm season grasses while brown patch occurs on cool season grasses.
RHIZOCTONIA LARGE PATCH Favorable Environment - Night temps <60°F. - High soil moisture. - More than 10 hr. of crown and stolon wetness per day for several days. Lower temp. than brown patch
Large patch on St.Augustinegrass – Patches can be 15 or more ft. in diameter. About 8 ft. in diameter
Large patch on hybrid bermudagrass. Symptoms occur in the spring and fall when the turf is either coming out of dormancy or going into dormancy.
Large patch on zoysiagrass. Note how disease does not spread to perennial ryegrass at top of photo. Perennial rye, a cool-season grass, is not susceptible to the strain of of R. solani that causes Large Patch. Large patch on zoysia perennial rye
Large patch on hybrid bermudagrass Large patch on a zoysiagrass fairway Outer margins of patches are yellow to orange in color when the large patch fungus is actively growing and infecting turf.
Large patch on recently sodded zoysia lawn.
Large Patch on zoysia. Note how weeds develop in center of patch. Note orange border indicating active disease development. Large Patch on St. Augustinegrass.
Large patch beginning to develop on zoysia in the fall. Patches (<1 ft. in diam.) of yellow-orange leaves are an indication of early infection. As patches increase in size, leaves in the center of the patch turn gray. Look at leaf sheaths to make diagnosis
Development of brown lesions on leaf sheaths is the best diagnostic symptom of large patch Note lesions on this leaf sheath of St. Augustine. This is where the fungus is infecting. No lesions on leaves.
Lesion forms on leaf sheath, not on leaf. Leaf turns yellow due to poor translocation of nutrients and water up through leaf sheath.
Lesions often coalesce to consume whole leaf sheaths Note how lesions do not form on leaves, just on leaf sheaths. This is a difference between large patch and brown patch.
Fungus rots leaf sheaths and leaves shrivel and die do to poor translocation of water and nutrients. Fungus seldom grows past ligule and into the leaf. ligule
Lesion on leaf sheath of centipedegrass
Dark lesion on outer leaf sheath of zoysiagrass When outer leaf sheath is stripped away, inner lesion may appear bleached.
MANAGEMENT OF RHIZOCTONIA LARGE PATCH
MANAGEMENT OF RHIZOCTONIA LARGE PATCH Cultural Management - Avoid N fertility in spring prior to mid-May and in fall after Sept. 1st. - Maintain moderate to high P & K according to soil test. - Decrease shade and increase air circulation. - Improve soil drainage. - Avoid irrigation in late afternoon and in evening prior to midnight. - Maintain thatch at ½ inch or less.
MANAGEMENT OF RHIZOCTONIA LARGE PATCH Resistant Species and Cultivars - All warm season species are susceptible, but in in general, bermudagrass will recover faster than either zoysia, St. Augustine, pasalum or centipede. - No cultivars are known to be resistant.
Management of Large Patch Chemical Control Contact fungicides – chlorothalonil, mancozeb, thiram, polyoxin. 14 days control Localized penetrants – iprodione, vinclozolin, trifloxystrobin, pyraclostrobin. 21 days control Acropetal penetrants – azoxystrobin, flutolanil, thiophanate-methyl, propiconazole, triadimefon, fenarimol. 21-28 days control
Management of Large Patch Chemical Control Preventive or early curative* fungicide applications are recommended in spring and fall when night temperatures are between 35 and 60°F. *when patches are less than softball size.