2Knowledge Requirements What are the best diagnostic signs and symptoms of large patch?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 turfgrasses are susceptible?What effects do nutrients such as N, P & K have on the disease?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 suppresslarge patch?11. Name a contact, systemic and penetrant fungicide that willcontrol large patch.12. During what season(s) are preventive applications of large patchfungicides applied in GA?
3What was once consider one disease (Brown Patch) in now considered as three. In this section we will review Large Patch.BROWN PATCHBrown PatchCool Season GrassesRhizoctonia solani(strains AG 1 andAG 2-2IIIB)Rhizoctonia Large PatchWarm Season GrassesRhizoctonia solani(strain AG 2-2 LP)Yellow PatchCool Season GrassesRhizoctonia cerealis
4RHIZOCTONIA LARGE PATCH caused byRhizoctonia solani(strain AG 2-2 LP)
5(strain AG 2-2 LP) Rhizoctonia solani Nonspore-forming fungus. Survives as sclerotia or dormant myceliumin thatch, soil or dead tissue.Initial infection occurs on leaf sheaths whennight temps at 40-60°F and crowns ofplants have been wet for more than 10 hrs.Note how Large Patch occurs at a lower temp. than Brown Patch
6RHIZOCTONIA LARGE PATCH Susceptible GrassesAll warm season grasses.Note that large patch occurs only on warm season grasses while brown patchoccurs on cool season grasses.
7RHIZOCTONIA LARGE PATCH Favorable EnvironmentNight temps <60°F.High soil moisture.More than 10 hr. of crown and stolonwetness per day for several days.Lower temp. thanbrown patch
8Large patch on St.Augustinegrass – Patches can be About 8 ft. in diameterLarge patch on St.Augustinegrass – Patches can be15 or more ft. in diameter.
9Large patch on hybrid bermudagrass. Symptoms occur in the spring and fallwhen the turf is either coming out ofdormancy or going into dormancy.
10Large patch on zoysiagrass. Note how disease does not perennial ryeLarge patch on zoysiagrass.Note how disease does notspread to perennial ryegrassat top of photo. Perennial rye,a cool-season grass, is notsusceptible to the strain ofof R. solani that causes LargePatch.Large patch on zoysia
11Large patch on hybrid bermudagrass Outer margins of patches areyellow to orange in color whenthe large patch fungus is activelygrowing and infecting turf.Large patch on a zoysiagrass fairway
13Large Patch on zoysia. Note how weeds develop in center of patch.Note orange border indicating activedisease development.Large Patch on St. Augustinegrass.
14Large patch beginning to develop on zoysia in the fall. Patches (<1 ft. in diam.) of yellow-orange leaves arean indication of early infection. As patches increase insize, leaves in the center of the patch turn gray.Look at leaf sheaths to make diagnosis
15No lesions onleaves.Note lesions onthis leaf sheathof St. Augustine.This is wherethe fungus isinfecting.Development ofbrown lesions onleaf sheaths is thebest diagnosticsymptom of largepatch
16Leaf turns yellow due to poor translocation of nutrients and waterup through leaf sheath.Lesion forms on leafsheath, not on leaf.
17Lesions often coalesce to consume whole leaf sheaths Note how lesions do not form onleaves, just on leafsheaths.This is a differencebetween large patchand brown patch.Lesions oftencoalesce toconsume wholeleaf sheaths
18liguleFungus rots leaf sheaths and leaves shrivel and die do to poor translocation ofwater and nutrients. Fungus seldom grows past ligule and into the leaf.
22RHIZOCTONIA LARGE PATCH MANAGEMENT OFRHIZOCTONIA LARGE PATCHCultural ManagementAvoid N fertility in spring prior to mid-May and in fallafter Sept. 1st.- Maintain moderate to high P & K accordingto soil test.Decrease shade and increase air circulation.- Improve soil drainage.Avoid irrigation in late afternoon and inevening prior to midnight.- Maintain thatch at ½ inch or less.
23RHIZOCTONIA LARGE PATCH MANAGEMENT OFRHIZOCTONIA LARGE PATCHResistant Species and CultivarsAll warm season species are susceptible, but inin general, bermudagrass will recoverfaster than either zoysia, St. Augustine, pasalumor centipede.- No cultivars are known to be resistant.
24Management of Large Patch Chemical ControlContact fungicides – chlorothalonil, mancozeb,thiram, polyoxin. 14 days controlLocalized penetrants – iprodione, vinclozolin,trifloxystrobin, pyraclostrobin. 21 days controlAcropetal penetrants – azoxystrobin, flutolanil,thiophanate-methyl, propiconazole, triadimefon,fenarimol days control
25Management of Large Patch Chemical ControlPreventive or early curative* fungicide applications are recommended inspring and fall when night temperatures are between 35 and 60°F.*when patches are less than softball size.