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 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 PatchWarm Season GrassesRhizoctonia solani(strain AG 2-2 LP)

Brown PatchCool Season GrassesRhizoctonia solani(strains AG 1 and AG 2-2IIIB)

Yellow PatchCool Season GrassesRhizoctonia 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 PATCHSusceptible Grasses

All warm season grasses.

Note that large patch occurs only on warm season grasses while brown patchoccurs on cool season grasses.

RHIZOCTONIA LARGE PATCHFavorable Environment

- Night temps <60°F.

- High soil moisture.

- More than 10 hr. of crown and stolon wetness per day for several days.

Lower temp. thanbrown patch

Large patch on St.Augustinegrass – Patches can be15 or more ft. in diameter.

About 8 ft. in diameter

Large patch on hybrid bermudagrass.Symptoms occur in the spring and fallwhen the turf is either coming out of dormancy or going into dormancy.

Large patch on zoysiagrass.Note how disease does notspread to perennial ryegrassat top of photo. Perennial rye,a cool-season grass, is not susceptible to the strain ofof R. solani that causes LargePatch.

Large patch on zoysia

perennial rye

Large patch on hybrid bermudagrass

Large patch on a zoysiagrass fairway

Outer margins of patches areyellow to orange in color whenthe large patch fungus is activelygrowing and infecting turf.

Large patch on recently soddedzoysia lawn.

Large Patch on zoysia. Note howweeds develop in center of patch.

Note orange border indicating activedisease 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 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

Development ofbrown lesions onleaf sheaths is thebest diagnosticsymptom of largepatch

Note lesions onthis leaf sheathof St. Augustine.This is wherethe fungus isinfecting.

No lesions onleaves.

Lesion forms on leaf sheath, not on leaf.

Leaf turns yellow due to poortranslocation of nutrients and waterup through leaf sheath.

Lesions oftencoalesce toconsume wholeleaf sheaths

Note how lesionsdo not form onleaves, just on leafsheaths.This is a differencebetween large patchand brown patch.

Fungus rots leaf sheaths and leaves shrivel and die do to poor translocation ofwater and nutrients. Fungus seldom grows past ligule and into the leaf.

ligule

Lesion on leaf sheathof centipedegrass

Dark lesion on outer leaf sheath of zoysiagrass

When outer leafsheath is strippedaway, inner lesionmay appear bleached.

MANAGEMENT OF

RHIZOCTONIA LARGE PATCH

MANAGEMENT OFRHIZOCTONIA 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 OFRHIZOCTONIA 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 PatchChemical ControlContact 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 PatchChemical 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.

End of Large Patch Section