Ask the expert: Large Patch

An Overly Wet Winter: This has been a winter to remember. Snow has remained in the headlines and some regions saw record amounts. Even parts of the South were covered in snow at times – that sure got our attention! A majority of our soils now remain saturated and a disease of warm-season turf known as large patch is likely to be more active this spring. Golf course superintendents will tell you that large patch, Rhizoctonia solani AG LP, is more obvious than just about any other disease of turf: the resultant patches can exceed 20 feet in diameter.

Symptoms of Large Patch: Affected turf looks thin and sunken, and leaves appear tan or yellow-orange. A useful diagnostic feature is the brilliant “orange firing” of turf along the outer edge of the expanding ring. The actual point of infection by R. solani is lower in the turf canopy: the leaf sheaths. The resultant lesion causes a girdling effect on the stem which looks brown to black.

Conditions: Large patch is most damaging in spring/fall during cool (50-86° F) and overly wet conditions. The primary driver of this disease is saturated soils.

Host Range: Previously, large patch was commonly referred to as zoysia patch. However, R. solani has a relatively wide host range of warm-season turf, which includes bermudagrass, buffalograss, centipedegrass, kikuyugrass, seashore paspalum, St. Augustinegrass, as well as zoysiagrass.

Significance: As we navigate through April and May, large patch can really put the hurt on warm-season turf as its growth and recuperative potential is slow. For golf course superintendents who manage warm-season turf, the timing of large patch could not be worse. Resultant damage can be long lasting and patches can remain visible into early summer.

Prevention: To prevent large patch from getting the upper hand, a combination of practices are used. Cultural practices are very important, as saturated soil conditions exacerbate large patch. Curative fungicides timed in spring can prevent expansion of existing patches and promote recovery. However, data and experience indicate a first fall fungicide application is most important, followed by the second application in the fall, then the third in spring.

Top Five Large Patch Cultural Control Strategies in spring:

• Improve drainage – install drainage tiles (alleviate wet fairway areas)
• Avoid over-irrigation – be judicious in spring (during infection cycle)
• Reduce compaction/thatch – plan for summer aeration (when turf is growing)
• Limit nitrogen – using more than 2 lbs. per 1000 sq. ft. of actual nitrogen in a given season can encourage disease formation
• Use quick release nitrogen – nitrogen by urea can speed turf recovery (late May/early June timing)

Top Five Large Patch Fungicide Strategies in spring:

• Apply by 50 percent green-up of turf – no later for spring fungicide applications
• Plan spring preventive application – suggested for areas with a history of large patch or if large patch is already active
• Plan spring curative application – scout and map affected areas
• Use 2 gal. per1000 sq. ft. of spray volume (minimum) – penetrates to site of infection
• Select appropriate nozzle – nozzle type is important; flat fan nozzles provide good coverage

Reference
http://www.backedbybayer.com/system/white_paper/asset_file/58/SolutionLargePatch_v3.pdf