Tech Notes Issue 16
On Warm Season Turfgrasses, Large Patch is Often Prevalent under Springtime Conditions
Large Patch is an early - mid spring disease of warm season turfgrasses. First reported on zoysiagrass, the disease was initially named Zoysia patch. After the pathogen was identified on numerous warm season turfgrasses, the common name "Large Patch" evolved. Although most severe on zoysiagrass, large patch is increasingly becoming more prevalent on seashore paspalum.
The pathogen Rhizoctonia solani is similar to the pathogen that causes brown patch on cool season turfgrasses, except the large patch pathogen belongs to a different anastomosis group (AG-2-2 (LP). The optimal temperature for infection is 25-28C but can infect at temperatures ranging from 10 to 30 C. Generally, large patch is most severe under moist or wet conditions.
Cultural practices that minimize surface moisture will help reduce the severity of large patch. Prolonged periods of fog or dew enhance the severity of this disease. Although, eliminating fog is beyond our management abilities, reducing dew periods through dragging, poling or lightly syringing will decrease disease severity. During winter and early spring maintain moderate to low nitrogen levels during periods when Rhizoctonia is active.
Fungicides are available that will control Large patch. In general preventative treatments are more effective than therapeutic (curative) treatments.
(Above left) Large patch symptoms on zoysiagrass. The symptoms often appear as the turf is breaking winter dormancy. (Centre) Large patch symptoms on most warm season turfgrasses appear as a whitish color and rather large areas are affected. (Above right) Large patch is becoming more of a common disease of seashore paspalum. The picture below was taken on a ‘SeaDwarf’ seashore paspalum fairway.