Yellow Patch or Cool Season Brown Patch (Rhizoctonia cerealis)
Yellow patch (caused by Rhizoctonia cerealis) was observed this past weekend at a Boston area golf course during a visit. Yellow patch commonly occurs on Poa and Agrostis turfgrass species is most commonly observed in the Spring and Fall. Symptoms typically appear as yellow or brownish rings or arcs and patches on putting greens (symptoms may appear more diffused on taller cuts of turf) (Fig. 1A and 1B). Rings or patches range from 6 inches to 3 feet in diameter and may appear irregularly shaped if multiple patches or rings coalesce. Annual bluegrass seems to be the most susceptible (Fig. 2A). Creeping bentgrass appears to be more susceptible to the disease than velvet bentgrass (Fig. 2B). Temperatures between 50-65°F during cloudy or wet periods are most conducive to disease development. However, temperatures below 45°F or dry, sunny conditions with temperatures above 75°F will interrupt disease development.
Golf course putting greens with poor drainage, excessive thatch and shade are more likely to have problems with yellow patch. Excessive applications (>0.25 lb N/1,000 ft2) of water-soluble nitrogen (WSN) in the spring have been shown to encourage disease development, and therefore should be avoided. Springtime nitrogen can be applied as a slow release fertilizer and should not exceed 0.25 lb N/1,000 ft2. Preventative fungicide applications are the most effective means for controlling yellow patch, especially if yellow patch has been a problem in the past. Fungicides from the strobilurin, SDHI (flutolanil), and DMI classes are effective choices for control and more information on which active ingredients are labeled for yellow patch can be found in our chart, 'Commonly Used Turfgrass Fungicides and the Diseases they are Labeled to Control'. Curative fungicide applications will prevent further infection, however, turfgrass recovery is dependent on favorable growing conditions. Since the pathogen is active during very specific environmental conditions, the best course of action for sites with adequate drainage and sunlight is to allow warmer temperatures and sunlight to aid in turfgrass recovery. If you have questions about fungicide selections for yellow patch control, please contact the Turfgrass Pathology Lab (turf@psis.umass.edu or 413-577-3303).
