Brown patch was diagnosed in the UMass Extension Plant Diagnostic Lab last week on a sample from a lawn. Caused by the fungus Rhizoctonia solani, brown patch thrives in the hot, humid weather of mid-summer. All types of cool season turf are susceptible to this disease, though in general Kentucky bluegrass is less susceptible than ryegrass or fescues.
Rhizoctonia is a natural inhabitant of the soil and thatch and may begin to infect turf when soil temperatures exceed 70°F. As air temperatures rise into the mid 80’s with high humidity and nights above 65°F, symptoms develop as turf begins to suffer from heat stress and growth stops. Tan, irregular leaf spots with reddish-brown borders will appear on leaves, and leaf blades may eventually die back. Fuzzy white mycelium may be observed on the turf early on humid mornings. Patches of affected grass can range from 2 inches to 2 feet in diameter. Unlike many other turf pathogens, Rhizoctonia does not produce airborne spores.
- Use good cultural practices to minimize turf stress in any way possible.
- Excess nitrogen enhances disease frequency and severity; avoid high nitrogen levels (especially in mid-summer), but maintain adequate potassium and phosphorous to enhance plant resistance.
- Reduce thatch: an excessive thatch layer (1/3 to 1/2 inch or greater) is one of the most common factors contributing to turf stress and disease development.
- Good drainage is essential to reduce humidity within the turf canopy; aerate or use other practices to improve soil drainage.
- Water deeply and infrequently (about 1" per week in the absence of rain) to encourage deep rooting and reduce humidity in the turf canopy.
- Increase air circulation and sun exposure by pruning shrubs and trees.
- Fungicide application on lawns during mid-summer is discouraged because of the potential for rapid disease development and poor recuperative ability of the turf. Some time will pass before improvement is observed; recovery will not occur until cooler temperatures arrive.
- Minimize herbicide and insecticide applications during an outbreak as they may enhance brown patch activity.
If the problem becomes significant, consider overseeding or re-planting with less susceptible turf cultivars: see the Turfgrass Selection: Species and Cultivars chapter of UMass Extension's Professional Guide for IPM in Turf and http://www.ntep.org for information.
Submitted by: Dr. Angela Madeiras