Brown patch is caused by the fungus Rhizoctonia solani. It is the most widespread of all turf diseases, occurring throughout the world and attacking all known turfgrass species. The disease appears as a blight in circular patches ranging in size from a few inches to several feet. A dark purple to grayish-brown border ("smoke ring") may appear at the margins of patches, especially in periods of high humidity. The smoke ring effect is most common on close-cut (≤1”) turf such as golf greens, appearing infrequently on higher cut turf such as fairways and lawns. White aerial mycelium may be observed under humid conditions. Irregular lesions with purplish to brown borders and tan centers are observed on leaves of high cut turf, and affected leaves eventually turn brown and dry out. Distinct lesions may not occur on low cut turf, and leaves may simply turn brown and die back. If conditions remain conducive to disease, large areas of turf may rapidly become infected. Although leaves in blighted area are usually killed, a return to cooler weather enables regrowth from crowns, stolons, or rhizomes. Crowns are rarely killed. Brown to black sclerotia are sometimes found beneath the leaf sheath or on the crowns.
R. solani and other Rhizoctonia species are natural inhabitants of the soil. R. solani becomes active when soil temperatures reach into the 60s (>15.5°C), but it does not parasitize the grass until air temperatures rise into the mid-80s (28-30°C) with high humidity and nighttime temperatures above 65°F (18°C). When the grass plant suffers heat stress and high temperature growth cessation, the disease progresses rapidly. Dense, highly fertilized, and frequently watered turf is most susceptible to infection.
Practices that can reduce disease incidence include:
- Avoid excessive nitrogen applications. Slow release forms of nitrogen are beneficial.
- Improve subsurface and surface drainage.
- Reduce leaf wetness by manual removal of dew.
- Improve air circulation and light penetration by pruning trees and shrubs.
- Mechanically remove thatch if it accumulates to more than 0.5 inch.
- Plant disease tolerant cultivars.
In the case of brown patch, it is often helpful to use weather-based forecasting models to time preventive fungicide applications. A curative fungicide program during the summer stress period is not recommended for higher cut turf because disease development is rapid and the ability of the turf to recover is limited. Recovery should be observed when cooler temperatures slow fungal growth and encourage turf growth. On golf greens, consider combination products or tank mixes, especially if that area has a history of dollar spot.
For a listing of fungicides currently labeled for management of this disease, please refer to the Professional Guide for IPM in Turf for Massachusetts.