Detection, Monitoring and Management of Rhizoctonia solani AG 2-2 LP That Causes Large Patch in Zoysiagrass in Texas

Zoysiagrass (Zoysia Willd.) is among the most economically important warm-season turfgrasses produced and managed by the green industry. Its use is increasing throughout the southern United States due to superb characteristics and low requirement for cultural inputs. But a primary limitation is its susceptibility to large patch (LP), caused by the soil-borne fungus Rhizoctonia solani anastomosis group (AG) 2-2 LP. Knowledge is lacking concerning the effects of summertime cultural management and environmental conditions on R. solani AG 2-2 LP activity and LP symptom development in zoysiagrass in the fall and spring, particularly in Texas. Thus, thatch/soil moisture, thatch/soil temperature, air temperature, irrigation and nitrogen levels, and chemical control were among environmental and cultural variables evaluated in field and laboratory studies in conjunction with turfgrass quality, fungal activity and disease development. A toothpick baiting method developed to detect Rhizoctonia spp. in other crop systems was modified in this study for use in turfgrass. A semi-selective medium was also developed in this study to aid in isolating R. solani AG 2-2 LP. These studies demonstrated that thatch/soil moisture, thatch/soil temperature and air temperature are significant environmental factors affecting R. solani AG 2-2 LP activity. Irrigation levels correlated with turfgrass quality, thatch/soil moisture, thatch/soil temperature, fungal activity and disease development, but only during certain sampling/rating dates. Nitrogen levels correlated with turfgrass quality, thatch/soil temperature and disease development, but also only during certain sampling/rating dates. These studies also demonstrated that turfgrass quality is acceptable and LP symptom development is minimized when zoysiagrass is irrigated at 36% to 60% of historical reference evapotranspiration and fertilized at an annual rate of 49 kg ha-1. Chemical control of LP in zoysiagrass was inconsistent within and between study years. Fungicides varied in their residual activity, and differences in their effect on R. solani AG 2-2 LP activity and LP symptom development were significant only during certain sampling/rating dates. The toothpick baiting method, used in conjunction with monitoring of environmental conditions, can be a useful tool to predict R. solani AG 2-2 LP activity prior to LP symptom development and to determine the optimal time to apply fungicides preventatively