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TECHNICAL SESSION: Chemical Control of Fungal Diseases

Effectiveness of fungicide programs against turfgrass fungal disease leaf and sheath spot (mini ring) on Bermuda grass in Hawaii.
Zhiqiang Cheng - University of Hawaii at Manoa.

Leaf and sheath spot/blight, or mini ring, is a turfgrass fungal disease confirmed in multiple states in USA. The causal pathogen is commonly considered to be Waitea circinata var. zeae, more commonly known as Rhizoctonia Zeae. It can be hosted by both cool- and warm-season turfgrasses. This disease usually causes thinned turf areas and/or thinned rings that can be full, half, or quarter circles, with various diameters. Turfgrass under drought stress or routinely irrigated with high salinity water is prone to infestation. Management of this disease on turfgrass is challenging. Some cultural practices can be beneficial, such as raising mowing height; and increasing fertility and using slow-release fertilizers to avoid nutrient deficiencies. This research evaluated 7 fungicide programs and a control, arranged in randomized complete blocks with 4 replicated plots per treatment on Bermuda grass at a golf course in Hawaii. Each plot was 10 ft by 10 ft, with 2-ft buffer area between adjacent plots. Treatments were applied 14 days apart, for a total of 7 times. Data (all on 1-9 scale) on disease severity, turfgrass greenness, and overall turfgrass quality were measured by 3 people prior to treatment and after each fungicide application. Results indicated that active ingredient Azoxystrobin resulted in the best disease suppression and turfgrass quality improvement, and active ingredient Chlorothalonil + Acibenzolar-S-methyl performed the second best. It is recommended that fungicide programs should be used in conjunction with cultural practices to manage this turfgrass disease.