Compost topdressing to suppress necrotic ringspot and improve the overall health of Kentucky bluegrass lawns

A study was conducted in northern Colorado to evaluate the effectiveness of two compost products on the improvement of turfgrass color and quality, necrotic ringspot (NRS) disease suppression, and thatch reduction. Two Kentucky bluegrass (Poa pratensis L.) home lawns with a history of NRS were chosen for the study. Treatments were applied twice during the 2018 growing season after all plots were aerated and consisted of (a) inoculated compost topdressing at a rate of 66 m³ ha^–1, (b) dairy manure compost topdressing at a rate of 66 m³ ha^–1, (c) urea fertilizer at 49 kg N ha^–1, and (d) a control (aeration only with no fertilizer or compost applied). Data were collected every 2 wk from May to October in 2018, and included the percentage of disease-affected turf, and turfgrass color and quality. Thatch depth was measured monthly. The inoculated and conventional compost plots had less disease than the control, and the inoculated compost showed significant disease suppression earlier than conventional compost. Season-long averages showed that the plots treated with either of the compost products had better color and turf quality than the control. When data were pooled over the course of the growing season, there were no significant differences between the two compost treatments with regard to NRS disease severity or quality. Thatch depth in plots that received inoculated compost was 17% less than in plots that received conventional compost and fertilizer. This study demonstrated that compost decreased NRS incidence and improved turf color and quality.