Watering In Fungicides and Impacts On Dollar Spot Control.

Fungicide treatments are an important tool to combat many turfgrass diseases.  Dollar spot, caused by Sclerotinia homoeocarpa F.T. Bennett, is no exception, and typically requires the most fungicide applications per season on cool season turfgrass species.  With the advent of newer broad-spectrum and pre-mixed products, turfgrass managers are able to apply fewer fungicides to control a wide array of foliar and root diseases of turfgrass plants.  Watering in fungicides has been previously shown to increase effectiveness on root diseases like fairy ring and summer patch, but the impact of these applications on dollar spot control has not been reported.  In 2010, a 2 yr field trial was established on creeping bentgrass (Agrostis stolonifera L.) over two locations: Raleigh, NC and New Brunswick, NJ, to evaluate the effect of watering in fungicides on dollar spot disease.  The trial was arranged as a randomized complete block design with 4 replications having fungicide treatments (triadimefon, metconazole, azoxystrobin+propiconazole, pyraclostrobin+boscalid, fluoxastrobin+myclobutanil, trifloxystrobin+triadimefon, and triticonazole) that received both none and 5 mm of water immediately following each application.   All treatments were applied 2 times 8 weeks apart each year to observe residual control across the growing season.  During 2010, watering-in azoxystrobin+propiconazole reduced dollar spot control in both NC and NJ.  Metconazole and trifloxystobin+triadimefon also exhibited reduced dollar spot control when watered-in in NC while fluoxastrobin+myclobutanil and boscalid+pyraclostrobin control was reduced in NJ.  The mixture of boscalid+pyraclostrobin was not affected by watering-in throughout the season in NC and provided the best dollar spot control in both locations.  Based on these results, watering-in fungicides for root disease control can provide sufficient residual control of dollar spot disease during the growing season.