Dollar Spot Severity as Influenced by Fungicide Mode of Activity and Spray Nozzle

Abstract

Dollar spot, caused by Sclerotinia homoeocarpa, is a severe disease of highly maintained turfgrass. Improving the efficacy of fungicides when applied in relatively low water volumes may be possible through the optimization of nozzle selection. The objectives of this research were to evaluate fungicide efficacy when delivered through five different nozzle types and to elucidate any potential interactions between fungicide mode of activity and nozzle type. Research was conducted at four locations in Pennsylvania and Connecticut in 2005. Chlorothalonil (contact mode of activity) and propiconazole (acropetal penetrant mode of activity) were applied alone or tank-mixed and delivered through five different nozzles. At all sites, no fungicide-by-nozzle interactions were observed, and dollar spot suppression was generally greatest when fungicides were tank-mixed. The TurfJet 1/4TTJ04 nozzle generally provided the poorest level of control when compared with all other nozzles (i.e., Air Induction AI11004, Turbo TeeJet TT11003, and XR TeeJet XR11003 or XR11004). Although the impact of nozzle type was not as pronounced under low to moderate disease pressure, nozzles that produce fine to coarse water droplets (i.e., Turbo TeeJet or XR TeeJet) or the Air Induction (AI) nozzle were associated with the best suppression under severe dollar spot pressure. Despite producing a very coarse droplet, the AI nozzle also facilitated excellent suppression of dollar spot under severe disease pressure. The use of AI-type nozzles may improve the efficacy of fungicides used to control foliar diseases while at the same time minimize the potential for drift to off-site targets.