Does Spray Coverage Influence Fungicide Efficacy Against Dollar Spot?

Abstract

Chlorothalonil and myclobutanil were applied separately to creeping bentgrass using two sets of nozzles: two low‐drift nozzles that provided incomplete coverage [Teejet Turbo Turfjet nozzle (1/4TTJ04‐VS) and the Raindrop RA‐4 nozzle (35654‐2)], and two nozzles that provided nearly complete coverage [XR Teejet flat fan nozzle (XR11004‐VS) and the Teejet Air Induction nozzle (AI1004‐VS)], as assessed using water‐sensitive paper. Spray volume and pressure were equivalent with all nozzles. For both fungicides tested, in 48% of our assessment dates over four trials, the complete‐coverage nozzles controlled dollar spot better ( P < 0.1) than one or both nozzles that provided incomplete coverage. We saw no instance when nozzles providing incomplete coverage controlled dollar spot better than nozzles providing complete coverage. These results support the hypothesis that achieving complete spray coverage with fungicide provides more consistent control of dollar spot than incomplete spray coverage.