Effects of Nozzle Type and Carrier Application on the Control of Leaf Spot Diseases of Soybean
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Midwestern soybean growers seek information on effective application of foliar fungicides that do not translocate throughout the plant. Field application treatments included using a two-orifice nozzle tip producing fine droplets at 187 l/ha (20 gal/ac) and 112 l/ha (12 gal/ac) and a single-orifice nozzle tip producing a coarse droplet size more typical of herbicide applications at 168 l/ha (18 gal/ac). In addition an air-assisted sprayer was used at one of the two sites of the trials. Measurements included droplet size, droplet coverage, and foliar disease severity in the top, middle, and lower parts of the plant canopy, and soybean yield.
Droplet size for application treatments generally followed expected manufacturer specifications. Percentage area covered and drops/cm 2 were not statistically different among application treatments except at top of the plant canopy at one site. Percentage area covered and drops/cm 2 were statistically greater at the top of the canopy (17 - 18% coverage) than at the middle or bottom (1 – 8% coverage) at both sites. Foliar disease pressure was light so that yield or disease severity was unaffected by application method or as compared to a check area without application.