Nozzle and Carrier Application Effects on Control of Soybean Leaf Spot Diseases
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A two-site, two-year field application experiment investigated fungicide coverage in a fully-developed soybean canopy. Application treatments included “high-rate” (187 l/ha; 20 gal/acre) and “low-rate” (112 l/ha;12 gal/acre) with fine-droplet two-orifice tips, medium-droplet two-orifice tip at 187 l/ha (20 gal/acre), a coarse-droplet single-orifice “herbicide-style” tip at 168 l/ha (18 gal/ac), and an air-assisted spray treatment. Droplet coverage and size, and foliar disease severity in the lower, middle, and top parts of the plant canopy, and crop yield were measured.
Droplet size generally followed expected manufacturer specifications. Percentage area covered and drops/cm 2 were significantly less in lower parts of the plant canopy (1 – 8%) than in the canopy top (15 – 18%). Coverage was affected less by application treatment and differences observed in pooled data from all canopy locations were mixed. Although smaller droplets usually produced increased drops/cm 2 , percentage coverage did not always increase. In the second year coverage improved with medium droplets. Foliar disease pressure was light so that yield or disease severity was little affected by application method or as compared to a check area without application.