ABSTRACT
SoyOil 937® (93.7% soybean oil and 6.3% emulsifiers; Coastal Chemical Corp., Greenville, NC) at rates of 0, 0.7, 1.4, 2.8, and 5.6 l/ha was evaluated for adjuvant effects on physical spray characteristics of chlorothalonil. The rates corresponded to 0, 0.5, 1, 2, and 4% of the spray volume (140 l/ha). SoyOil 937 was tested with chlorothalonil and iprodione for control of early leafspot (Cercospora arachidicola) and Sclerotinia blight (Sclerotinia minor), respectively. Chlorothalonil (Bravo 720®) with various adjuvant concentrations was applied with D213 nozzles and 345 kPa pressure for control of early leafspot. Iprodione (Rovral 50W®) with adjuvant at 1% of the spray volume (335 l/ha) was applied with 8008LP nozzles and 165 kPa pressure. The addition of adjuvant at various rates to Bravo 720 did not alter spray volume, but the contact angle of spray droplets decreased as adjuvant levels increased. These results suggested an improvement in wettability of leaf surface. The frequency polygon for deposits of spray droplets approached a Gaussian distribution with a mean diameter of 255.4 μm. As the level of SoyOil 937 was increased, the distribution curve shifted toward a larger size in droplets. Leafspot incidence in field trials exhibited a quadratic polynomial curve with increasing levels of adjuvant up to 2% of spray volume in sprays of chlorothalonil. SoyOil 937 at rates of 0.5 and 1% of spray volume significantly improved leafspot control with chlorothalonil at 1.26 kg/ha, and was significantly better than chlorothalonil alone or at reduced rates with any level of adjuvant. The disease control efficacy of full and reduced rates of chlorothalonil was reduced significantly (p = 0.05) with adjuvant at 4% of spray volume. The performance of iprodione for control of Sclerotinia blight of peanut was not affected significantly by the use of SoyOil 937.
