Influence of temperature on solvent-pesticide interaction effects towards fungi

The effect of temperature on interactions between combinations of the solvent acetone and the fungicide captan was determined using the fungi Pythium uhimum, Sclerotinia homeocarpa, and Pestalotia sp. Seven concentrations of acetone, ranging from 0.1 to 3.0% (v/v), were interacted with four concentrations of captan, ranging from 1.0 to 10.0 ppm (mg L^?1 ). This procedure was repeated at 15, 20, 25, and 30 °C using potato dextrose agar at pH 5.5. Acetone and captan interacted synergistically towards P. ultimum and S. homeocarpa, and antagonistically towards Pestalotia sp., regardless of the temperature. The exact temperature response was dependent upon both the captan level and culture used. As the temperature increased from 15 to 30 °C, the toxicity of captan decreased by up to 40% with P. ultimum, and from < 10 to 20 with S. homeocarpa and Pestalotia sp. With only a few exceptions, the magnitude of interactions observed generally decreased as the temperature was increased from 15 to 30 °C. This was most pronounced with P. ultimum. Generally, the lowest interaction magnitudes were recorded at 20 °C for P. ultimum, 20 to 25 °C for S. homeocarpa, and 30 °C for Pestalotia sp. The greatest interaction magnitudes were usually obtained at 15 or 30 °C with P. ultimum, 15 °C with S. homeocarpa, and 25 °C with Pestalotia sp.