With the high cost of pesticide applications in terms of product cost, fuel and labor, as well as environmental impact, it is important to get as much benefit from fungicide sprays as possible. There are several things to consider in improving fungicide spray efficacy and efficiency.

Use an appropriate sprayer for the crop and calibrate your sprayer so you know you are applying the right amount of product per acre. This should be done at the beginning of the growing season. A good time to calibrate is in early spring. Check for worn disks and be sure that all nozzle tips have the same angle and capacity rating. Use the right kind of nozzles for the intended application. Nozzles that produce very fine droplets may lead to more drift and less deposition on the target. The use of wettable powder sprays enlarges nozzle openings, so calibration of each nozzle is essential. Use only clean water when calibrating sprayers. Calibration instructions can be found in E-154, 2012 Michigan Fruit Management Guide.

Adjust sprayer nozzles to aim at the intended target (e.g., fruit zone in grapes) – reduce speed and airflow to get more fungicide on the target and less drift. Remember any product that drifts away is lost for the purposes of disease control and may contaminate non-target areas and crops. A “patternator” can help you understand where most of the spray is ending up.

Apply the fungicide in a sufficient volume of water to obtain thorough coverage, but not lead to run-off as any fungicide that runs off the plant is lost and is more likely to contaminate ground water. Coverage is especially important for protectant fungicides. Spray volume should be increased as a crop canopy expands. For instance, for an airblast sprayer in grapes, it is recommended to start out with 30 gpa early in the season then increase to 50 gpa after bloom and maybe as high as 75 gpa at veraison. Spray every row. With an airblast sprayer, insufficient product is deposited on the second and third rows to get good disease control.

Check the pH of the spray solution, especially when using alkaline well water. While most fungicides are stable over a range of pH values, some fungicides (e.g., Captan, Dithane, Rovral) can degrade under alkaline conditions. For example, the half-life of Captan is 32 hours at pH 5, eight hours at pH 7, and 10 minutes at pH 8. The half-life of Dithane is 32 hours at pH 5, 17 hours at pH 7, and 34 hours at pH 9. (Insecticides in general are more sensitive to pH than fungicides.) For a list of pesticides and their sensitivity to pH, see the 2012 Michigan Fruit Management Guide, pages 59-60. The pH can be adjusted with an acidifying or buffering agent. Avoid letting the spray sit overnight in the spray tank. Fungicides should, whenever possible, be mixed and sprayed as soon after mixing as possible.