Submitted to: Transactions of the ASAE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 9/26/2000
Publication Date: N/A
Citation: Interpretive Summary: Effective pest control is a critical part of the current production of abundant, high quality, nutritious food in the United States. Sprayers are used to apply many of the chemical or biological pest control agents. A high-quality spray system applies the minimum amount of pesticide uniformly to all parts of the spray target where pests are a problem. An important step in determining the quality of spray application is measuring deposit of spray droplets on leaf surfaces, or on other collectors that simulate leaf surfaces. Water- and oil-sensitive papers have been used to provide growers, spray operators and researchers with an image of droplet deposit patterns within crop canopies. Researchers also use imaging systems to estimate spray deposit based on spots on water-sensitive paper. A drawback of this method is that, during many spray applications, the water-sensitive paper in some parts of the canopy is so densely covered with water spots that the spots overlap and coverage cannot be measured accurately. One method to avoid the overlap problem would be to use a small quantity of crop-oil in the spray mixture. Then oil-sensitive paper could be used and the lower volume of oil in the spray would provide smaller spots that would be separated and measured. This is the first study to show that spray-deposits spots on oil-sensitive paper using dilute oil-mixture sprays are closely related to the spots on water-sensitive paper. Thus it is possible to use oil-sensitive paper to estimate spray coverage at all points in the plant canopy. Growers and researchers will be able to use this new tool to more precisely compare spray application systems. This should lead to more effective and efficient sprayer design and application methods.
Technical Abstract: Water- and oil-sensitive paper (WSP and OSP) were attached to tree leaves and to a tower bracket between trees. A petroleum spray oil was applied at a constant rate in four concentrations of spray oil in water (1:5.9, 1:10, 1:50, and 1:100) with 17 treatments. WSP and OSP were also sprayed in a laboratory with 8001 and 8004 flat fan nozzles. Spot size on oil- and water-sensitive paper at the same location for the same spray condition were compared by assuming the spots came from the same droplet size population. The spot sizes were sorted by size and divided into 25 classes by number. The mean size of each population was calculated for each size class and the ratio of water to oil spots was calculated. To reduce the effect of spot overlap, only sprayed samples with low populations (less than 20% coverage) of water and oil spots were used. Measured spot size ratios were compared to ratios calculated from droplet diameter ratios computed from volume mixtures and from known spread factors on water and oil sensitive paper. Water:oil spot size ratios predicted using known mixture ratios and spread factors agreed quite well with laboratory measured spot size ratios. However spot size ratios measured for field experiments did not agree with predicted values. This may have been due to larger water spots touching, or oil spots separating into several globules while the water portion of the spray droplet evaporates.