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Title: VISUAL AND IMAGE SYSTEM MEASUREMENT OF SPRAY DEPOSITS USING WATER-SENSITIVEPAPER

Author
item Fox, Robert
item Derksen, Richard
item Krause, Charles
item COOPER, J - OSU/OARDC
item OZKAN, H - OSU

Submitted to: Applied Engineering in Agriculture
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 6/7/2003
Publication Date: 6/24/2003
Citation: FOX, R.D., DERKSEN, R.C., KRAUSE, C.R., COOPER, J.A., OZKAN, H.E. VISUAL AND IMAGE SYSTEM MEASUREMENT OF SPRAY DEPOSITS USING WATER-SENSITIVEPAPER. APPLIED ENGINEERING IN AGRICULTURE. 2003. v. 19(5). p. 549-552.

Interpretive Summary: Spray coverage on target foliage is one of the most important measures of spraying success. Many different methods of accessing spray coverage have been used. One of the easiest to use and one that makes coverage immediately obvious, is water sensitive paper. This paper is coated with a bright yellow substance that turns blue when water droplets strike it. Common methods of measuring the coverage include visual rating systems by trained technicians and semi-automated, image analysis systems. In this brief note we discuss a set of water sensitive paper targets obtained from spraying nursery trees with air blast sprayers. Targets were analyzed with both visual ratings and an image system. A visual rating effectiveness score was assigned to each target and compared to percent-of-target covered and number of spots-per-unit-area. Spots-per-unit-area was counted both visually and with the imaging system. Spot overlap was found to give a much lower spot density for targets measured with the imaging system than when counted by technicians. The difference in measured spot density, measured by the two methods, increased as the number of spots on the targets increased. There was a great difference in target area covered by spots and the visual rating score of coverage. Some targets with a rating score of 5 (very good coverage) had less than 3% of the target covered with spots. These targets usually had many small droplets uniformly spread over their surface. These results are very important to growers, extension agents and other scientists who often use water sensitive paper to evaluate spray effectiveness.

Technical Abstract: Water-sensitive papers (WSP) were attached to leaves in nursery trees and sprayed with air-blast sprayers. Deposit patterns on the WSP were rated visually for coverage, from 1 (no spots) to 10 (completely blue). Visual counts of spot density (spots/cm2) were made for cards representing coverage ratings from 1 to 6. WSPs were analyzed with an imaging system; several spot size parameters, number of spots and area coverage percentage were measured. Visual ratings of 5, 6 and 7 had considerable variability in area coverage percentage. Sample WSPs with visual coverage ratings of 3, 5, 6 and 8 and minimum, median and maximum coverage percentages are presented. Visually measured spot density was greater than image-system measured spot density for all rating numbers, especially for higher spot densities. Spot density began to decrease at visual rating numbers greater than 6.