OFA Bulletin Jan/Feb 2010 : Page 3

January/February 2010 • Numb e r 9 1 9 Grower Research to Discover Strategies for Spray Delivery Success by Dr. Richard Derksen D elivering pesticides and other crop production materials to an ornamental canopy remains a challenge on many fronts. While different delivery options exist, understanding how best to use each device and recognizing its limitations will help growers achieve their production goals. Research conducted by USDA-ARS scientists at the Application Technology Research Unit (ATRU), Wooster, Ohio, is providing growers with a better understanding of the application process. In cooperation with the faculty at Ohio State University, several current and planned studies are evaluating the fate of spray within ornamental canopies as well as within plants themselves. Previous research studying the use of handgun sprayers has provided mixed results about how effectively sprays are deposited throughout a canopy. To help understand better the effect that spray volume and droplet size (fine, medium, and coarse) have on spray deposits, a greenhouse trial was established to treat a mature poinsettia canopy. Foliar samples and artificial targets were collected to assess the fate of spray in the canopy. Results for the fungicide residue on foliage and fluorescent tracer analysis from artificial targets were similar. For the same areas of the canopy, there were few differences in spray deposit between treatments. Fronts and upper areas of the canopy received more deposits than the backs and lower areas of the canopy. While not statistically different, the high volume (100 gpa) application produced the highest deposits on artificial targets across all droplet size ranges. There were no significant differences in overall spray deposit between the low (25 gpa) and medium (50 gpa) volume treatments. This study revealed that canopy position (front/back and upper/lower) and the operator’s ability to direct spray at each target plant had more influence over the amount of spray within the canopy than spray volume or droplet size. However, this study did not distinguish between deposits on the top and underside surfaces of leaves. The previous research clearly demonstrated that it is difficult to put spray material on the underside of leaves in the bottom part of the canopy and that the amount of spray deposited throughout a mature canopy is highly variable. A new greenhouse trial was conducted to help understand how to solve these problems. The underside leaf surface was selected as the intended target since this area is so difficult to treat (Figure 1). Targets were placed on leaves in the upper and lower elevations of mature poinsettia plants. A spray mix containing fluorescent tracer was applied over the test area by handgun (Dramm Hydra) and broadcast boom treatments. The handgun (Figure 2) was used to make applications at different volumes (50 and 100 gpa) and different O F A B u l l e t i n Figure 1. Artificial targets on underside leaf surface. Figure 2. USDA personnel treating poinsettias with Dramm Hydra handgun. pressures (135 and 520 psi). The two over-the-canopy broadcast treatments included a boom using twin-fan nozzles (Figure 3, page 4) and an air-assist treatment using a flat fan nozzle (Figure 4, page 4). Despite the relatively short distance between the upper and lower canopy sampling sites on the poinsettia plants in this study, significant differences in under-leaf spray deposits were noted by elevation for most treatments (Figure 5, page 4). Continued on page 4 3

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