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ARS Home » Midwest Area » Wooster, Ohio » Application Technology Research » Research » Publications at this Location » Publication #316774
Title: Dynamics of water droplet impact and spread on soybean leaves

Author
item JIA, W - Jiangsu University
item Zhu, Heping

Submitted to: Transactions of the ASABE
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 7/2/2015
Publication Date: 8/11/2015
Publication URL: http://handle.nal.usda.gov/10113/61831
Citation: Jia, W., Zhu, H. 2015. Dynamics of water droplet impact and spread on soybean leaves. Transactions of the ASABE. 58(4):1009-1016.

Interpretive Summary: Soybeans are often sprayed with hydraulic nozzles to prevent attacks by insects and diseases. Questions arise as to whether pesticide droplets continue to stay on the plants and in what deposition patterns. This research examined dynamics of droplet impact, rebound, retention and spread on soybean leaf surfaces under controlled conditions with different droplet sizes, impact speeds, impact angles, and leaf surface inclinations. Test results demonstrated that water droplets did not rebound while large droplets slid on the leaf surfaces. This discovery suggested that effective spray application strategies for control of soybean insects and diseases should focus on improving precision and accuracy of droplet delivery with maximal droplet coverage on leaves and minimal use of spray rates. This suggestion will help spray applicators choose optimal spray rates with proper nozzles, operating pressures and other spray parameters to increase effectiveness of controlling soybean insects and diseases.

Technical Abstract: Soybeans are often sprayed to prevent significant yield loss from damage by insect pests and plant diseases. Understanding interactions of spray droplet reactions on soybean plant surfaces can lead to development of improved application strategies to enhance efficacy of pesticides. In this research, dynamics of impact and spread of water droplets of 185 to 693 µm at 1.85 to 6.4 m s-1 impact speeds and 28 to 75° impact angles on two soybean leaf surface orientations (horizontal and 30° inclination) were investigated with two high-speed digital video cameras and a mono-sized droplet generator under laboratory-controlled conditions. Within the test ranges of the variables, droplet rebounds were not observed after impact on leaf surfaces and droplets larger than 300 µm slid on the 30° inclined surface. Droplet spread ratios increased with droplet diameters and impact speeds but decreased with impact angles. Isoline distributions of droplet spread ratios were established to provide visual observations as a baseline for choosing optimal droplet diameter, impact speed and impact angle to maximize spray coverage areas. At similar impact speeds and angles, droplet spread ratios on inclined leaf surfaces were greater than those on horizontal surfaces. These discoveries elucidate that careful selection of controllable spray parameters to maximize droplet spread area and retention on soybean plants is essential for efficient soybean spray applications with minimal amounts of spray mixtures.