Status of spray penetration and deposition in dense field crop canopies

Authors: WOMAC, ALVIN - University Of Tennessee; OZKAN, ERDAL - The Ohio State University; Zhu, Heping; KOCHENDORFER, JOHN - National Oceanic & Atmospheric Administration (NOAA); Jeon, Hongyoung

Submitted to: American Society of Agricultural and Biological Engineers
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 8/10/2022
Publication Date: 9/30/2022
Citation: Womac, A., Ozkan, E., Zhu, H., Kochendorfer, J., Jeon, H. 2022. Status of spray penetration and deposition in dense field crop canopies. American Society of Agricultural and Biological Engineers. 65(5):1107-1117. https://doi.org/10.13031/ja.15091.
DOI: https://doi.org/10.13031/ja.15091

Interpretive Summary: Extensive methodologies have been investigated and documented to improve spray deposition quality inside field crop canopies; however, there are no clear integrations of these methodologies to fundamentally address requirements for adequate spray penetration and targeting deposition when complicated interactions of local microclimate and airflow inside dense canopies are encountered. In this paper, representative publications were reviewed for improved techniques of spraying dense field crops to augment the current understanding of the interaction among the target foliage characteristics, spray practices, and the meteorological conditions. Comprehensive knowledge of relationships between spray deposition and canopy foliage density was instituted from numerous literatures that documented natural airflow within crop canopies, spray penetration into lower part of plants, and air assistance in droplet movement and deposition. The information from this study will provide extensive educational materials for spray applicators to efficiently apply pesticides, and will also provide guidelines for researchers to establish modern spray application practices and research directions.

Technical Abstract: The objective of this study was to review representative publications for improved knowledge of spraying dense field crop canopies to augment the current understanding of the interaction between target foliage characteristics, spray practices, and the environment. Emphasis was placed on measured deep-canopy spray deposits made by full-scale sprayers, and studies of airflow within and around crop canopies. Airflow could act as a spray droplet carrier and/or indicator of the internal canopy structure that restricted droplet penetration. High variation in natural airflows was noted in several studies. Crop canopy descriptions for spray studies were generally limited to overall canopy/row dimensions, descriptions of individual plant structures, leaf shapes, and leaf area index. Few studies evaluated the internal canopy “openness” with characteristic shape and size of internal volumes that would accommodate spray droplet trajectories. There have been significant increases in available spray tip designs with multiple orifices, discharge configurations, and droplet sizes that offered the applicator many choices. Advanced sprayer technologies ranging from nozzle control to sensor navigation are available, provided that suitable algorithms can be developed in a timely manner that pertains to a wide variety of spray and crop conditions. The air-assist technique provides a dynamic alternative to traditional over-the-top sprays for increasing spray penetration and deposit, advocating that the specifics of air discharge, spray droplet sizes, and canopy structure can be integrated. The complexity of the spraying process needs an extensive collaborative effort of many stakeholders to develop solutions for sprays to penetrate foliage that is subject to diseases and pests.