Status of Spray Penetration and Deposition in Dense Field Crop Canopies

Abstract

HighlightsCrop production practices, spray drift control, and sprayer productivity affect spray penetration into dense crop canopies.Question is raised whether airflows near foliar surfaces or within the canopy can assist spray penetration under windy conditions.Current structural descriptions of canopies do not accommodate droplet trajectories to improve spray application.New nozzle tip designs, sensors, and air-assisted spraying need tuning to improve spray penetration and deposition.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 restricts 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 pertain 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. Keywords: Air-assisted sprayer, Airflow, Boom sprayer, Canopy openness, Droplet trajectory, Foliar canopy, Foliar density, Row crops, Spray blockage, Spray coverage, Spray deposit, Spray nozzles.