Spray Treatment Effect on Droplet Penetration into Soybean Foliage Using a Wind Tunnel

Highlights Narrow-angled flat fan spot sprays and broadcast sprays were evaluated for spray penetration into soybean foliage in a wind tunnel. Row spacing affected the foliar spray penetration performance of all spray treatments. Selected spot sprays at narrow row spacings were statistically comparable to baseline broadcast sprays. Leaf area index was statistically negatively correlated with row spacing and served as a relative indicator of foliar density. ABSTRACT. Spot spray penetration into row crop dense foliage addressed pest targeting challenges and prudent protection of sensitive ecosystems. This study evaluated spray treatment penetration into live soybean foliage placed at three different row spacings in a wind tunnel operated at low wind speed. Narrow-angled pre-orifice spray treatments with flat fan sprays of 20°, 40°, and 60° were examined as single-nozzle spot spray treatments compared to two different 110° flat fan broadcast spray treatments applied with drift reduction and venturi nozzles. Results indicated that coverage and spot density of water sensitive papers (WSP) placed at foliar canopy heights of 10 and 25 cm above soil level (ASL) varied depending on the selected row spacing. While no single spray treatment always yielded a statistically significant advantage, equivalent performances were often observed between some narrow-angled spray treatments and broadcast spray treatments typically including the venturi-spray nozzle. Select narrow-angled nozzle treatments demonstrated statistically equivalent mean coverage and spot density compared to broadcast treatments at the 10 cm WSP height ASL. With careful selection, narrow-angle spot-spray treatments served as effective alternatives to broadcast spray treatments. Future studies should consider addressing the knowledge gap associated with the interaction of over-the-top sprays with insertion of droplets into foliar depths via predominant foliar routes and pathways typically associated with different row spacings. Keywords: Dense canopy, Leaf area index, Precision spraying, Spot spray, Spray technologies, Spray tips.