Nozzle and Carrier Application Effects on Control of Soybean Leaf Spot Diseases

H. Mark Hanna, Iowa State University
Alison E. Robertson, Iowa State University
W. Mark Carlton, Iowa State University
Robert E. Wolf, Kansas State University

This is an article from Applied Engineering in Agriculture 25 (2009): 5, doi:10.13031/2013.25424. Posted with permission.


Increased soybean foliar disease potential has heightened grower interest in fungicide application techniques. Application field trials comparing application rate [187 vs. 112 L/ha (20 vs. 12 gal/acre)], nozzle style (twin‐orifice; single‐orifice) and spray quality (fine vs. medium and coarse spray quality), and application technique (with and without air‐assist) along with an unsprayed check were done at two locations over two years. Fungicide deposition (coverage and droplet size) and disease severity in the bottom, middle, and top parts of the plant canopy, and soybean yield were measured. Fungicide deposition coverage reduced from the top (8%‐18%) to the middle (4%‐8%) to the bottom (1%‐4%) of the canopy. Coverage was less affected by application treatment, however in wider rows [76‐cm (30‐in.)] coverage increased with the high‐rate and air‐assist treatments when spray quality was near the border between fine and medium. Conversely, in narrow rows [38‐cm (15‐in.)], least coverage was obtained with fine droplets produced by hollow‐cone tips on an air‐assisted sprayer. Size of droplets deposited generally followed predictions suggested by spray quality. Few disease severity differences were observed. Yield was unaffected by treatments sprayed during late reproductive stages (late R3 – R5) of the soybean plant.