Herbicide spray deposition in wheat stubble as affected by nozzle type and application direction

Tall wheat (Triticum aestivum L.) stubble can enhance soil water conservation during the fallow-period by trapping snow and decreasing evaporation. However, standing wheat stubble can intercept herbicide spray droplets before they reach their intended targets. This experiment aimed to evaluate the effects of three wheat stubble heights (> 70 cm, 35 cm, and no-stubble), four nozzle types (XR, TTJ, AIXR, and TTI), and three application directions (angular (45°), perpendicular (90°), and parallel (0°) to the wheat row) on a spray deposition of glyphosate and a dicamba tank mixture. The ranking of droplet size from smallest to largest based on volume median diameter (VMD) was XR, TTJ, AIXR, and TTI. Wheat stubble greater than 70 cm decreased spray deposition 37%, while 35 cm stubble caused a 23% decrease. Sprayer application directions and nozzle type had significant interaction on spray deposition. Perpendicular application direction decreased spray deposition relative to the angular application direction for TTJ and TTI. Parallel application direction had lower spray deposition than angular application direction for TTJ and XR. Similarly, relatively-high-spray deposition (∼75%) was provided by angular application direction regardless of the nozzle type. Applicators should consider traveling in an angular direction to the wheat rows for improved droplet deposition across spray nozzle types.