CHARACTERISTICS OF AIR-ASSISTED AND DROP-NOZZLE SPRAYS IN COTTON
The effects of air-assisted, drop-nozzle, and over-the-top spray applications were characterized with a wide array of targets and chemicals in mature cotton foliage. Spray rates of 47 and 94 L/ha were applied at droplet volume median diameters (Dv.5) ranging from 114 to 192 µm. Increased spray rate predominantly increased deposition and chemical efficiency under most conditions. Sprays assisted with air (velocities up to 16 m/s) increased fluorescent tracer deposits on the canopy middle up to 92% of that from the canopy top, and resulted in a significant increase in bifenthrin on leaves and squares located within the canopy. Use of an upward-trajectory thiodicarb spray from drop-nozzle applications tended to control beet armyworm (Spodoptera exiqua [Hubner]) on the leaf underside more efficiently than the other application methods. Orienting the air-assisted sprayer air stream 30° back tended to increase deposits on the leaf underside. Use of air-assisted applications at 47 and 94 L/ha and an over-the-top application at 94 L/ha for a butifos and ethephon spray mixture provided the highest mean defoliation ratings that ranged from 68.1 to 78.4%.