Foliar spray banding characteristics
Foliar spray banding was explored as a means of reducing peticide use compared to broadcast applications. Barious geometric spray patterns and delivery angles of foliar spray bands were investigated to increase spray deposits in a crop row at a constant spray rate of 94 L/ha. Wind-free laboratory results indicated that a banded application using three 65° hollow-cone nozzles, with a laser-measured volume median diameter (VMD) of 110 μm, resulted in the highest (p = 0.05) upper canopy coverage of water-sensitive paper (WSP) of 37% compared to 31% for a broadcast, 80° flat-fan application (VMD = 152 μm). However, the fore-aft trajectory created by a twin-orifice nozzle (VMD = 135 μm) resulted in less upper canopy deposit and did not increase deposit in the lower canopy. No statistical differences were observed in lower canopy WSP coverage. Cumulative volume distributions (CVD) of deposit droplet spectra in the upper and lower canopy indicated that large droplets were deposited on WSP in the lower canopy. Field test results indicated that the broadcast, 80° flat-fan nozzle produced the numerically highest malathion residues of 7.5 ng/cm2 on leaf tops, but this was not statistically different (p = 0.05) from a banded 40° flat-fan nozzle application. Banded twin-orifice and three-nozzle hollow-cone treatments produced teh statistically lowest (p = 0.05) leaf-top residues of <3 ng/cm2. No significant (p = 0.05) differences were observed in leaf bottom residues and boll weevil mortality. In summary, downward-pointed sprays produced the greatest leaf-top residue levels under field conditions with a weak crosswind. Banded, narrow-angle (40°) flat-fan nozzles resulted in more deposit than a three-nozzle hollow-cone nozzle arrangement in the field. Thus, light wind conditions appeared to negate any advantages offered by multiple geometric spray patterns and delivery angles.