Insecticide Reduction Through Precision Foliar Banding With Various Spray Nozzles and Droplet Sizes

The concept of precision foliar banding application was explored as a practical means of reducing insecticide use. Customfabricated 40-degree flat fan, standard hollow-cone, and twin-orifice nozzles applied over-the-row bands at 94 L ha-1, based on treated area in band, in field and controlled environment tests. Standard broadcast 80-degree hollow-cone and flat fan nozzles served as control treatments.

Field testing under 6 kmh-1 wind conditions produced WSP coverage, as determined by digital image analysis, of 38, 31, 30, 28, and 19 percent for banded 40-degree flat fan, broadcast 80-degree flat fan, banded twin orifice, broadcast twin orifice, and 3-nozzle banded hollow cone nozzles, respectively. The fan nozzles provided greater (p=0.05) coverage than twin-orifice and hollow cone nozzles. It was hypothesized that wind prevented small droplets from twin-orifice and hollow cone nozzles from settling onto the target. Malathion residue rankings from leaf tops were similar to WSP coverage rankings, though no statistical differences were found in residues from leaf bottoms and in boll weevil mortality.

Controlled-environment testing with no wind showed that coverage on WSP placed in the upper canopy ranged from 19 percent for a banded 40-degree nozzle to 37 percent for the 3- nozzle banded hollow cone nozzles. These were significantly different from the 30 and 31 percent coverage produced by broadcast twin orifice and flat fan nozzles, respectively. The increased coverage with the hollow cone nozzles of the tests was attributed to the lack of wind not affecting small droplets. Although no statistical differences (p=0.05) were determined for WSP coverage in the lower canopy, imagery analysis of WSP showed that large drops (VMD = 618 μm) penetrated the canopy, whereas small droplets (VMD = 224 μm) were deposited on WSP in the canopy top. Comparisons revealed that WSP generally overestimated the droplet spectra compared to a Malvern laser diffraction instrument.

Economic analysis showed that insecticide foliar banding reduced chemical input costs proportional to the ratio between bandwidth and row spacing. An insecticide-intensive cotton production system could realize annual insecticide savings ranging from $7.90 ha-1 for Delta-grown Bt cotton to $30.43 ha-1 for Coastal Plain-grown standard cotton. In conclusion, use of narrow-angle flat fan nozzle technology to apply foliar bands of insecticide to row crops provides a simple, cost effective solution to reduce insecticide use.