| Field experiments were conducted from 2000--2002 to evaluate weed control and economic performance of a light-activated sprayer (LAS) in cotton. Herbicide treatments were applied with a broadcast sprayer, a conventional hooded sprayer (CS) or LAS. Treatments included prometryn at 1.34 kg ai/ha preemergence followed by (fb) cultivation as needed (ASN); glyphosate at 1.12 kg ai/ha applied postemergence over-the-top (POT) at the four-leaf growth stage of cotton fb glyphosate at 1.12 kg ai/ha applied with CS ASN; glyphosate at 1.12 kg ai/ha applied POT at the four-leaf stage fb glyphosate at 1.12 kg ai/ha applied with LAS ASN; and glyphosate at 1.12 kg ai/ha applied in a 36-cm band over the row at the four-leaf stage plus glyphosate at 1.12 kg ai/ha applied with LAS fb glyphosate at 1.12 kg ai/ha applied with LAS ASN. Weed control was evaluated 14 and 28 days after the last treatment was applied (DAT). Herbicide savings were calculated by measuring the amount of spray solution in the tank before and after treating each LAS-treated plot. Economic analysis included total specified expenses and fixed expenses (irrigation maintenance and hooded sprayer cost); and returns above total specified expenses, derived from the sale of cotton lint and seed. The light-activated sprayer generally controlled weeds similar to the conventional sprayer and better than cultivation, regardless of whether a band or broadcast application of glyphosate was made at the 4-leaf growth stage of cotton. The additional cost of LAS was offset by reductions in herbicide use; however, net returns were not increased when compared to a conventional sprayer. Additional research was conducted to investigate the potential for plant species differentiation by spectral reflectance. Reflectance was measured using sixteen wavelengths for two crops and four weed species at two growth stages. When small plants were measured, wavelengths 600, 630, 650, 670, 700, 1600, and 1700 nm revealed no similarities between species. At wavelengths 450, 470, 630, 650, and 670 nm, data revealed that reflectance of large cotton plants was different from every weed species evaluated. Wavelengths were identified that have potential for use in species differentiation by spectral reflectance measurements. |
