Ultra-low-volume malathion is the most commonly used insecticide for the control of boll weevils in the United States. With millions of acres being treated each year, any efforts that extend the efficacy and thereby, reduces the amount of insecticide used can translate into significant cost savings to cotton producers. Various chemicals have been reported to extend the time that some viruses used for insect control are efficacious by functioning as ultraviolet protectants. Therefore, a study was conducted to evaluate three of these chemical protectants for their ability to decrease the rate of degradation of ULV malathion.

The chemicals that were tested as protectants were p-aminobenzoic acid (PABA), Congo Red, and Fluorescent Brightener 28. Each of the three protectants was added individually to ULV malathion, applied to cotton plants, and evaluated using leaf bioassays and chemical residue analyses. Each of the three compounds numerically increased the percent mortality in a leaf bioassay test at 0, 3, 6, and 10 days after treatment (DAT) compared to the ULV malathion only treatment. Boll weevil mortality in the protectant chemical treatments was significantly greater than the ULV malathion only treatment at 10 DAT. The treatment that contained Congo Red provided significantly greater mortality than the malathion only treatment at 3 DAT. All of the treatments that contained malathion were significantly higher from the untreated check on all sampling dates. Residue analyses were performed to determine malathion degradation rates. The Congo Red treatment only degraded by 10.8% by 6 DAT. All treatments degraded 59-75% at 10 DAT. The use of Congo Red in a field application of ULV malathion warrants further investigation.