Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/8/2000
Publication Date: N/A
Interpretive Summary: Millions of acres of cotton are treated in the United States to control boll weevils using ultra-low-volume malathion. Studies have shown that malathion degrades rapidly in the field due to sunlight, temperature, and moisture. A study was conducted to try to extend the time that malathion is effective in the field by adding chemicals that protect malathion from sunlight or ultraviolet (UV) radiation. Three UV protectant chemical treatments with malathion were compared to a treatment with only malathion. The efficacy of the various treatments to control boll weevils was compared using a leaf bioassay test and residue analysis. One of the UV protectants tested (Congo Red) showed promising results and will be evaluated in a field study in the upcoming season. Any efforts that extend the time that malathion is effective in the field will result in fewer treatments being needed to control boll weevils. Fewer treatments will translate into cost savings for U.S. cotton producers and less material being released into th environment.
Technical Abstract: Ultra-low-volume malathion is the most commonly used insecticide for the control of boll weevils. Any efforts that extend the efficacy and 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. Studies were 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 percent by 6 DAT. All treatments degraded 59-75 percent at 10 DAT. The use of Congo Red in a field application of ULV malathion warrants further investigation.