Submitted to: National Cotton Council Beltwide Cotton Conference
Publication Type: Proceedings
Publication Acceptance Date: 1/8/2000
Publication Date: N/A
Interpretive Summary: Boll weevil eradication programs have continued to expand in the past few years resulting in millions of acres being treated with ultra-low-volume (ULV) spray applications of insecticide (malathion) to control boll weevils. Many researchers have shown that rates as low as 10 or 12 oz. of ULV malathion per acre can provide effective control of the boll weevil. Since any decrease in the rate of malathion used in eradication programs can translate into substantial savings for cotton producers, a study was conducted to compare the standard treatment of 12 oz. of ULV malathion per acre to a treatment containing 6 oz. of ULV malathion and 6 oz. of once- refined cottonseed oil. The cottonseed oil was added to the reduced rate of malathion treatment so that the same spray application parameters (nozzles, pressure, flowrate, etc.) would be used for both treatments. The efficacy of controlling boll weevils was evaluated for both treatments using a leaf bioassay test and by caging weevils on treated plants. The reduced rate of malathion treatments was inferior to the standard 12 oz. of malathion per acre treatment. However, rainfall events occurred throughout these tests and the preliminary results require further testing.
Technical Abstract: Efforts to reduce insecticide usage and increase cost savings to cotton producers have resulted in millions of acres treated each year with ultra- low-volume (ULV) malathion for boll weevil control. Many researchers have reported consistently lower effective rates of ULV malathion, with 12 oz. of ULV malathion per acre being the current standard rate. A study was conducted to compare this standard treatment with a treatment of 6 oz. of ULV malathion plus 6 oz. of cottonseed oil per acre. The cottonseed oil was added to the reduced rate of malathion so that the application parameters such as application rate, nozzles used, etc. would remain constant and not confound the results of the study. The efficacy of each treatment was measured by a leaf bioassay test conducted in the laboratory and by caging boll weevils on whole plants in the field. Evaluations were done at 0 and 2 days after treatment (DAT). Results indicate that 12 oz. of ULV malathion/acre was superior to the reduced rate treatment. The one exception was the 2 DAT measurement on the first sampling date for the leaf bioassay; however, it started to rain during the collection of the samples, which may have influenced the results. The cage study, which allowed the weevils to move freely about the treated plants, had lower mortality readings than the leaf bioassay tests.