Submitted to: Subtropical Plant Science
Publication Type: Peer reviewed journal
Publication Acceptance Date: 12/1/2004
Publication Date: 12/31/2004
Citation: Showler, A.T., Scott Jr, A.W. 2004. Effects of insecticide residues on adult boll weevils and immatures developing inside fallen cotton fruit. Subtropical Plant Science. 56:33-38. Interpretive Summary: The contact and residual efficacy of commonly used insecticides for boll weevil control in the Lower Rio Grande Valley of Texas have not been compared, nor the effect of insecticide application to fallen infested cotton fruit (squares) on adult boll weevil emergence. Five insecticides were compared in small plots, insecticide residues on cotton leaves were analyzed for effects on adult boll weevils, and effects of the insecticide sprays on fallen squares were evaluated in the laboratory. None of the insecticides were superior to the others when residues were aged 1-4 days, and the insecticides failed to kill the boll weevils developing within treated squares or bolls (mature fruit). These results indicate that any of the currently available insecticides for boll weevil control alone will provide the same level of crop protection.
Technical Abstract: The chief control tactic for the boll weevil, Anthonomus grandis grandis Boheman, during the cotton growing season in the Lower Rio Grande Valley of Texas is application of insecticides when squares first begin to develop, and when a threshold of 10% of randomly examined squares have oviposition punctures, which usually occurs around cut-out. Trap-collected boll weevils were used to assess direct contact and residual effects of cyfluthrin, befenthrin, azinphosmethyl, methyl parathion, and oxamyl on adult mortality, and egg-punctured squares and bolls were sprayed to assess toxic effects on immature stages developing inside. Adults sprayed with the insecticides all died within 30 min. In a leaf residue assay, bifenthrin caused the fastest mortality on the day of application, but none of the insecticides were superior to the others when the residues were aged 1-4 days. The insecticides failed to cause mortality to the boll weevils developing within treated squares or bolls. The limitations of the insecticides are one reason for repetitive late-season spraying in the Lower Rio Grande Valley.