Submitted to: Southwestern Entomologist
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 10/20/2001
Publication Date: 3/1/2002
Citation: Showler, A., Sappington, T.W., Foster, R.N., Reuter, K.C., Roland, T.J., El-Lissy, O.A. 2002. Aerially applied standard rate malathion against reduced rates of malathion+ cottonseed oil for boll weevil control. Southwestern Entomologist. 27(1):45-58. Interpretive Summary: The efficacy of malathion at lower than standard doses in cottonseed oil caused mortalities that were not statistically different among boll weevils exposed to differently aged residues during the first consecutive five days after spraying cotton fields. In general, the various rates of malathion did not result in differences in selected nontarget arthropod populations.
Technical Abstract: This study was conducted to determine whether reduced rates of malathion in cottonseed oil are as effective at causing boll weevil mortality as the current standard rate of ultra-low volume (ULV) malathion alone. In a field cage residue study, 693 g a.i. malathion + 553.5 g cottonseed oil per ha and 867 g a.i. malathion + 415 g cottonseed oil per ha caused a rate of boll weevil mortality over a five-day sampling period that was not significantly different than that caused by 1,040 g a.i. malathion per ha. In the field cage assay, mortality declined below 36% in all of the malathion treatments on the third day after application. The Petri dish assay showed that the malathion treatments had a measurable effect on boll weevil mortality for three days, and that daily % mortalities induced by the reduced malathion + cottonseed oil treatments were not statistically different than those induced by the standard rate. However, the magnitude of differences in mortality between 2 and 4 d after treatment suggest that residual activity of the reduced rates in oil may not be as great as the standard during this period. Nontarget arthropod groups, particularly lacewings (Chrysopidae and Hemerobiidae: Neuroptera) and Collops (Coleoptera: Melyridae) were reduced by all of the malathion treatments. In general, differential effects among the malathion treatments on nontarget arthropods were not observed.