Dose-mortality and rainfastness of ULV malathion/cottonseed oil formulations for the boll weevil

摘要

Relationships were established between boll weevil mortality and malathion residues measured on cotton leaf disks before and after applying 2.5 mm of artificial rainfall. Four ratios of malathion to cottonseed oil (1;0, 2:1. 1:1. and 1:2) were applied to the leaf disks using a spinning disk sprayer. Bioassays of 24 and 48 hour mortality of boll weevils placed on leaf disks in petri dishes here compared to chemical assays of malathion on the disks. No significant differences in either 24 or 48 hour mortality acre found between the formulations. Data were pooled to obtain LD50 and LD90 estimates of 1.02 arid 2.25 mug malathion her cm(2) of leaf surface, respectively, at 24 hours of exposure arid 0.86 and 1.71 mug malathion per cm(2) of leaf surface, respectively, at 48 hours. The artificial rainfall washed most (66-88%) of the malathion residue froth leaf surfaces for all four ratios of malathion to cottonseed oil: correspondingly, post-rain mortality was reduced by 48-95%. These data should help boll weevil eradication managers to make decisions about reapplying malathion to fields subjected to rainfall between scheduled applications.