Three formulations of malathion, each with 1 to 4 different doses, were aerially applied to cotton fields near Carlsbad, New Mexico for evaluation against boll weevil. An extensive bioassay using laboratory reared weevils and feeding and oviposition field damage estimates were used to assess the activity level of the different treatments compared to untreated weevils and plots. Mortality data resulting from all treatments for residue ages of 0, 2, 4, 6, 8, 10, and 12 days are shown. Feeding and oviposition damage data is shown for all treatments at 3, 7 and 14 days after application.

No differences in activity were demonstrated between the Cheminova and Griffin formulations at the program high dose of 0.93 lb AI/acre (12 fl oz/acre). Standard doses of both formulations lost activity between 4 and 6 days after treatments. Lower than traditional doses of Fyfanon ULV showed excellent activity equal to the high dose for at least 2 days after treatment.

All 3 doses of encapsulated malathion demonstrated activity equal to the standard dose for 2 days. Four day old residues of the high dose of encapsulated malathion, 0.77 lb AI/acre, showed a significant increase in performance over the equivalent standard dose, 80% vs. 47% respectively. Six through 12 days old residues of the high dose of encapsulated malathion continued to perform statistically better than the equivalent Fyfanon ULV dose. Numerically, 12 day old residues of encapsulated malathion in increasing dose rank order, produced mortalities, 1.5, 4.5 and 10 times greater than the 0.77 lb AI/acre Fyfanon standard dose. The increase in mortality among the 3 doses of encapsulated malathion suggests a 12 fl oz equivalent dose may produce 75% to 80% mortality. This level would be very similar to what the traditional dose showed after 4 days in this study. This possibility is extremely exciting because if such a level of activity is confirmed for that period of time, a doubling of the current interval between applications of malathion may be possible in the future. The data strongly suggests that an encapsulated dose equivalent to the current 12 fl oz Fyfanon treatment may demonstrate acceptable activity for ca. 2 weeks. Such improvement in treatment effectiveness could reduce overall pesticide load and application costs for boll weevil.