Application of ultra-low-volume malathion by air-assisted ground sprayer for boll weevil (Coleoptera: Curculionidae) control

During 1994 and 1995, test of ultra-low-volume applications of insecticides conducted on cotton, Gossypium hirsutum L., at Stonealle, MS, evaluated the effectiveness of malathion applied with a new technology in ground application, the air-assisted ultra-low-volume ground sprayer. Two tests conducted in 1994 determined the effectiveness of ultralow-volume applications of malathion (91%) with and without cottonseed oil and established effective malathion rates against boil weevils, Anthonomus grandis grandis Boheman. An emulsifiable concentrate (EC) formulation of azinphosmethyl was used as a standard. In 1995, ultra-low-volume malathion (95%) was applied at 1.36 and 1.02 kg (AI)/ha plus cottonseed oil in a total volume of 1.17 liter/ha. These treatments were compared with a 1.12 kg (AI)/ha rate of an EC formulation of malathion applied with water in a total volume of 46.8 liter/ha. In the 1994 insecticide comparison test, ultra-low-volume malathion treatments resulted in 70% mortality throughout the 48-h test period whereas mortality from the azinphosmethyl standard steadily decreased from 71% at 4 h after treatment to 12% at 48 h after treatment. In the 1994 malathion rate test, 1.30 and 0.98 kg (AI)/ha produced mortalities comparable to those of azinphosmethyl at 0.28 kg (AI)/ha. In 1995, 48-h mortalities at 24 and 48 h after treatment were highest for the rate at 1.36 kg (AI)/ha (99 and 90%, respectively), followed by the rate at 1.02 kg (AI)/ha (78 and 54%, respectively), and lowest in the EC formulation treatment (28 and 21%, respectively). There were no differences in mortality at 72 h after treatment. The air-assisted ground sprayer permitted application of insecticides at considerably lower volumes than a conventional hydraulic ground sprayer and also permitted a reduction in the current rate of ultra-low-volume malathion required for effective boil weevil control.