Influence of pyrethroid formulations and sprayer nozzle size on mortality of tobacco budworm larvae on cotton

Encapsulated formulations of two synthetic pyrethroids, Baythroid (cyfluthrin) and Scout (tralomethrin), were compared with respective nonencapsulated formulations for efficacy against tobacco budworm (TBW), Heliothis virescens (F.), larvae on greenhouse-grown cotton on a spray table using 650033 and 8002E flat fan nozzles. The volume median diameter (D sub(V0.5)) of spray droplets in the selected plumes of the two nozzles averaged 246.0 and 324.8 mu m, respectively; these values were significantly different. Using a spray volume of 18.7 L per ha, Baythroid was applied at 0.014 kg (AI)/ha and Scout was applied at 0.010 kg (AI)/ha. Encapsulation of Baythroid and Scout neither increased mortality of TBW larvae nor reduced fruit damage to cotton. Regardless of Baythroid formulations, smaller droplet sprays of the 650033 nozzle significantly increased mortality of TBW larvae compared to larger droplet sprays of the 8002E nozzle. However, the nozzle size of sprayers did not significantly influence TBW mortality for the Scout formulations.