Deposit characteristics and toxicity of fipronil formulations for tobacco budworm (Lepidoptera : Noctuidae) control on cotton

Three water-dispersible fipronil formulations have been tested for toxicity against second instar tobacco budworm, Heliothis virescens (F.). Topically , EC is the most potent of the three assays followed by WG and SC. However, pick-up assays on parafilm did not show significant differences in toxicit y between formulations. Droplet spread and deposit morphology of the formul ations were studied on cotton. Although the initial droplet spread was obse rved to be highest for EC, the final dried deposits of formulations were no t significantly different from each other. The deposit patterns of all thre e formulations on cotton are different. For EC, the formulation/AI is assoc iated with an annulus (outer ring) whereas the WG and SC are particulate in appearance and dispersed across the deposit. From the rain-washing studies on cotton, SEM photographs indicate that SC has greater retention than EC or WG. (C) 1999 Elsevier Science Ltd. All rights reserved.