Droplet size and spray volume effects on insecticide deposit and mortalityof heliothine (Lepidoptera : Noctuidae) larvae in cotton

Effects of droplet size and volumetric application rate of tractor-applied lambda cyhalothrin (Karate Z 2.08 SC) on larval tobacco budworm, Heliciothi s vireseens (F.), mortality and insecticide deposition on and within the ca nopy. of mature cotton were explored by use of a laboratory bioassay incorp orating field-sprayed cotton and a field trial incorporating natural insect infestations. Insecticide was applied in all combinations of three distinc t droplet sizes and three volumetric application rates. Mortality of third- instar tobacco budworm occurring in leaf-disk bioassays was highly correlat ed with insecticide deposits (mug/leaf disk) at upper- and mideanopy levels . At the upper canopy level, mortality was negatively correlated with volum etric application rate and was not significantly correlated with droplet si ze. Deposit was negatively correlated with volumetric application rate at t he lower plant level and larval mortality decreased with increasing. drople t size. Results from this studs do not support the recommendations of high volumetric application rates; and although droplet size was less influentia l than volumetric application rate in deposit and insect mortality, the dat a indicate a significant tl end toward increased mideanopy larval mortality with smaller droplets.