Droplet distribution densities of a pyrethroid insecticide within grass and maize canopies for the control of Spodoptera exempta larvae

Abstract A motorized knapsack mistblower fitted with a rotary cage atomizer was used to distribute a 2.4% ULV cypermethrin spray (VMD 55 μm; NMD 25 μm) within grass and maize canopies infested with Spodoptera exempta larvae in Kenya. Droplet densities deposited on paper targets placed at different distances downwind of the spray track at various heights and orientations were compared. Larval mortality was concurrently assessed at each sampling distance. A minimum of ∼9 droplets cm −2 was required to achieve 50% larval kill (LN 50 ), on the basis of which 95% mortality (LN 95 ) would require ∼28 droplets cm −2 . The biocidal area was ∼4.5mm 2 . Suitable track spacings to achieve LN 50 were estimated to be 25 and 45 m respectively for back-mounted and vehicle-mounted mistblowers in wind speeds ⩽ 2 m s −1 .