Field trials were conducted to determine the effect of a number of factors on the distribution and recovery of ULV spray droplets, emitted from a light aircraft equipped with Micronair rotary cage atomisers for the control of Australian plague locust nymphs [Chortoicetes terminijera (Walker)]. Spray deposits were sampled with small oil-sensitive papers attached to pasture vegetation, and were analysed with a Quantimet 720 Image Analyser for droplet number and volume densities.Results indicated that volume recovery was 6 times higher in a strong (3-5 m/s) than in a light ( < I m/s) wind, and about 3 times higher with a 50" Micronair blade angle and thus a relatively coarse droplet spectrum (volume median diameter ca 120 pm) than with a 25' setting (ca 70 pm). Aircraft flying height (either 3 or 10 m) had little influence on average recovery, though the greater altitude gave a slightly more uniform spray distribution.Subsequent trials applying fenitrothion 128% w/v at 0.3 L/ha against C . terminijera nymphal infestations confirmed the effectiveness of spraying in a strong wind using the 50' blade setting; nearly 100% mortality was recorded and treated areas were cleared of nymphal bands in 2 d. Control was unsatisfactory in the light wind trial, despite a higher applied dosage of 0.38 L/ha.

As a preliminary basis to work on a method of chemical control of Australian plague locust nymphs, the influences of wind speed, emission height and droplet size on deposits of small insecticide droplets applied by a light aircraft equipped with Micronair rotary atomizers were investigated in a number of single-swathe trials. Deposits were sampled with small sensitive papers attached to the vegetation. The volume-median diameter of recovered droplets varied from 50 �m to 80 �m depending on the rotational speed of the atomizers. Results indicated that a strong wind (> 3 m s-1) would give good recovery of these small droplets, relatively uniform coverage and large swathe; but excessive drift could result if spray droplets were very small (60 �m) or if the emission height was too large (> 10 m).