THE DISTRIBUTION AND RECOVERY OF AERIAL ULTRA‐LOW VOLUME SPRAYS FOR CONTROLLING NYMPHS OF THE AUSTRALIAN PLAGUE LOCUST, CHORTOICETES TERMINIFERA WALKER

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Abstract
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 [Chortoieetes terminifera (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 (< 1 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 μm) than with a 25c setting (ca 70 μm). 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. terminifera 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.