Whichever species of locust is considered, control strategy has always been limited by control technology. Early crop protection measures were confined to mechanical means. The development of synthetic insecticides and progress in application technology improved the efficacy of crop protection. Coupled with improved understanding of the biology and population dynamics of the major locust species, they also enabled strategic control in the form of plague and upsurge prevention.

Baiting and dusting constituted simple but inefficient methods of pesticide application, but it was the development of ultra low volume (ULV) spraying that allowed man to interfere with the progression of locust plague cycles. The technology for ULV spraying has developed from simple early devices such as the exhaust nozzle sprayer to safer and more efficient sprayers equipped with rotary atomisers for hand-held, vehicle-mounted and aerial spraying use.

Global positioning system (GPS) technology is a powerful new tool in locust control. The spatial accuracy and navigational guidance it provides simplify some of the most difficult tasks such as refinding targets and flying accurately spaced spray passes when no ground marker party is available. The technology also provides greater accountability in that the details of spraying operations can be recorded for later analysis.

Despite these improvements in knowledge and technology, locusts still pose major problems due to their mobility, the remoteness and inaccessibility of their habitats and the inconsistent commitment to maintaining monitoring and control capacity for a sporadic and infrequent pest. Upsurges and plagues have occurred in recent years and are likely to continue to do so in the future, albeit with diminishing frequency and severity.

Spray distribution in an apple tree canopy using an adapted knapsack mistblower fitted with a spinning disc, with the provision of an induced electrostatic charge on the droplets was studied.

Droplets were sampled using uvitex fluorescent tracer on Kromekote cards positioned in different areas of the canopy.

Droplets were highest on the outer surface and decreased sharply into the canopy. Uncharged spray droplets gave the poorer deposition with better distribution, but by adding an electrostatic charge, droplet deposition was significantly improved in the outer parts of the canopy. An average of 3 ml/tree of spray liquid was used in all applications. The larger variety (Red Victoria) required about 50% more spray liquid, but distribution was still lower than that achieved by the smaller Keswick variety.