Droplet Dynamics and Initial Field Tests for Microencapsulated Pesticide Formulations Applied at Ultra Low Volume Using Rotary Atomisers for Control of Locusts and Grasshoppers

The physical properties and field efficacy of microencapsulated acridicides (ME) were investigated to determine their suitability for application at Ultra Low Volume (ULV) rates in Sahelian conditions. Microcapsules were not damaged during application using Micronair AU7000 rotary atomisers. Drop size was dependent upon microcapsule size, smaller microcapsules tending to form dense aggregates within large droplets. The aggregation effect was counteracted by larger microcapsule sizes and by dilution of the concentrated formulation. There was a tendency for microcapsules to land dry at increasing distances from the point of application and at high temperatures and low humidities. In the field in Mali (W. Africa) diluted ME formulations were found to be suitable for ULV application by Berthoud C8 hand-held sprayers, vehicle-mounted Micronair AU7000 pest control kits and helicopter-mounted Beecomist rotary atomisers. ME formulations of fenitrothion, chlorpyriphos and diazinon all suppressed grasshopper populations in annual grassland and were as effective as fenitrothion applied at the standard ULV rate. The spatially heterogeneous and shifting nature of the grasshopper populations prevented the relative efficacy or persistence of the different products to be quantified and the potential for reduced environmental impact could not be tested.