Slow release pirimicarb granular formulations: Measurements of release rate under field conditions

Various granular formulations based on a non‐disintegrating granular carrier of the aphicide, pirimicarb, were tested for release rate under natural conditions by placing the granules in small bags made of a non‐woven fabric in various soils and analysing the contents at monthly periods. There was complete release from the control formulation within 1 month. The other formulations contained slow release additives. These slowed down the release rate but half of the active ingredient was still released in the first month from the formulation with the slowest release rate. It appears that if very slow rates of release are required than a different type of granule is needed. Laboratory release rates bear some relationship to field results justifying the use of laboratory tests as a method for selecting a short list of formulations for testing in the field.