Persistence and effectiveness of thionazin against potato aphids on three soils in Southern England

Degradation curves were determined for thionazin applied to the soil in potato plots at three sites. Thionazin persisted longer in an acid, sandy soil than in an alkaline, clay soil, and residues were detected in the sandy soil a year after application. Results of residue analyses were confirmed by determining the kills of aphids ( Myzus persicae Sulz.) ‘sleeved’ on to potato plants. Natural infestation by potato aphids was effectively decreased only on plots treated with thionazin at 40 Ib/acre (44.84 kg/ha) on the acid sandy soil.