PERSISTENCE OF AZADIRACHTIN-A AND AZADIRACHTIN-B IN SOIL - EFFECTS OFTEMPERATURE AND MICROBIAL ACTIVITY

The persistence of two insecticidally active compounds from the neem t ree, azadirachtin A and B, was determined at two different temperature s (15 and 25 degrees C) in the laboratory after application of the com mercial neem insecticide, Margosan-O, to a sandy loam soil. The influe nce of microbial activity on degradation was also examined by comparin g autoclaved and non-autoclaved soils also at 15 and 25 degrees C. Tem perature influenced degradation rates. The DT50 (time required for 50% disappearance of the initial concentration) for azadirachtin A was 43 .9 and 19.8 d for non-autoclaved soil kept at 15 and 25 degrees C, res pectively. The DT50 for azadirachtin B was 59.2 and 20.8 d for non-aut oclaved soil kept at 15 and 25 degrees C, respectively. Microbial acti vity was also responsible for faster degradation because DT50's for au toclaved soil were much longer than for non-autoclaved soils. DT50's f or azadirachtin A in autoclaved soil were 91.2 (15 degrees C) and 31.5 d (25 degrees C). DT50's for azadirachtin B in autoclaved soil were 1 15.5 (15 degrees C) and 42.3 d (25 degrees C). Two degradation product s of azadirachtin were detected, but were not identified. Higher level s of the two degradation products were detected in nonautoclaved soil.