Observations on the effect of soil type, treatment intensity, insecticide formulation, temperature and moisture on the adaptation and subsequent activity of biological agents associated with carbofuran degradation in soil

A sand, a sandy loam, a clay loam, and an organic (muck) soil all developed anti‐carbofuran activity within 28 days of an initial treatment. This activity was demonstrated by the rapid disappearance of the insecticide from the soils on retreatment. In all except the muck, homogeneous initial treatments of 10 and 1 ppm caused activity to develop while treatments of 0.1 and 0.01 ppm did not. Muck soil developed activity when treated at 100 and 10 ppm. Activity did not develop in the sandy loam at 1.3 and 4.5% moisture, but did at 5 higher moisture levels tested (9 to 36%). Likewise clay loam did not become active within 28 days when held at 20% moisture but did at 30, 40 and 50%. The effect of treatment intensity, formulation and temperature on activity development was examined only for the sandy loam. Activity developed on treatment with both granular and flowable formulations. Activity did not develop within 28 days at 3°C, but did at 15 and 28°C. Activated sandy loam maintained its activity when held at 6.8 and 4.5% moisture but not at 2.3 or 1.3%. It also exhibited only a slight reduction in activity when held at 15 and 3°C compared to 28°C. The intensity of the anti‐carbofuran activity was not dependent on the number of treatments given the soil (1–9), the treatment level (10 or 100 ppm) or the time elapsed since the last treatment (1–29 wk), but cross‐activity towards cloethocarb and oxamyl was affected. The intensity of the anti‐carbofuran activity developed by carbofuran pretreatment of sandy loam collected from the same field location at different times and the cross‐activity developed to carbaryl, cloethocarb and oxamyl varied.