Amounts of DDT and its breakdown products were determined in soil in an apple orchard in Herefordshire. Samples were taken for a number of years (1972–79) after use of the insecticide in the orchard had ceased in 1969. The results were compared with those obtained in an investigation of the same orchard in 1968. From 1968 to 1979, soil residues of pp′‐DDT, p′‐‐DDT and pp′‐‐TDE decreased gradually whereas those of pp′‐‐DDE increased, and there were linear relationships between log (concentration) and time. The calculated time for 50% decrease in concentration (Dt50) was 11.7 years for pp′‐‐DDT, 3.3 years for pp′‐‐TDE and 7.1 years for op′‐‐DDT; the time for doubling the concentration for pp′‐‐DDE was 9.1 years. Regression analysis on the two major components (pp′‐‐DDT+pp′‐‐DDE) indicated that the total amount (2.7 mg kg−1) was not decreasing with time. It was concluded that during a post‐spray era, the breakdown of pp′‐‐DDT to pp′‐‐DDE was a significant feature of the persistence of DDT, and that, in contrast to the findings of other workers who sampled when DDT was being used, there were no losses by volatilisation. There was an exponential decrease in the amount of DDT residues with increasing soil depth and approximately 90% was found in the top 10 cm of the undisturbed soil profile.

Benzimidazole and its 2-amino analogue were non-toxic to Lumbricus terrestris when administered orally. The fungicidal 2-substituted benzimidazoles (benomyl, carbendazim, fuberidazole and thiabendazole) and l-(benzimidazol-2-yl)-3-butylurea were highly and equally toxic. The equitoxicity of compounds with widely differing substituent groups suggests a common mode of action-the benzimidazole moiety being the active part of the molecule. It is likely that there is a common mode of action for benzimidazole analogues for both fungicidal activity and earthworm toxicity. There was no detectable effect on the cholinesterase levels of earthworms poisoned by benomyl. But it is confirmed that the cholinesterase inhibitory activity of benomyl in vitro is due to formation of butyl isocyanate.

No abstract

Total deposits and their distribution on bush and dwarf hedgerow apple trees, sprayed at the late dormant and full foliage stages with a copper fungicide by five different methods, were estimated by colorimetric determination of the acid‐extracted copper from all the tree parts, and for comparison purposes were converted to equivalent volumes retained. The bush trees were sprayed by hand lance (4500 litresha‐1), by automatic nozzle mast sprayer (2250 litres ha−1), by conventional air‐blast sprayer at medium volume (1125 litres ha−1) and low volume (560 litres ha−1), and by hand‐directed ultra‐low‐volume (ULVH) fan‐assisted spinning‐disc sprayer (6 litres ha−1). The hedgerow trees were sprayed by conventional air‐blast sprayer at low volume (560 litres ha−1) and by an experimental tractor‐mounted ultra‐low‐volume air‐blast sprayer (45 litres ha−1). At the late dormant stage, the bush trees retained only 9–22 % of the total spray applied by all methods, except that those sprayed by the hand‐directed ULVH sprayer retained 57%. At the full foliage stage, when most of the spray was deposited on the leaves, retention for all methods of application was 22–37%. The hedgerow trees at late dormancy retained 6% of the spray applied in low volume and 10% of that by tractor‐mounted ultra‐low‐volume methods, but at full foliage, retention was 25 and 63 %, respectively. On both types of tree the proportions of the spray deposited on the tree components were related to the surface areas of those components.

Earthworm populations in apple orchard plots sprayed with benomyl and thiophanate‐methyl were greatly reduced. Lumbricus terrestris, a surface‐feeding species, was not found in the treated plots. Captive worms would not feed on leaf material with spray deposits of benomyl, MBC and thiophanate‐methyl at 1.75 μg/cm2, and feeding was significantly reduced when deposits were 0.87 μg/cm2. There was 100 % kill of worms in pots of soil within 14 days following a benomyl drench at the rate of 7.75 kg/ha, and a 60 % kill following a drench at the rate of 1.55 kg/ha. Worms immersed for 1 min in benomyl suspensions of 0.05 or 0.5 % died within 27 and 13 days respectively; those immersed in lower concentrations would not feed for 2 weeks but eventually did so. It is suggested that the lethal effects of benomyl may be due to anti‐cholinesterase activity of the carbamate moiety of the molecule.