Leptohylemyia coarctata (Fall.) - Integrated control and the use of economic thresholds 1

Abstract Yields of crops attacked by wheat bulb fly can be predicted, but this cannot be done until much damage has occurred. In this situation the concept of economic thresholds is of limited use. It is much more important to be able to predict the likelihood of infestations as this enables the correct use to be made of prophylactic seed dressings. This and other approaches to integrated control are discussed

Effect of formulation on toxicity to plants and insects of some systemic insecticidal seed dressings

Abstract Wheat, mustard and sugar beet seeds were treated with dressings containing certain systemic insecticides and various stickers and fillers. Activated carbon, polyvinyl acetate emulsion and a chlorinated diphenyl resin lessened the toxicity of the insecticides to seedlings grown in sand. Polyethylene glycol ethers and polyvinyl alcohol solution also had some effect. Carbon and polyvinyl acetate prolonged the period of systemic action of ?Thimet? against the mustard beetle Phaedon cochleariae F. and the bird-cherry aphid Rhopalosiphum padi (L.). Mustard plants grown from seed treated with ?-BHC formulated with these materials were slow to attain their maximum insecticidal activity. These effects are attributed to the initial absorption of insecticide by the sticker or filler and its subsequent slow release. Formulations permitting the slow release of insecticides have a practical use because they can combine low phytotoxicity with a long persistence of systemic insecticidal activity

Wheat bulb fly, Leptohylemyia coarctata Fall., and its effect on the growth and yield of wheat

SUMMARY In two experiments done in successive years to compare the growth and yield of Cappelle wheat either protected from or exposed to attacks by larvae of wheat bulb fly, the plots were previously fallowed, but egg laying was prevented on half of each plot by using Polythene soil covers. In the first season wheat was sown at the end of October, November and December and in the second season in late October and in early January, when there were two sowings, one with and one without a spring application of herbicide. The infestation rate was 1·1-1·7 million eggs per acre, typical of a moderate attack. Larvae had little effect on the yield of October-sown wheat as the plants had two shoots each when first attacked and few were killed. On plots sown late, yield was decreased by up to 22%, as plants had only a single shoot when attacked and many were killed. The main effect of wheat bulb fly was to reduce the number of ear-bearing shoots by killing plants and restricting the production of new shoots. Surviving plants partially compensated by producing more ear-bearing shoots with heavier ears and slightly heavier seeds than normal. Killed plants were not distributed uniformly but were often in patches several feet across. Wheat on the attacked plots ripened more slowly and unevenly than on the unattacked plots. Weather affects the growth of the plants and activity of the larvae and thus partly determines percentage shoot survival

The uptake of phorate, a systemic insecticide, applied as a slurry to wheat and mustard seeds

SUMMARY The absorption by plants of wheat and mustard of a systemic organophosphorus insecticide (phorate), applied as a slurry seed dressing, was studied by caging the aphid Rhopalosiphum padi (L.) on the foliage of wheat, and the aphid Brevicoryne brassicae (L.) and the Chrysomelid beetle Phaedon cochleariae (F.) on white mustard, grown from phorate-treated seed. Wheat and mustard plants quickly lost their toxicity to insects when they were transplanted, suggesting that most of the insecticide from a slurry seed treatment passes into the soil and is picked up by the roots. That phorate or its derivatives occur in the soil was shown by tests of anticholinesterase activity. Insecticide can also pass into the seed of wheat and move to the growing embryo. Phorate becomes closely bound to the testa of mustard, but does not penetrate it to reach the cotyledons or other parts of the embryo. Mustard cotyledons can become contaminated by insecticide as they emerge through the soil. Young and old leaves of both wheat and mustard depend on continued absorption of insecticide from the soil to maintain their toxicity. No insecticide moves from old to young leaves. Old leaves lose their toxicity to insects more slowly than young ones. When treated seeds are sown close together, the overlapping zones of insecticide round each seed can increase strength and persistence of insecticidal effect. This happens more with dimethoate, which readily dissolves in water, than with phorate, which is almost insoluble. At normal sowing rates the zones of insecticide round each seed would rarely overlap. Roots of wheat and mustard from treated seed did not excrete insecticide, and the roots did not carry insecticide through the soil