Leptohylemyia coarctata (Fall.) - Integrated Control and the Use of Economic Thresholds1

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.     

Some experiments with different formulations of organophosphorus insecticides as seed dressings to control wheat bulb fly (Leptohylemyia coarctata)

Experiments on the control of wheat bulb fly larvae by seed dressings compared four organophosphorus compounds in standard siliceous earth formulations with special formulations of the same compounds in polyvinyl acetate, polypropylene or wax. The special formulations allowed more insecticide to be placed on the seeds without affecting germination. Counting shoots damaged by wheat bulb fly larvae showed that: siliceous earth formulations of diazinon gave good control which was not improved by special formulations; control with siliceous earth formulations of dimethoate was poor and was improved only little by the special formulations; and control with siliceous earth formulations of parathion and dichlofenthion was moderate and was improved by special formulations, especially polyvinyl acetate and polypropylene. The results suggest that special formulations are of most value with compounds that are moderately effective but where the amount of insecticide in standard seed dressings cannot be increased without damaging the plants.     

Efficacy and phytotoxicity of multiple petroleum oil sprays on sweet orange (Citrus sinensis (L.)) and pummelo (C. grandis (L.)) in Southern China

The efficacy of pest control of three different oil formulations in multiple low-concentration spray programmes on sweet orange and pummelo were compared with unsprayed and normal farmer-treatments over three years. Phytotoxicity of sprays was assessed in terms of fruit and leafdrop, fruityield and external fruitquality. Trees sprayed with any type of oil had lower pest numbers than unsprayed trees. On sweet orange, the heaviest oil was better than the normal farm practice at controlling chaff scale on fruit and red mite and whitefly on leaves. On pummelo it provided the best control of red mite on leaves. All three oils were as effective as the normal farm practice in control of rust mite on sweet orange fruit and leaves and red mite, rust mite and red scale on pummelo fruit. On sweet orange trees there was no evidence of phytotoxicity, and the external quality of fruit generally improved over time. On pummelo trees, oil sprays were unable to improve the external fruitquality. The number of pummelo per tree was reduced in three of the oil spray schedules in 1995 and one in 1996, but the total weight of fruit harvested per tree was unaffected.