Further Field experiments on the control of wheat bulb fly, Leptohylemyia coarctata (Fall.)

Summary

Field trials were conducted in certain eastern counties of England in the years 1957–1959 to assess chemical control methods applied at sowing time against wheat bulb fly, Leptohylemyia coarctata (Fall.). Combine-drilled treatments, using fillers of aluminium silicate, brick dust, granular clay, superphosphate or compound fertiliser, included aldrin at rates from 0·3 to 5·5 lb., dieldrin at 2 and 4 lb., and heptachlor at 2 lb. active ingredient per acre, respectively. Seed-dressing treatments applied with organo-mercury fungicide included 40 and 60 per cent. dieldrin and heptachlor, 40 per cent. aldrin, 60 per cent. Thiodan, 40 per cent. _γ BHC with and without organo-mercury, all applied at 2 oz. per bushel of seed; 60 per cent. dieldrin, heptachlor and Thiodan were also tested at double the intended rate of 5 oz. per bushel.

No form of chemical control was completely effective in suppressing damage but all gave some, and usually a great, improvement, particularly on late-sown or backward crops. Most of the insecticides tested gave closely comparable results. Seed dressings containing at least 40 per cent. heptachlor, dieldrin, aldrin or _γ BHC were slightly more effective than combine-drilled insecticidal treatments, with the added advantage of applying only relatively small amounts of persistent insecticides to the soil.

Slight symptoms of phytotoxicity were observed on two sites in 1958 following the use of _γ BHC and dieldrin seed dressings applied at the normal rate of 2 oz. per bushel and severe symptoms on two trials in 1959 to seed over-dressed with insecticide and organo-mercury; elsewhere the seed dressings employed appeared to have no adverse effect upon plant establishment.

Dieldrin, aidrin, heptachlor and Thiodan seed dressings behaved similarly in killing a high proportion of larvae within attacked shoots; _γ BHC reduced the number of larvae entering the plant, but those which did succeed in entering developed in an apparently normal manner.

On fields where drilling was delayed and the attack severe, the optimum rate of combine-drilled aldrin was probably between 1 and 2 lb. active ingredient per acre. No significant increase in yield was obtained at rates much higher than 2 lb. per acre. While fine-dust formulations gave effective results, the use of a granular fertiliser base improved the flow through the combine-drill and gave increased tillering with slightly higher yields. Heptachlor combine-drilled at 2 lb. active ingredient per acre was slightly superior to aldrin at the same rate.

No adverse effects were recorded when insecticidal seed dressings and combine-drilled aldrin were used together, and at high levels of infestation the double treatment gave increased yields, though insufficient to justify its use on fields having only moderate egg populations.