SUMMARY Six trials were done during three years (1966–69) in eastern England to study how known amounts of insecticidal seed dressings affect the growth of winter wheat and the severity of attack by wheat bulb fly larvae. In the first two years γ‐BHC dry dressing was applied to seeds previously treated with a liquid organomercury fungicide, but in the third year seeds were dressed with powders containing fungicide mixed with the insecticides γ‐BHC, chlorfenvinphos or ethion. Analysis using gas liquid chromatography showed that the ethion+ fungicide dressing stuck to the seeds much better than the chlorfenvinphos+fungicide dressing or either formulation of γ‐BHC. Some ethion, γ‐BHC and chlorfenvinphos later fell off the seeds, the exact amount depending on the method of drilling. Small amounts of insecticide, less than about 10μg/seed of γ‐BHC or less than about 15μg/seed of the organophosphorus compounds, were ineffective against wheat bulb fly. Increasing amounts of all three insecticides progressively decreased the percentage of damaged shoots and the percentage of plants with live larvae, but more of the organophosphorus insecticides, especially of ethion, was generally needed to give the same protection as γ‐BHC. No seed treatment damaged seedlings in trials on peaty loams or sandy clay loams, but seeds dressed with the standard amount of liquid organomercury fungicide and several different amounts of γ‐BHC dry dressing germinated poorly in the sandy loam soils.

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SUMMARY Under severe infestation pressure and delayed emergence following mid‐October drilling, only dieldrin seed dressing gave an acceptable control of wheat bulb fly, Leptohylemyia coarctata (Fall.). The control afforded by commercial seed dressings of BHC, carbopheno‐thion, chlorfenvinphos, ethion and the experimental compounds GS 13006 and pirimiphos‐ethyl, and by chlorfenvinphos granules was markedly inferior to that obtained with dieldrin seed dressing. In short‐row screening trials, bendiocarb, C 10015, C 18244, carbo‐furan, dialifor, ethoprop, iodofenphos, methiocarb, ‘Phosvel’, PPC‐3, propoxur and RD 21192 showed little promise. Phoxim and pirimiphos‐ethyl showed some promise but were not sufficiently active to warrant further study. Special seed dressing formulations of ‘Dursban’ did not overcome the inherent phytotoxicity of the compound to germinating wheat seed.

SUMMARY Seed dressings of organophosphorus and carbamate insecticides, at 0⋅1 per cent and 0⋅5 per cent active ingredient to weight of seed, were compared with heptachlor and ethion standards for control of wheat bulb fly during 1966–68. Short rows of treated seeds were sown in autumn on sites infested with wheat bulb fly eggs, and sample plants were examined in spring. The effective new materials, judged by the percentage of damaged shoots and the percentage of plants containing live larvae, were R 42211 (0,0‐diethyl 0‐(2‐diethylamino‐6‐methyl‐pyri‐midin‐4‐yl) phosphorothioate), B 77488 (0,0‐diethyl phosphorothioate 0‐ester with phenylglyoxylonitrile oxime), B 80833 (0‐methyl 0‐3,4‐dichlorophenyl methyl phosphonothionate), ‘Dursban’ (0,0‐diethyl O‐3,5,6‐trichloro‐2‐pyridyl phosphorothioate) and bromophos‐ethyl. However, both doses of ‘Dursban’ and bromophos‐ethyl. and the larger dose of B 80833 damaged young seedlings. There was only slight damage with the large dose of B 77488 and none with R 42211, so these two compounds were the most promising new materials tested.

SUMMARY Two trials were laid down with organochlorine seed dressings (gamma‐BHC, aldrin and dieldrin) and one spray application (aldrin) as standards. Various organophosphorus seed dressings and granules (applied broadcast before drilling or combine‐drilled) were also used. All treatments yielded significantly better than the controls in both trials except chlorfenvinphos, ‘Dursban’ and N2790, the first being significantly lower in the 1966–67 trial at the five per cent level and almost so in 1967–68. Parathion granules proved particularly effective, comparable to the best organochlorine, with the broadcast slightly better than the combine‐drilled treatment. Trichloronate and N2790 gave lower yields than parathion, but those from the latter were reduced by waterlogging. Phytotoxicity resulted in a poor establishment with the ‘Dursban’ formulation as did the liquid dressing of chlorfenvinphos in the 1967–68 trial, although this was not so apparent in the earlier trial with the 2 oz per bushel (2 g/kg) powder dressing. Ethion did not delay germination and, whilst it appeared to show activity during the autumn feeding phase, there was evidence that it, and chlorfenvinphos, afforded little protection later in the season.