Chemical control of wheat bulb fly (Delia coarctata) attacking winter wheat in Eastern England, 1969–1981

Abstract

SUMMARYDry powder, liquid and microencapsulated formulations of organophosphate and synthetic pyrethroid insecticidal seed treatments were tested as possible alternatives to the standard organochlorine seed treatments for autumn‐sown wheat in mineral and organic soils heavily infested with wheat bulb fly eggs and (subsequently) larvae. Retention of insecticides on the seed coat varied from 40% to 120% of the target dose; it was usually good when microencapsulated formulations were used.Chlorfenvinphos, fonofos, isofenphos and triazophos, each applied at 2‐0 g a.i./kg seed, were phytotoxic, the symptoms varying from a slight delaying effect upon germination to an adverse effect upon grain yield. Chlorfenvinphos at 0–2 to 2‐0 g a.i./kg seed was consistently effective against wheat bulb fly larvae in both mineral and organic soils. Athidathion 0–8 g a.i./kg, carbophenothion 1–2 g a.i./kg, ethion 1–7 g a.i./kg and fonofos (microencapsulated formulations) at 1‐0 or 2‐0 g a.i./kg were also effective in mineral and organic soils. Of the synthetic pyrethroids tested as seed treatments, permethrin gave excellent results in mineral soils at 1‐0 g a.i./kg or in synergised formulations at 0–12 or 0–24 g a.i./kg but was disappointing in organic soils.In a single comparison of seed treatments applied to wheat sown early (14 October) and late (20 November), chlorfenvinphos was effective at both sowing dates whereas athidathion, ethion and pirimiphos‐ethyl gave better results in late‐sown wheat.A single trial compared deep with shallow sowing of treated seed. Most insecticides performed better on shallow‐sown wheat, but chlorfenvinphos was equally effective against the pest at both sowing depths.Most insecticides restricted the numbers of larvae entering host plants but had little or no subsequent effect upon larval survival within attacked shoots. Fonofos and isofenphos, and to a lesser extent chlorfenvinphos, seed treatments additionally killed many larvae within plant shoots.