Chemical control of onion fly, Delia antiqua (Meig.)

Abstract

SUMMARYIn eight field plot trials in Cambridgeshire and Bedfordshire in 1977–79, insecticidal seed treatments and granules were tested against onion fly larvae. Carbophenothion, chlorfenvinphos, dieldrin, fonofos, iodo‐fenphos, permethrin and pirimiphos‐ethyl were tested as seed treatments in soil. Chlorpyrifos, dieldrin and pirimiphos‐ethyl were tested as seed treatments in peat blocks. Chlorfenvinphos and pirimiphosethyl were also tested as granules incorporated in soil and in peat blocks.Pirimiphos‐ethyl at 5 or 10 g a.i.†/kg seed and chlorfenvinphos, carbophenothion or fonofos each at 10 g a.i./kg seed gave good control of onion fly: all seed had been treated in the laboratory. Chlorpyrifos and pirimiphos‐ethyl seed treatments at 10 g a.i./kg seed were effective but severely phytotoxic to plants grown in peat blocks. Iodofenphos at 5 or 10 g a.i./kg seed was unsatisfactory when the seed was treated in the laboratory, but commercial treatment of seed gave adequate protection from attack. Permethrin at 2.5 g a.i./kg seed gave poor control and dieldrin at 30 g a.i./kg seed provided good control only where flies were not resistant. Granules of pirimiphos‐ethyl at 1.1 kg a.i./ha or chlorfenvinphos at 2.3 kg a.i./ha generally gave satisfactory control when incorporated in the top 2 cm soil at sowing, but the chlorfenvinphos treatment reduced seedling emergence. Chlorfenvinphos granules incorporated in peat blocks at 22.0 mg a.i./peat block (0.45 g a.i./kg peat) and pirimiphos‐ethyl granules at 2.5 mg a.i./peat block (0.05 g a.i./kg peat) gave only moderate control of onion fly attack, but pirimiphos‐ethyl granules at 5.0 or 10.0 mg a.i./peat block (0.1 or 0.2 g a.i./kg peat) were effective without apparent phytotoxicity. None of the seed treatments or granules entirely prevented egg laying by onion fly females. Following seed treatment, residues of chlorpyrifos, fonofos, iodofenphos and pirimiphos‐ethyl in harvested onions were <0.3 mg/kg.