Interpreting results from co‐operative trials of insecticide treatments against cabbage root fly on summer cauliflowers

Abstract

SUMMARY The parameters used to assess the performances of soil surface and sub‐surface bands of chlorfenvinphos, chlormephos, diazinon, and fonofos granules against the cabbage root fly (Delia brassicae (Wiedemann)) in field trials at five sites in different parts of England in 1971 were: the root damage indices (RDIs) 4–5 weeks after transplanting and at harvest, the numbers of eggs, larvae and pupae per plant, the marketable yield and the percentage of plants with marketable curds. When the treatments were ranked for each parameter, the numbers of eggs or of larvae and pupae were no more informative than the RDIs 4–5 weeks after treatment or at harvest. Ranking also indicated that the percentages of plants yielding marketable curds, which could be determined without harvesting, revealed the relative effects of the treatments on yield as satisfactorily as the weights of the curds or the calculated numbers of crates per hectare. When the data for all parameters were summarised by ranking, the sub‐surface applications of chlormephos, chlorfenvinphos and fonofos were consistently the most effective treatments. Surface bands of chlormephos or diazinon granules were ineffective or, at some sites, enhanced root damage.