Comparative effects of three insect growth regulator insecticides and a dipteran-active strain of Bacillus thuringiensis on cropping of the cultivated mushroom Agaricus bisporus

Three insect growth regulator insecticides and an entomopathogenic strain of Bacillus thuringiensis (GC327), products effective against the mushroom sciarid, Lycoriella auripila, were compared for their effect on mushroom cropping. Cyromazine and diflubenzuron were applied as a surface drench to mushroom compost before or after pasteurisation (at filling or spawning, respectively); admixed into casing material (at casing); or at a combination of these times. Hexaflumuron and GC327 were applied only at filling and casing, respectively. The presence of the target pest, L. auripila, had no effect on treatment trends, although it was accounted for in the analysis by use of a yield model. The trial was notable for the disparate effects that cyromazine and diflubenzuron casing treatments had on mushroom cropping. Cyromazine treatments that included application at casing resulted in increases in yield, compared to the untreated control whereas, with diflubenzuron, the opposite was true, with treatment at casing alone causing the greatest reduction overall (10%). GC327 applied at casing was also conspicuous for giving a 13% increase in yield. Treating the crop at casing with either cyromazine or GC327, therefore, resulted in a 15% or 24% increase in yield, respectively, compared to a similar treatment with diflubenzuron. Hexaflumuron applied at filling caused increases in yield compared to application of cyromazine at filling and cyromazine or diflubenzuron at spawning. There were also effects on crop timing. The addition of a cyromazine casing treatment normally caused the distinct flushes of mushrooms to be produced significantly earlier than the untreated control (up to 2.5 days), as did GC327. With diflubenzuron, the earlier flushes were only produced by those treatments that did not include a casing application. The combinations that included a casing treatment with diflubenzuron initially produced mushroom flushes earlier than the untreated control. They became either synchronous with the control or they were delayed. From the crop tolerance perspective, therefore, cyromazine and GC327 would be the sciarid control products of choice for a commercial mushroom grower.