Volume 17 Part 1 Article 29: Microbial Degradation of Prochloraz in Mushroom Casing

Volume 17 Part 1 Article 29
Year 2008
Title: Microbial Degradation of Prochloraz in Mushroom Casing
Authors: H. Grogan, G. Papadopoulos, G.D. Bending and M. Wood


Prochloraz (active ingredient (a.i.) in Sporgon 50WP, BASF plc) is the main fungicide used in many countries to control dry bubble disease (Verticillium fungicola) in Agaricus bisporus mushroom crops. There is evidence to suggest that the concentration of prochloraz a.i. in mushroom casing can decline significantly during the life of a crop to less than 20% of what has been applied. Experiments were conducted to compare the persistence of prochloraz in mushroom casing under both laboratory and farm conditions. Rapid loss of a.i. occurred under farm conditions with ED50 values of 30 and 11 days being recorded compared with ED50 values of 85 and 48 under laboratory conditions. Agaricus bisporus had no effect on the rate of loss of prochloraz from mushroom casing. Experiments were conducted to identify possible sources of prochloraz degrading micro-organisms. Respirometer units were set up containing a culture medium with prochloraz as the sole carbon source as well as 14C radio-labelled prochloraz. Various samples were tested including fresh casing, peat, sugar-beet lime, prochloraz-treated and prochloraz-untreated third-flush casing, and residual liquid and sediment from inside a fungicide spray-tank. Microbial degradation of prochloraz was quantified by the evolution of 14CO2, which is the final breakdown product of 14C prochloraz. After 42 days incubation, significant prochloraz mineralisation was recorded for the fungicide spray-tank liquid (9.2%) and prochloraztreated third-flush casing (3.3%), while all other samples showed no significant prochloraz mineralisation and were similar to the control. Further work is required to identify if enhanced prochloraz degradation is a widespread phenomenon associated with residual liquid and sediment in fungicide spray tanks.

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