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A small-scale laboratory method of determining the effect of wood preservatives on growth and cropping of the cultivated mushroom is outlined. Experiments with a number of well-known wood preservatives are described. According to these experiments wood treated with the following preservatives had no adverse effect on mycelial growth or on croppings: 5 % copper sulphate solution, green Cuprinol, 5 % Celcure solution, 2 % Triolith (Wolman salts) solution. On the other hand, wood treated with 2 % Chromel salt and coal-tar creosote reduced the vigour of growth of mushroom mycelium to a depth of 1/2 in. in compost that was in contact with it. Under these conditions, however, the mycelium was not killed nor was the cropping reduced even when the treated wood was only 1 1/2 in in. below the casing soil. As in all experiments the treated wood was covered with compost, the chance of vapours from the preservatives coming into contact with sporophores was very small, and the possibility of harmful effect in mushroom houses from such vapours should not be ignored.

The experiments indicate that full-scale trials in commercial mushroom houses could be undertaken with copper sulphate, green Cuprinol, Celcure and Triolith with negligible risk to the crop, but that it is advisable to carry out trials on a smaller scale with Chromel and coal-tar creosote of known composition to determine whether these preservatives have any adverse effect on cropping. Owing to the great range in composition shown by coal-tar creosote it is most important that the conclusions reached with the particular sample used in the above experiments should not be applied to creosotes in general.