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Abstract: In 1973 a client was experiencing significant reductions in yield in crops of Agaricus bisporus grown on his farms at Otford and Picton in New South Wales. I was asked to investigate the problem. The typical symptoms associated with these reductions were as follows:(1) The production of normal first flushes of mushrooms followed by a cessation of cropping after three or four flushes. (2) Large populations of mites were developing in these crops. These were later identified as Tyroglyphid mites. (3) In those beds which ceased cropping before the fifth flush large numbers of small pink mites were observed and no Agaricus mycelium remained on the straw or other compost components in these beds. These mites were the hypopus stage of the Tyroglyphid mites referred to in symptom 2. (4) Sciarid fly populations were also present in these crops at varying levels. Similar levels of fly populations in other crops on the same farm did not cause cropping to cease when the Tyroglyphid mites referred to in (3) were not present. The pink hypopus stage was often found riding on the bodies of the Sciarid flies in crops where both the Tyroglyphids and Sciarids occurred. When the above symptoms occurred the grower was experimenting with higher levels of nitrogen in his compost and this was causing problems particularly in phase 2 of composting when residual ammonia was often.difficult to remove and weed moulds resulted. The experiments reported in this paper were carried out to provide some information about the life history of the mites involved and to evaluate some chemicals for possible use as control agents.
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