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Abstract: The use of sphagnum peat moss as a casing layer has become more and more expensive during the last five years in Australia. In 1974 when development work on GRAYPETE as a substitute was begun the price of imported Detorf (R) peat from Germany (the most popular brand at that time) had just risen from $8.00 per bale to $12.00 per bale. In 1980 a similar bale of peat could cost in excess of $20.00. As well as increasing in cost, the type of peat imported showed much greater variability in structure and pest incidence in 1980. In 1980 in Australia the need for a cheaper, more uniform casing material than sphagnum peat was very much greater than in 1974. We have seen the testing of a number of substitutes in recent years. Some of these include spent compost, N.S.W. sedge peat, composted sawdust (Anon. 1979), defibrated pine wood and bark, sugar cane bagasse, spent casing peat (Nair, 1980), basic slag, pine bark, poppy straw and other Australian sedge peats (Hanger and Bjarnason, 1978). The need for a substitute casing material was also receiving attention overseas. Paper mill by-product (Hayes et al., 1978), spent compost or waste paper products mixed with activated carbon (Stoller, 1979) and recycled casing (Atkins, 1979a) were some materials tested. GRAYPETE is a completely synthetic casing which is based on readily available and inexpensive recycled cellulosic wastes such as paper and cardboard to which are added a number of ingredients which improve the properties of the raw materials (subject of patent). Activated carbon is not one of these ingredients although similar raw materials had been chosen for testing as in Stoller's work (Atkins, 1979b). Promising results were obtained with some of the more advanced GRAYPETE formulations in laboratory experiments (Clancy, 1979). Mushrooms were slower to develop, however, when GRAYPETE was used. Differences in the structure of GRAYPETE from peat and the type of fungicide used were considered as possible causes. Two laboratory experiments and three experiments in commercial growing rooms to evaluate some possible modifications are reported in this paper.
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