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Abstract: Diseases still take a toll of our mushroom crops and the measures used to control them still are a part of the cost of production to be reckoned with. Sometimes we forget what the total costs of disease are. To the obvious loss in yield, the diseased mushrooms we must discard or sell at a low price, and the amount spent on chemicals and labour of applying them, must be added the concealed costs often overlooked. Changes in growing methods to avoid disease, choice of poorer varieties because of possible resistance to disease which result in lowered yield or quality are examples of costs which must be taken into account. Among changes in method affecting yield adversely are such factors as lowering humidity, refraining from watering, and lowering the temperature thus lengthening the picking cycle and causing mushroom harvesting over weekends or when the demand is poorest. In the United States many growers are using what we consider an inferior, tan-coloured variety, in the belief that with it they avoid virus infection, or at least virus disease symptoms. It has poor appeal on the fresh market. Such factors together with actual loss of infected mushrooms and the labour of removing them, with application of chemicals, with pasteurization of compost and casing, steaming or treating spent trays, and with filtering of air make up a very substantial item in today's cost of production. It is not only the presence of diseases which is important but also the cost of their absence. The problem, therefore, is not simply can the diseases be controlled, but at what expense. We are of the opinion that there is not one disease of mushrooms now known that cannot be controlled nearly completely with the means at hand. What the future must bring is, therefore, easier and cheaper control measures. What we should seek is more knowledge of the pathogens that cause disease to find their vulnerability to measures easily and cheaply applied, safe from the standpoints of chemical residues, environmental contamination, and for the personnel involved. Better and safer measures must be found with emphasis more and more away from chemical applications and towards control by environmental manipulation without depressing the yield or quality of mushrooms.
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