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Abstract: It is now established practice in the United States to incorproate Diazinon°, 0, 0 diethyl 0-(2-isopropyl-6-methyl-4- pyrimidinyl) phosphorothioate, into the compost in an aqueous solution watered or "drenched" onto the compost at the time of "spawning" or inoculation. The United States Environmental Protection Agency has established a tolerance of 0.75 ppm Diazinon residual in mushroom tissue. Data from Cantelo and McDaniels(1) has shown that, at a level of 100 ppm Diazinon, as a function of the wet weight of the compost, no residues were detected at the 200 ppb level. Further data in the same paper claims that good control (94%) of the first emergence of sciarid flies could be obtained in small plot experiments. This data and that of Parsells(2) was the basis for a special use permit for incorporating Diazinon in compost. Diazinon, an organophosphate pesticide, is extremely reactive when in contact with soils of high organic content. Therefore, its half life as an insecticide is very short and the residual levels drop very rapidly(3). The mushroom grower must incorporate the pesticide at the time of spawning. This allows the pesticide to be mixed thoroughly throughout the compost and therefore give the maximum dispersal of insecticide in the compost. This fact will enhance efficacy; however, the fly larvae are most active approximately 10 days after spawning. At this time, the Diazinon is only present at low levels; therefore, its potential effectiveness is greatly reduced. Delayed release nutrients were introduced into the mushroom industry in 1975 as the commercial product Spawn MateTM. The delayed release nutrient is added at the time of spawning and employs the use of a microencapsulation process to delay the release of nutrients until later in the crop when the spawn is well developed and nutrient uptake can be maximized. This same technology was employed to develop a delayed release pesticide product containing Diazinon that would maintain the residual pesticide content at the original level of usage until the time of larval hatch. This technique resulted in higher rates of control of first generation sciarid flies than the traditional drench methods. In addition, the formulation contained a delayed release nutrient formulation with a twofold purpose: (a) to stimulate the development of spawn and thereby avoid the phytotoxic effect of spawn growth retardation associated with Diazinon usage; (b) to increase yield.
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