8 CIRCULAR 2 7, U. S. DEPARTMENT OF AGRICULTURE 



the air of houses in the form of nicotine dust or evaporated from 

 commercial solutions or nicotine paper which can be purchased 

 from almost any seedsman or nursery firm. The commercial nico- 

 tine preparations vary in strength to such an extent that it is im- 

 practicable here to furnish detailed directions as to the dosage. It 

 is, therefore, suggested that directions on the commercial package be 

 followed in fumigating with this material. Nicotine will not in any 

 respect damage the mushroom crop or prevent the running of the 

 spawn. 



Free nicotine is preferable to nicotine sulphate for use in mush- 

 room houses, as it is rapidly volatilized and may be sprayed on the 

 beds. Nicotine-sulphate solutions, on the other hand, are only 

 slightly volatile and require the addition of an alkali to release the 

 free nicotine and render the solutions fully effective. The soap 

 ordinarily recommended for this purpose by the manufacturers is 

 injurious to the growth of mushrooms when sprayed on the beds, so 

 the use of air-slaked or hydrated lime at the rate of 1 pound to each 

 50 gallons of nicotine-sulphate solution is recommended as a 

 substitute. 



HTDKOCYANIC-ACID GAS 



Hydrocyanic-acid gas is used to some extent in mushroom houses 

 as a fumigant. In practice is may be applied at either of two differ- 

 ent times in the course of cropping. A number of growers fumigate 

 the house with calcium cyanide at the rate of 1 pound per 1,000 

 cubic feet at the time of maximum heat before spawning and after- 

 wards give it a thorough ventilation. The advantage of this method 

 is that at that time the insects ordinarily concealed in the compost of 

 the bed are driven therefrom by the heat generated by the manure, 

 which at times reaches 150° F. They are then likely to be well ex- 

 posed to the action of the fumigant, since they are congregated on 

 the outside of the beds where the temperature is lower. A single 

 fumigation applied at this time is particularly effective in destroy- 

 ing the majority of insects carried into the house in the compost or 

 breeding thereafter up to the time of fumigation. 



The practice of fumigating with light doses of calcium cyanide, 

 applied two or three times a week over a period of two weeks, has 

 also gained some headway with commercial growers. Some opera- 

 tors have recommended the use of 3 ounces of sodium or calcium 

 cyanide to each 1.000 cubic feet of space, applied preferably after 

 the gathering of the crop and while the atmosphere of the house is 

 relatively dry. In the event that houses containing growing mush- 

 rooms are fumigated, care should be taken that the fumigation is 

 conducted on a rising temperature, as otherwise the moisture pre- 

 cipitated upon the young caps may cause serious spotting and burn- 

 ing. The gas may be released in the evening and the house 

 thoroughly ventilated before sprinkling down the following morn- 

 ing. The tightness and construction of the house will have a bear- 

 ing on the dosage required, and the quantity mentioned above, i. e., 

 3 ounces to 1,000 cubic feet, should be considered as a maximum. 

 Growers have found, however, that the process of fumigating at 

 this rate is somewhat dangerous, as the margin of safety between 

 effective fumigation and damage to the crop is relatively narrow, 



