MUSHROOM PESTS AND THEIR CONTROL ^5 



IXSECTICIDAL DUSTS 



There are a number of insecticidal dust mixtures on the market 

 that are used for mushroom fly control. A dust composed of 60 per- 

 cent of pyrethrum, with 40 percent of finely ground diatomaceous 

 earth or clay as a carrier, has been found satisfactory. The com- 

 mercially prepared dusts vary in composition, but are usually based 

 on this pyrethrum-carrier mixture, sometimes with other substances 

 added. It is desirable to get as fine a dust as possible so that it will 

 remain suspended in the air for a long time, and it is also well to 

 get as light-colored a dust as possible, since darker dusts sometimes 

 settle upon the mushrooms and render them unsightly, thus decreasing 

 their market value. 



The house should be watched carefully, and as soon as a few 

 flies appear it should be treated with the dust at the rate of 2 or 

 3 ounces per 1,000 cubic feet of air space. The majority of the 

 growers dust two or three times a week. Before dusting, the tem- 

 perature of the house should be allowed to reach 60° F. or more, 

 then the dust should be applied, and the house should be left closed 

 overnight. At any lower temperature the flies are less active and 

 the dust more inert. A good fan-type duster should be used and the 

 dust thoroughly distributed throughout the house. If a duster is 

 not available a good distribution of the dust may be obtained by 

 shaking the dust slowly out of a bag into the air blast from an 

 ordinary electric fan directed toward the ceiling of the house. 



FUMIG-ANTS 



Fumigation with calcium cyanide, at the rate of iy 2 to 2 ounces 

 per 1,000 cubic feet, has proved successful against adult flies if care- 

 fully used, but is said to retard the growth of mushrooms if the 

 fumigation is repeated more than four or five times. If this fumigant 

 is used, it is best to use it between "flushes." In preparation for 

 this fumigation the beds should be allowed to dry out for 2 days or 

 so, all salable mushrooms picked off, and the temperature allowed 

 to rise to at least 60° F. The house should then be fumigated and 

 left tightly closed for several hours. The aisles should be damp, 

 but not wet, when the calcium cyanide is spread upon them. 



MANURE FLIES 



At least three species of phorid flies (of the genus Megaselia) 

 have been reported as doing commercial damage in mushroom plant- 

 ings. These are M. albidihalteris Felt, M. agarici Lintner, and M . 

 iroquoiana Malloch. As in the case of the mushroom flies, these three 

 species of manure flies are so nearly alike in appearance and in their 

 biology that they may be regarded as one species when their control 

 is considered. They are frequently seen in immense numbers about 

 the compost heaps and on the exterior of the houses. The adult flies 

 (fig. 5) are black or blackish in color and usually slightly smaller 

 than the sciarid flies. They are much more compactly built, the legs 

 are stouter and not so long, and the head is rather small and the 

 thorax large, giving them a hump-backed appearance. They are 

 quite active, moving about constantly in a series of jerky runs. 



