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



PLASTER-MOLD DISEASE 



The plaster-mold disease has been known for many years in France, 

 England, and Italy, where it .has been the cause of great losses. The 

 attention of the department was first called to it in 1920, when it 

 appeared in the beds of a grower in California. This grower traced 

 his trouble to spawn in which the fungus was introduced. This mold 

 has been known to North American growers for some years, but it 

 has never before attained the serious proportions which it has recently 

 assumed. It is unlike the bubbles or Mycogone disease in all respects, 

 as, for instance, time of appearance, method of injury, and appear- 

 ance both to the naked eye and under the microscope. It is not a 

 parasite on the mushroom, but runs through the manure, preventing 

 or delaying the development of the spawn. If the fungus is abun- 

 dant a loss of the entire crop may result. However, if the fungus is 

 present in a more limited amount, mushrooms will develop later, but 

 the crop will never be normal in quantity. 



The plaster-mold fungus appears on the surface and sides of the 

 beds as white patches which may be seen when the boards are raised. 

 At certain stages in its development the fungus may also be seen by 

 digging down into the beds, but it is generally dirty white or darker, 

 according to the age of growth. When mature the white patches 

 of the fungus are powdery. A microscopic examination shows the 

 white areas to consist of thousands of colorless oval spores borne in 

 chains. As the fungus matures, the chains break up and the spores 

 separate. The spores are light and easily carried by wind; thus the 

 disease is easily spread. Small insects, especially flies, may also 

 spread the disease and are an unusually important factor in its distri- 

 bution. As the fungus is present both in the manure and on the sur- 

 face of the beds, insects come in contact with it at different stages of 

 their development. Locating manure piles for refilling beds in close 

 proximity to mushroom houses is a very dangerous practice, because 

 the flies covered with spores gather around the doors and when they 

 are opened the flies come out in great numbers and light on the 

 nearest pile, shedding spores on the manure, which start a new 

 growth of the fungus. In this manner the manure is often well 

 infected with the fungus before it is taken into the house to make up 

 new beds. 



The study of control methods for this disease is being carried on, 

 but no satisfactory means has yet been found. The disease is very 

 difficult to control because the spores are so numerous and easily dis- 

 tributed by wind and insects. The danger of infecting new manure 

 not yet brought into the houses is therefore very great, and every 

 effort should be made to avoid introducing infection in that way. 



INSECT CONTAMINATION IN MUSHROOM HOUSES 



The presence in mushroom houses of the two diseases considered 

 above renders it even more than ordinarily necessary to control va- 

 rious insect pests which attack mushrooms. Every grower is 

 familiar with the small black mushroom flies which produce the 

 maggots in the caps, and with the losses which they are at times 

 capable of causing. He may not, however, appreciate their pos- 

 sibilities in the distribution of such diseases as plaster mold and 



