Pests and Diseases Affecting Mushrooms
White mould (Bubbles): this is a fungal disease which covers the mushrooms with white mouldy growths; the gills are particularly vulnerable to infection, and a badly attacked mushroom may simply be a rounded mass, completely covered with the mould. In very bad attacks, whole clumps of young mushrooms can be enveloped in white mould and killed. Because white mould usually enters the beds in the casing, the best precaution is to use only peat or sterilized soil. Once an attack of white mould has occurred, remove and burn all infected mushrooms and stumps immediately. After the final crop, spray the containers and the inside of the building or greenhouse with a solution of formalin, or zineb.
White plaster mould: this is another fungal infection, which shows up on the surface of the beds as a pale powdery growth much like a top dressing of lime in appearance. It prevents the growth of the mushrooms and usually appears as a result of improperof the manure. It is favoured by alkaline conditions; the use of gypsum in the will generally prevent its appearance. If the beds have suffered from white plaster mould, disinfect the containers or building after the final crop.
Brown plaster mould: a relatively minor fungal infection, this appears on the surface of the bed first as a white fluffy patch. In a few days, the centre of the white patch will turn brown; eventually, the whole fungus turns brown and powdery. As with white plaster mould, improper composting is the main cause. Hygienic conditions and properly made compost will help to prevent its appearance.
Brown blotch: this bacterial infection makes the caps brown, sticky and inedible. Because it thrives in warm, moist still air, proper ventilation and moderate watering can avoid it.
Mushroom bed sclerotium: if you find branch-shaped, hardened growths in the casing soil, often with pinkish tips showing just above the soil surface, then your beds are infected with mushroom bed sclerotium. Pull them out of the soil and destroy them; you should still be able to harvest good crops.
Dry bubble: light brown spots and blotches appear on the mushroom cap, and later the mushrooms become distorted and the stalks split and peel. They become dry and leathery in time. Treat as for white mould; chlorinated water is also helpful.
Cobweb disease: a downy or fluffy mould appears on the compost surface and grows all over the mushrooms also, which then rot completely. Sometimes the mould has a pinkish tinge. Treat as for white mould.
Rose comb: the symptoms of this physiological disorder are deformed or cracked caps. Often gills are produced on top of the caps. Rose comb is caused by exposing the beds to fumes from oil stoves, or by applying mineral-based sprays.
Woodlice: these pests thrive in the humidity, darkness and decaying manure which are necessary for growing mushrooms. Once they enter the beds, either with the manure or else through cracks or holes in the shed, they will multiply rapidly. They eat holes in the developing buttons, and in severe infestations the entire crop can ruined. Gamma-HCH or pyrethrum applied to the bed are the best methods of control.
Slugs: slimy, silvery trails on the surface of the bed and ragged holes in the buttons indicate the presence of slugs. Hand pick if possible, at night when they feed, or trap them with proprietary slug baits as soon as they are seen, but put the bait near to the beds or boxes, rather than on them, as slug baits are poisonous to humans also.
Springtails: these tiny jumping insects often appear in great numbers and can do an enormous amount of damage. They attack the stalks, gills and outer edges of the caps, which then become slightly pitted. Once they have attacked the developing buttons, no further growth takes place, and the crops will be severely stunted. Compost which has heated up to the temperature recommended should not be troubled, but spraying or dusting the growing medium with gamma-HCH, pyrethrum or derris should control an infestation.
Sciarid flies: these tiny black gnats lay eggs on the surface of the compost and at the base of the mushroom stalks. The emerging tiny legless larvae, which are white with black heads, enter the base of the stalk and tunnel upwards; infected mushrooms decay. Treatment is the same as for springtails. High temperature composting in the first place will destroy larvae.
Mites: there are several species of mites which attack mushrooms, all of which eat internal holes in the stalks and caps. Unfortunately, mites have developed a resistance to most organochlorine-based insecticides, but derris or pyrethrum offer some measure of control. If the infestation is severe, the only completely effective method of control is to clear out all the beds, discard all the soil and manure, and disinfect the walls and floor of the shed with boiling water.
Phorid flies: these are similar to sciarid flies, and both insects do much the same damage. Phorid flies, however, are active mainly in the summer months, while sciarid flies occur all year round. The best preventive measure against phorid flies is to cover all ventilators, doors and windows with fine mesh screening. If an infestation does occur, spray or dust the beds with derris or pyrethrum.