Pests & Diseases in Mushrooms

Verticillium

• Penn State College of Agricultural Sciences lists verticullium, or dry bubble disease, as the most common fungal disease affecting Agaricus bisporus mushrooms. Brown necrotic spots with fuzzy gray growth appear on the tops of mushroom caps. The disease often spreads up one side of the mushroom stem, splitting the infected side open. Bubble-like masses of mushroom tissue envelope infected mushrooms. Severely infected mushrooms weep amber drops of liquid. Infected mushrooms may not show any signs of infection until after harvesting, which leads to the spread of the fungus throughout the crop. The disease moves through air, water and physical contact. The cleaning of farm equipment with disinfectants and application of approved fungicides, such as Benlate, Bravo and Mertect, reduce the outbreaks and spread of verticillium through mushroom crops.

Green Mold

• Green mold infestations appear on soil, compost, equipment and mushrooms. Mold refers to any fungus that forms spores through asexual reproduction. Mushroom-based mold results from many different fungi, including trichoderma, penicillium and aspergillus. In the early stages, the mold is white. Mature, fruiting mold turns green and disfigures the mushroom. According to Alexander Tsarev, an agronomist specializing in commercial mushroom production, the potential mushroom loss depends on the type of mold and the degree of infection. Mushroom producers see few positive results when fighting mold infestations as the spores spread through wind, equipment, insects, animals and water. Prevention is key, beginning with strict cleaning guidelines for equipment and personnel.

Bacterial Blotch Disease

• Bacterial blotch disease occurs when mushrooms remain wet after watering. Pale-yellow lesions form on the mushroom, darkening to brown as the disease progresses. While superficial, the spotting often results in cracked caps as the mushroom grows. Penn State College of Agricultural Sciences recommends maintaining conditions to keep mushroom surfaces dry and free of condensation. Sodium hypochlorite added to irrigation systems helps control blotch, but only if the mushrooms do not remain wet for extended periods of time.

Mushroom Fly

• Oregon State University considers the sciarid fly the major insect pest of mushrooms. Numerous fly species damage mushrooms, including the cedid fly, house fly, phorid fly and stable fly. Fly larvae feed upon the mycelium, destroy developing mushrooms and tunnel into the stems and caps of maturing mushrooms. Adult flies transport mold spores, mites, nematodes and pathogens throughout mushroom crops. Management practices include cultural, biological and chemical controls. Proper sanitation, the sealing and screening of rooms and proper drainage techniques help reduce fly populations. Predatory nematodes and Bacillus thuringiensis israelensis applications may be affective against sciarid infestations, while predatory wasps help control house and stable flies. Registered pesticides for mushroom crops include permethrin, malathion and azadirachtin.

Nematodes

• Nematodes exist naturally in most agricultural soils. Parasitic nematodes affecting mushrooms feature needle-like mouth parts for the removal of mushroom cell contents. Saprophytic nematodes do not specifically attach mushrooms, but produce by-products that negatively affect the ability of mushrooms to grow. Nematode infestations result in the introduction of diseases to the mushroom crop. Mushrooms damaged by nematodes feature green mold and bacterial blotch infestations. Penn State College of Agricultural Sciences recommends killing nematodes during the over-cropping as the only means of control.