Dry bubble (fungus spot) or Verticillium disease

Verticillium fungicola var.fungicola, V.fungicola var. aleophilum, V.psalliotae

Just like Mycogone, this mushroom fungus disease often occurs and causes considerable damage to the mushroom culture. Verticillium (or fungus spot) that has appeared on an early stage of mushroom development and wasn’t treated in any way, can colonize and practically destroy the whole yield.

The disease symptoms can be different; this depends on the time the infection occurred. Mushrooms that have diseased on their pinning stage, acquire a shape of a bulb (thick stipe and a very small cap) or develop into a shapeless mass of mushroom tissue. Unlike in the Mycogone disease, this mass doesn’t decay, and drops of liquid don’t appear on it, and there’s also no objectionable odor. Mushrooms diseased with Verticillium remain dry and have a leathery surface, which got the disease its name:»the dry bubble». The infection of mushrooms on a later stage causes a deformation of the stipe and an irregularity of the cap. For example, a so-called «hair lip» defect occurs when a mushroom infected from one side continues to grow with its healthy side and that causes it to crook, the outer side of its stipe breaks and curls back.

Mushroom fruit body, infected with Verticillium on the pinning stage

Mushrooms, infected with Verticillium on the stage of fruit body formation

Dry, leathery surface of a deformed mushroom infected with Verticillium

Mushroom fruit body, infected with Verticillium on the pinning stage

The deformation of mushrooms, when diseased with «fungus spot»

Distinctive Verticillium spots on the cap of a ripe mushroom
Distinctive Verticillium spots on the cap of a ripe mushroom.
When ripe mushrooms are diseased, grayish-brown spots of dead color appear on the cap. These spots grown into the mushroom tissue and when the humidity is high, a grayish mold appears on them. The dead color and intergrowing is what makes Verticillium spots different from the shiny, moist to the touch, brown spots of mushroom bacteriosis.

The source of Verticillium; and Mycogone also, is infected casing layer. Moreover, the spores of this fungus can be carried into the farm by flies, mites, personnel and also through unfiltered air.

The control measures of this disease are similar to the ones for wet rot (Mycogone). In particular:

• maintaining the hygiene on the farm;
• preventing the appearance of flies and mites on the farm;
• the preparation and storage of the casing mixture in a clean room. Mushroom wastes, outside soil, insects and rodents mustn’t get inside;
• Teaching the pickers and orderlies to identify the disease and treatment of the infected mushrooms. When sources of the disease appear, they must be strewed with salt and carefully removed, or watered with a formalin solution, strewed with lime and removed the following day;
• The removal of all infected mushrooms before harvesting or watering;
• Processing of the infected batches as soon as possible by steaming, or using a strong disinfectant;
• Immediate removal of all wastes from the farm.