Fungal diseases in mushrooms: Cobweb disease

The primary symptom of Cobweb disease is circular patches of cottony white cobweb-like mycelium growing over casing soil and mushrooms. It can also cause yellowing, pink-tinged discolouration and irregular brown spotting (either on the bed or post-harvest).

When the Cobweb colony is well established on mushrooms and casing, it develops a powdery, granular surface due to the production of masses of dry spores. Sometimes, Cobweb colonies develop a pink tinge as they get older.

Cobweb mycelium grows at a rate of at least 1–2 cm per day and thrives in humid conditions. Within a few days of spreading, the disease produces masses of dry powdery spores. These are easily dislodged and spread.

Watering releases masses of spores into the air, where they can be rapidly distributed around the growing room via the air circulation system. They can also exit through open doors and exhaust vents, and attach to dust, debris and equipment around the farm.

This rapid spread shows why it is so important to identify and treat Cobweb disease quickly.

1. Clearly mark all the areas you are going to treat.
2. Dampen some strong, double thickness paper tissue and cover the affected area gently with a border of at least 5 cm. Make sure the edges are well sealed to stop the spores escaping.
3. If there are growing mushrooms beneath the paper, try to break the connection with the casing, to stop growth.
4. Check the areas regularly to make sure there has been no regrowth nearby.

Images are courtesy and copyright of INAGRO and Teagasc

Example of Cobweb Disease growing over brown mushrooms

© John Peeters

Yellow and pink discolouration on mushrooms caused by Cobweb Disease