Brown Cap Mushroom Virus: Symptoms

The symptoms of Brown Cap Mushroom Virus are complex and vary from crop to crop. Here’s what you need to look out for:

• An off-white or cream cap colour
• A coffee or deeper brown cap colour, which can appear on just a few mushrooms or on as much as 80% of a flush
• General poor quality of mushrooms, sometimes with premature opening

Even if there are only a few brown mushrooms in a crop, the virus could be present in the crop or the compost, so it’s important to maintain high standards of hygiene to prevent further spread. The virus may only occur in one flush (often the first).

It’s also worth noting that the browning might be visible on the bed before harvest, or it might not show until after the mushrooms have been picked and cold-stored.

Brown Cap Mushroom Virus is also known as virus AbV16. When this virus is present at low levels, the crop goes through a subtle colour change from pure white to off-white, which isn’t always detectable by eye. These mushrooms may still be of good quality. But if there’s a very high level of AbV16, you’ll see obvious brown discolouration on the caps.

Symptoms of Brown Cap Mushroom Virus: browning/"off-colour" white mushroom crop.