Hormiactis cap spotting

Hormiactis sp. is an uncommon fungus that causes a cap spotting disease of mushrooms. It's normally a soil saprophyte but is pathogenic on mushrooms.

The spoilage it causes through cap spotting can render mushrooms unsaleable.

Overseas reports suggest that the fungus causes infrequent, localised disease on mushroom farms. It was recorded for the first time in Australia on a commercial mushroom farm in 2007.


A side-by-side comparison of cap spotting in mushrooms. The mushroom that was injected with the fungus Hormiactis alba has developed mould spots at the injection sites, while the mushroom that was injected with water has no mould spots.

The symptoms caused by Hormiactis sp. are similar to those of cobweb disease (Dactylium dendroides), particularly the dense, white mycelial growth.

Infection can also cause deformities of the mushroom.

Spread and infection

Information about Hormiactis cap spotting is limited. But it's considered to behave in a similar way to cobweb disease (Dactylium dendroides). With cobweb disease, the spores are released and quickly spread throughout the crop though the air conditioning system.

Conditions for infection are enhanced when the cap remains wet for a few hours.

Controlling the infection

You'll most likely get control of Hormiactis cap spotting using an evaporating atmosphere. However, be mindful of not compromising proper growing conditions for the mushrooms.

Reporting an unusual plant pest or disease

Report any unusual plant pest or disease immediately using our online reporting system or by calling the Exotic Plant Pest Hotline on 1800 084 881. Early reporting increases the chance of effective control and eradication.

Please take multiple good quality photos of the pests or damage to include in your report where possible, as this is essential for rapid pest and disease diagnosis and response.

Your report will be responded to by an experienced staff member who may seek more information about the detection and explain next steps.

Report online


Cunningham JH, Ratnayake K, Salib S, Irvine G, Priest MJ, Shivas RG (2008) First record of Hormiactis cap spot of mushrooms in Australia. Australasian Plant Disease Notes 3:19-20.

T.R Fermor (1979) Hormiactis alba, an uncommon fungal pathogen of the cultivated mushroom Agaricus bisporus. Glasshouse Crops Research Institute Annual Report, University of Warwick UK. pp. 191-193.

Page last updated: 05 Feb 2021