Velvet Shank, Flammulina velutipes and Chondrostereum purpureum on Horse Chestnut

In January I wrote about my first sighting of Velvet Shank, Flammulina velutipes, on a beech log in Grapes Hill Community Garden. Then a few days ago I found more Velvet Shanks growing on a Horse Chestnut on The Avenues in Norwich. They were so perfect I couldn’t bring myself to pick and eat them, preferring to leave them for other passers by to look at.

The Velvet Shanks were accompanied by a pretty purple bracket fungus, which I eventually identified as Chondrostereum purpureum.

It took me a while to identify the fungus, as it isn’t in most of my fungi books and Roger Phillips’ book ‘Mushrooms and Other Fungi of Great Britain and Europe’ shows some rather old specimens, not very like the ones I’d found. However his website (Roger’s Mushrooms) has some pictures submitted by members of the website, which look much more like my specimen. There are some more good pictures on the Arbtalk website, which also reveals that the fungus’ hosts include Beech, Birch, Cherry – and Horse Chestnut. The fungus is also called ‘Violet Crust’ and ‘Silver Leaf’.

The University of British Columbia (UBC) Botanic Garden website has a lovely picture of Chondrostereum purpureum. The accompanying article provides lots more information.

Chondrostereum purpureum isn’t edible. It causes Silver Leaf in fruit trees – plums in particular, but also apples, cherries and apricots. It has a wide distribution across the world. Leaves on infected branches have a silvery sheen and the affected branch will eventually die. Fungal spores infect new trees via wounds. The New Zealand Horticulture and Food Research Institute has a useful fact sheet on the disease on its website.

Velvet Shank, Flammulina velutipes and Chondrostereum purpureum on Horse Chestnut

For the organic grower, the best way to deal with Silver Leaf is to avoid pruning susceptible trees (in particular stone fruit such as such as plums) during the winter or on damp, cool days when there are likely to be more spores in the air. The New Zealand Horticulture and Food Research Institute has a useful pruning guide here.

Chondrostereum purpureum is being trialled in British Columbia for the control of aspen regrowth in forests (reference), as it infects broadleaves but not conifers. However, the article on the UBC Botanic Garden website notes that “given how easily fungi spread, one wonders if this could have deleterious effects on the British Columbia orchard industries, even with assurances that this ‘mycoherbicide is restricted to the target vegetation’ “. Indeed… this comment is especially relevant given our recent experience of aggressive fungal diseases such as Ash Dieback (Chalara fraxinea).