Last year we discovered patches of what looked like a pretty, felted pink mould on the underside of the leaves of our black hawthorn shrub (Crataegus douglasii). As this “mould” caught the sunshine, it glittered like crystals. After a while the fuzz turned brownish.
We had never seen it before, so I examined it under the microscope to try and figure out what it was. What I found was a tangle of plant cells with unusual shapes but no sign of any typical fungal features.
After searching unsuccessfully online for an answer, I finally packaged a specimen and sent it off to a plant pathologist, Joey Tanney, at the Pacific Forestry Canada office in Victoria.
Joey was quite curious about it as he suspected that it was not fungal, but rather the patches were “erinea” which are a mass of enlarged plant hairs caused by the feeding of mites.
He could not find any mites on the specimens that may have caused this, but a search of the literature came up with the name of a mite called Phyllocoptes goniothorax that causes an “erineum” consisting of dense abundant hairs on hawthorn. So, he suspected it was the culprit.
Last year, the leaves of the hawthorn did turn blackish and dry, but the shrub survived. However, the pink fuzz is back again this year.
If anyone happens to see a black hawthorn, please check the back of the leaves. If you discover the same fuzz, please let me know as I would like to keep a record of how widespread this is.
Email: rpojar@gmail.com
