Gall/Pest on Hawthorn ?

Gall/Pest on Hawthorn ?

Observation - Gall/Pest on Hawthorn ? - UK and Ireland. Description: Notice this fluff on a hawthorn seedling. Plant was about 75mm high next to a second plant that was not covered. Anyone have any ideas on what this is caused by ?

Notice this fluff on a hawthorn seedling. Plant was about 75mm high next to a second plant that was not covered.
Anyone have any ideas on what this is caused by ?