The topic appears to be of considerable interest, thanks to contributions I am learning.
Since more than one possible cause has been put forward I am reserving my finger pointing.
For background interest I have selected some internet stuff. It may be necessary to copy and paste to search.
First one ‘scale mites’, then ‘2,4-D’, then ‘smoulder’. I am sure some keen Daffnetters are already well up to speed on these, I’m just starting.
George Norris Scotland
www.pan-uk.org/pestnews/Actives/24d.htm pick fact sheet