I looked up ‘Old Michaelmas Day’ and, according to various sources, it’s either 10 October or 11 October. Either way, according to folklore it’s definitely the last day to safely pick blackberries. I heard years ago that the Devil swept his cloak over the land in October, making the fruit bitter. Other legends relate Lucifer’s Fall in October, landing on a blackberry bush and cursing the fruit. More prosaic explanations include damp weather, and possibly something to do with the life cycle of the caddis fly.
There is a brilliant mug with old Wiltshire dialect words in the shop at Wiltshire Museum, Devizes (link to their website below) including ‘Pack Rag Day’ for Old Michaelmas. Pack Rag Day seems to relate to servants or agricultural workers moving and finding new employers at hiring fairs. So maybe that’s why the first of the Marlborough Mop Fairs is held on this particular weekend in October.
The scientific study of brambles, or Batology, has origins in the 18th century. Apparently in those early days all British blackberries were lumped together as one species. In An Early History of Batology in Wiltshire (1999), Rob Randall reveals that the earliest known reference to a Wiltshire plant when Donald Grose was compiling his county flora was in a grant of land by King Cenwalh in 672 AD, probably at South Newton, which refers to a ‘brember wudu’. Grose explains “the same Bramble Wood is mentioned in six of the Wiltshire Charters but the site is not determinable” (Grose 1957, p 223).
Thanks to Mr Randall we have a list of brambles collected by Miss Emily Sophia Todd (1859-1949) part of that lady’s “formidable herbarium” at Swindon Museum & Art Gallery. Miss Todd lived at Hampstead Cottage in Aldbourne and collected a vast amount of flora. Including brambles from all around the country, but apparently she “rarely travelled more than a few miles from her home at Aldbourne when collecting Wiltshire material [brambles].”
when Donald Grose was preparing the account of brambles for his Flora in 1948-9 he invited William Charles Richard Watson (1885–1954) to Wiltshire for some field work. During this period Watson checked the brambles in the Todd herbarium.”Rob Randall* Wiltshire Botany 2, 1999 An Early History of Batology in Wiltshire
* This gentleman is very possibly the same Rob Randall. Dr Steve Wharton’s oration on Robert Randall for the honorary degree of Master of Arts in December 2014 https://www.bath.ac.uk/corporate-information/robert-randall-oration/