Michaelmas maps onto the autumn equinox. “Harvest” is too generic – the harvest goes on for a long time, you know? – but I like to think of it as the appropriate pivot point from apple and blackberry to pumpkin.
There are traditions around the dangerous field spirits that retreat further and further into the grain as it’s harvested. The last straws are made into a ceremonial wreath and delivered to the landowner, who gets to / has to keep it over the winter. My father views this as appropriate spiritual payback; you could also view it as an extension of manorial obligations of protection.