A lot depends on what happened the previous season. It tends to be endemic on allotment sites because people don't recognise it (they always think it's 'just rotting') and don't cut the foliage back or root out their accidentals, which carry it from the previous year. After those two very wet summers a few years back, late blight was appearing regularly in June on my site. I'm hoping that after last year's drought there's going to be a lot less of it, as I saw very little last year.