Virtually all the populations of Japanese Knotweed (Fallopia japonica) in Neath Port Talbot are exhibiting catastrophic wilt symptoms.
I brought this to the attention of a few people a few days ago and several people have told me that they have noticed this elsewhere in South Wales. In a walk along along the Neath Canal between Neath and Briton Ferry, almost every plant I looked at was showing severe wilt symptoms (as shown in the photo below). It almost looks as if there has been a mass herbicide spraying event!
I haven't noticed Japanese Knotweed wilting on such a wide scale before and it is interesting to speculate on what is going on here. The rapid onset and scale of this phenomenon suggests that it is not the result of disease or herbivore attack. Rather, it appears to be the result of a physiological shock. But it doesn't appear to be a result of water shortage as such, which might seem to be the most obvious cause given the dry weather we've experienced recently - many plants that are growing in moist soil all along the canal are wilting. One possibility is that the mild conditions of early Spring this year have stimulated an early, rapid growth of tender knotweed stems which have subsequently experienced catastrophic chilling shock injury during the recent, unseasonal cold conditions. It's what happens to your tender half hardy seedlings when you plant them out too early.
I haven't seen this reported elsewhere, nor am I aware of any information on it in the literature, but I suspect it has occurred on a wide scale throughout the UK. Comments welcome.