Japanese Knotweed

Hello, gardening amateur here, got an allotment a month ago, making progress but this plant keeps cropping up. Until tonight I just assumed it was bindweed but I’ve used a plant I.D app and it says it’s Japanese knotweed, however upon googling Japanese knotweed the photos don’t have the red rimmed leaves that my plants do.

It grows rapidly but that maybe due to the amount of rain and sun we have had. 

So firstly what is it please and secondly how do I go about managing it?

thanks in advance for any responses.