It has been here for some time. It likes disturbed ground but will grow anywhere, and fast. Probably 15 years ago I was hacking it out of my neighbor's stone wall that was of no concern to him. Odd place for it but it grows well anywhere. Also, it is harvested by herbalists as a treatment for Lyme and related infections. (Just enter Knotweed and Lyme in Google).
Never seen that one luckily, but invasives are really taking over in some otherwise pristine parts. Around here, honeysuckle is probably the biggest problem - I've spent almost every warm weather weekend outside for a few years pulling that stuff from my yard and it's just now mostly gone. That species was introduced by the government, and if you look at state parks, they are all overrun with honeysuckle. Not to take a tired anti-government role on something like this, but they can start a problem yet can't be bothered to help with removing it.
Bradford pear has been disasterous for flowering wild fruit trees. Kudzu may be holding Alabama together, but in many places it's a plague. Nandina berries kill birds that feed on them. And on and on............All these have in common that they are not native to this country.
Asian Lady Beetle
Green Ash Borer
about umpteen thousand more