Hello,

MDARD is the agency that licenses all professional applicators in Michigan. You can check credentials here-

https://www.michigan.gov/mdard/0,4610,7-125-1569_16988_35288-11993--,00.html

Controlling Japanese knotweed of course is not easy, and is not a once and done process. Depending upon how extensive the stand is, it will take multiple treatments to control the plants. Here are articles that discusses how the  plant is controlled. You should know this process so that you can assess  that whoever you hire  is  using the correct procedures-

 https://www.canr.msu.edu/uploads/234/51087/knotweed_BCP_372280_7.pdf

https://extension.unh.edu/blog/when-best-time-control-japanese-knotweed

There are professional garden services available. MSU does not recommend retailers or brands. If you look in local publications, The Michigan Gardener is one example available at libraries and garden centers, you will find ads for garden services . You can search the internet, for example “ professional weed removal” or something similar. Also this link to the Michigan Nursery and Landscape Assoc. may give you some leads-

http://plantmichigangreen.com/aws/MNLA/pt/sp/home_page

If you decide to hire a service, check that herbicides they use are  listed in the  links to control knotweed. Even professionals will  need to tackle the problem with multiple visits and/or applications.