Mike: It certainly looks like Japanese knotweed. J. knotweed is a prohibited species in MI. I am waiting to hear back from MDARD about who is the person to contact regarding issues similar to this, but their Customer Service Center is 1-800-292-3939. MDARD is the regulatory agency for prohibited and restricted weeds.
From MDARD Website: http://www.michigan.gov/mdard/0,4610,7-125-1569_16993-11250--,00.html
"Michigan laws regulate the possession and sale of certain plant species which are considered undesirable from agricultural as well as environmental viewpoints. These unwanted species are listed below according to the applicable laws and regulations."
A. Prohibited Plant Species (Natural Resources and Environmental Protection Act (Act 451 of 1994, as amended)
Prohibited species identified under this Act cannot be sold or grown in the state. Any of the following plants, fragments, seeds or a hybrid or genetically engineered variant thereof are specifically prohibited.
Cabomba caroliniana - Fanwort
Cylindrospermopsis raciborskii - Cylindro
Egeria densa - Brazilian elodea, also known as Anacharis
Fallopia japonica - Japanese knotweed
Heracleum mantegazzianum - Giant Hogweed
Hydrilla verticillata - Hydrilla
Hydrocharis morsus-ranae - European frogbit
Lagarosiphon major - African oxygen weed
Myriophyllum aquaticum - Parrot's Feather
Nitellopsis obtusa - Starry Stonewort
Nymphoides peltata - Yellow Floating Heart
Salvinia molesta, auriculata, biloba, or herzogii - Giant Salvinia
Trapa natans - Water Chestnut