P.L. 101-646 - Nonindigenous Aquatic Nuisance Prevention and Control Act of 1990

• http://uscode.house.gov/download/pls/7C61.txt
  This US code expressly prohibits the interstate commerce of noxious weeds and allows for the warrant less search and seizure of said weeds.  This law also deals with the required management of noxious weeds on Federal lands. 

• http://uscode.house.gov/download/pls/18C3.txt
  (a) Whoever knowingly delivers or receives for transportation, or transports, in interstate commerce, alligator grass (alternanthera philoxeroides), or water chestnut plants (trapa natans) or water hyacinth plants (eichhornia crassipes) or the seeds of such grass or plants; or   
  (b) Whoever knowingly sells, purchases, barters, exchanges, gives, or receives any grass, plant, or seed which has been transported in violation of subsection (a); or   
  (c) Whoever knowingly delivers or receives for transportation, or transports, in interstate commerce, an advertisement, to sell, purchase, barter, exchange, give, or receive alligator grass or water chestnut plants or water hyacinth plants or the seeds of such grass or plants -    Shall be fined under this title, or imprisoned not more than six months, or both.