There is a troubling discrepancy between the large number of harmful invasive plant species and the number of invasive plant species that are actually regulated. At the federal level, the USDA's Animal and Plant Health Inspection service (APHIS) includes 112 plant species on the Federal Noxious Weed List.Scientific estimates, however, put the actual number of introduced invasive species at around 5,000. It is estimated that annual costs attributed to invasive plant species in the U.S. approach $25 billion.
At the state level, Illinois has two weed laws that attempt to regulate the spread of invasive weeds species within the state's ecosystems; the Illinois Noxious Weed Law, overseen by the Illinois Department of Agriculture, and the Illinois Exotic Weed Act, which is a conservation act enforced by the Illinois Department of Natural Resources. While both statutes attempt to control invasive weed species in the state, the Acts can be differentiated by how the legislature defined noxious and exotic. The Noxious Weed Act defines noxious weeds as "any plant which is determined by the Director...to be injurious to public health, crops, livestock, land or other property." Under the Noxious Weed Act, any weed found on the list must be controlled and eradicated at the cost of the landowner, with a clear focus on protecting agricultural productivity.