Weeds of Missouri

Danger

• Weeds are a nuisance and not only because they reduce the productivity of crops. Weeds will reduce land values, obstruct access to utility lines, overrun forest nurseries, destroy wildlife habitat and injure grazing animals. For instance, wetlands in Missouri that are infested with loosestrife, a noxious weed, can lose up to 50 percent of native plants. Another problem with weeds is the cost to the environment in herbicides to control them. According to estimates by the Missouri Department of Agriculture, 97 percent of pesticides are used as herbicides to kill weeds.

Perennial Weeds

• Perennial weeds live three or more years. The main noxious perennial weeds in Missouri are the Canada thistle, the field blindweed, the Johnsongrass, the Kudzu, the multiflora rose and the purple loosestrife. Most of these weeds were introduced in the United States by Europeans as part of contaminated crop seed. Two exceptions are the Johnsongrass and the Kudzu, which were introduced as forage and in the case of Kudzu, also for its ornamental value.

Annual Noxious Weeds

• Marijuana is the main annual noxious weed in Missouri, although some may debate if a plant so desired and widely used can be considered a nuisance. Annual weeds, like the Marijuana plant, will complete its life cycle within one year. A classic example of an annual weed is crabgrass, which germinates in the spring and dies in the first hard frost of every year.

Biennial Noxious Weeds

• Biennial plants live for two seasons but rarely flower and produce seed until the second year. In Missouri this includes the musk thistle and the Scotch thistle. The musk thistle has spiny leaves that can reach up to 6 1/2 feet high and is mainly found as a weed in pastures and hay fields. For example, the musk thistle has erect and branched stems that produce solitary flower heads in the second year.