Missoula County Weed District & Extension

Herbicides

Herbicides create powerful disturbances in a plant community and should only be used as part of a well thought out integrated weed management plan. The goal of the management plan should be to perpetuate a desirable plant community. Herbicides by themselves may start to move a plant community to a desirable state by removing undesirable plants or weeds from the community. If the niches left by removing undesirable plants from the community are not revegeted with desirable plants, they will likely be filled by other undesirable plants like cheatgrass.

Herbicides are chemical compounds that kill or inhibit the growth of plants. Herbicides are one of the many tools used to control Noxious Weeds. Herbicides are classified as either selective, nonselective, contact or systemic.

  • Selective herbicides have the ability to attack weeds while preserving crops or most beneficial grasses.
  • Nonselective herbicides control all types of vegetation and are used to remove the vegetation from an area. An example of a nonselective herbicide is Roundup ®.
  • Contact herbicides are absorbed by the green growing part of a plant (i.e. leaves, flower, stem) and do not move into the roots of the plant. Annual plants are usually controlled by contact herbicides while biennial and perennial plants usually regrow if treated with a contact herbicide.
  • Systemic herbicides move through a plant in two ways. Systemic herbicides can either move from the green growing parts of a plant to the root or move through the soil to the root and then up to the green growing parts of the plant. Systemic herbicides can be used when trying to control annual, biennial or perennial (link to definition page) plants.


To view a list of commercial applicators currently working in Missoula County area, click here. 

Ensuring that your backpack, ATV or truck sprayer are correctly calibrated ensures that you are applying the right amount of chemical to the plants that you are treating.  Check out our Weed Calibration Video series:


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