Choosing a Herbicide

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A weed is a plant out of place. A herbicide is a material to control weeds if cultural practices have failed to control weeds. Weeds in lawns are generally grass type plants such as crabgrass or broadleaf plants such as dandelions. When choosing a herbicide you need to identify the weed that you want to control. Once you identify the weed you can find out what type of herbicide would work best.

There are three types of herbicides available. Premergence herbicides affect the germinating seeds. They need to be applied two to three weeks before the seeds germinate. Premergence herbicides are the most effective against annual weeds such as crabgrass. Postemergence herbicides are used to control weeds after the plants are up and growing. Postemergence herbicides are selective herbicides. This means they are formulated to control weeds and not harm your grass. Selective postemergence herbicides are available for broadleaf weeds, annual grasses and nutgrass. Nonselective postemergence herbicides can kill all plants, both desirable and undesirable. These herbicides can be used to spot treat areas. You must use caution not to spray nonselective herbicides on plants you want to keep.

Remember, before you select a herbicide, identify the weed you want to control. Your county Extension office, master garden office or lawn and garden center can help you identify weeds. When selecting a herbicide read the label and find a listing for the weed you want to control. Follow the label directions for application.

Tom Fowler, FowlerT@missouri.edu
Regional Specialist, Agriculture and Horticulture
Buchanan County, MO
University of Missouri Extension