Pests in Gardens and Landscapes: Quick Tips

Weed Control Using Herbicides

Published   5/16

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Most weed problems in gardens can be managed by hand-weeding, mulching, good garden design, keeping lawns vigorous and competitive, or using other nonchemical methods. However, gardeners sometimes choose to use an herbicide (a chemical weed killer) to control weeds. When using herbicides, follow label directions precisely. Otherwise products will fail to control the weeds, and may damage desirable plants, or limit your ability to replant. Too much herbicide also wastes money and gets carried away in runoff water. Follow herbicide treatments with longer-term nonchemical methods such as installing mulches, modifying irrigation, pulling weeds, or filling cracks.

Identify the weed and select the proper herbicide for the application site.

  • Be sure the label lists the weed you want to control.
  • An herbicide will kill all susceptible plants, not just weeds. Make sure the label says it’s safe to use on or around the plants in your lawn, garden, or landscape.
  • Be sure the weeds are in a stage that is susceptible to the herbicide. (See preemergence and postemergence below.)

Check the label for the herbicide type.

  • Herbicides that kill most plants they contact are called nonselective.
  • Weed killers that control some kinds of plants but not others are called selective herbicides.
  • Herbicides that control the germinating seeds before plants emerge from the soil are called preemergence herbicides. They won’t control weeds that have already emerged. Use postemergence herbicides to control plants that have already emerged.
  • The younger the weed, the better a postemergence herbicide will work.
Some Common Herbicide Active Ingredients and Their Use
Active Ingredient1 Weeds Controlled Where Used Notes
Most As spot treatments on weeds or clumps of weeds Will injure desired plants if spray gets on them.
Plant oils including clove, lemongrass, and eugenol
Young broadleaves In cracks and crevices or as spot treatments Organically acceptable. Won’t control older weeds or perennials. Best when temperatures are above 70°F.
Most annual weeds Gardens and lawns Water or cultivate soil after applying. Use after garden plants are established.
Most annual weeds Lawns Often used for crabgrass control.
Crabgrass, annual bluegrass, oxalis, spurge,others Lawns Will injure fine fescue and bentgrass.
Broadleaves Lawns Controls clover and other broadleaf weeds in lawns.
Grasses including bermudagrass In broadleaf groundcovers or landscape beds Apply when grass weeds are actively growing.
2,4-D or 2,4-Dichloro-acetic acid
Broadleaves Lawns Controls dandelion and other broadleaf weeds in lawns.
1Some of these active ingredients are sold in combination with other ingredients.

Minimize the use of pesticides that pollute our waterways. Use nonchemical alternatives or less toxic pesticide products whenever possible. Read product labels carefully and follow instructions on proper use, storage, and disposal.

Statewide IPM Program, Agriculture and Natural Resources, University of California
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