Instructions on Using Herbicides


Gardeners wage a continual battle with weeds, using an array of weapons in their stockpile. Although not recommended for small weed problems, herbicides can be effective in restoring the health of your lawn or garden. Before getting started with herbicides, identify the weed types, purchase an appropriate product and read all labels carefully.

Cultural Weed Management

  • Cultural weed control methods are just as effective and more environmentally friendly than chemicals. Before resorting to herbicides, pull weeds by hand after a rain when the soil is loose. Mulch around plants with 2 to 4 inches of wood chips, straw, pine needles or grass clippings to keep soil moist and prevent weed germination. For warm-season vegetables like squash and tomatoes, use plastic mulch by cutting holes for plants and placing it over the soil, or for flowers use fabric weed control in a similar manner.

Pre-emergence Herbicides

  • Use pre-emergence herbicides before weeds germinate and emerge in your garden or lawn. For summer annual weeds like crabgrass, apply in early spring. For annual winter weeds like bluegrass, apply in late summer. These are good for persistent undesirable annual grasses or broadleaf weeds and can be used near trees, shrubs, in flower beds and around some fruit and vegetable plants, depending on the product. Products containing benefin will kill most annual weeds and work well for crabgrass in lawns. For annual garden and lawn weeds, trifluralin is a good choice. To kill crabgrass, spurge, oxalis and annual bluegrass, use a product that contains dithiopyr, but avoid using it on desirable turf like fine fescue and bentgrass. Aerate the soil before using pre-emergence herbicides, and avoid reseeding desirable grasses for two to three months after use.

Post-emergence Herbicides

  • Once weeds are growing, you must use a post-emergence herbicide for effective control, preferably on young weeds. Selective post-emergence herbicides will only kill certain kinds of weeds. A 2, 4-D product will control dandelions and other broadleaf weeds in lawns. Dicamba will get rid of clover and other broadleaf weeds. Fluazifop can be used in landscapes and beds to kill undesirable grasses such as bermudagrass. Nonselective post-emergence herbicides will kill most types of weeds that have already begun growing. They are especially good at killing perennial weeds. Products containing glyphosate are a good choice because they control most types of weeds and can also be used as spot applications near trees, flower beds, shrubs, patios and driveways. Avoid using post-emergent broadleaf weed killers on windy days as they can easily drift onto other desirable plants and cause damage.

Tips, Risks and Precautions

  • When choosing a product, select the easiest application method because it is typically the safest. Wand and wick applicators can increase the likelihood of targeting only weeds. Read all labels carefully and only use herbicides for the weeds they are intended for and at the rate described. According to Purdue University Cooperative Extension Service, the use of herbicides in vegetable gardens is typically not recommended, although some pre-emergence selective herbicides can be used. When disposing of herbicides, avoid pouring them out in sinks, drains or toilets and instead use all of the product or dispose of it at an official hazardous waste disposal site.

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