Killing Broad Leaf Lawn Weeds

Killing broad leaf lawn weeds is best handled with a post emergent, selective herbicide. It eradicates only the weeds, not the grass.

However, it is not enough to kill the weeds in your lawn and call it a day. You need to replace those weeds with new grass because your existing lawn will not spread quickly enough to fill in the bare spots by itself.

Common Broadleaf Weeds

Broadleaf weeds include the dandelion, plantain, clover, chickweed, buckthorn, dichondra, ground ivy, oxalis, knotweed, purslane, and prostate spurge.

Herbicides for Broadleaf Weeds

There are a number of selective herbicides on the market for killing broad leaf lawn weeds without harming turf grass. Garden centers sell these chemicals under different brand names. Regardless of the brand name, the active ingredient on the label should list either 2,4-D, MCPA, MCPP or Dicamba.

  • 2,4-D (Dimethylamine Salt of 2, 4-Dichlorophenoxyacetic acid) is a growth regulating hormone compound. It is not a persistent pesticide in the soil. In somewhat warm soil, its half life is 2 weeks or less. 2,4-D is not a persistent pesticide in water. There is 90% disappearance in less than 2 weeks. It decomposes in sunlight.
  • MCPP (mecoprop: 2-methyl-4-chlorophenozypropionic acid). This is similar to 2,4-D but is safer to use on new lawns or sensitive grasses such as bent grass or St. Augustine grass.
  • MCPA (2-methyl-4-chlorophenoxyacetic acid)
  • Dicamba (Dimethylamine Salt of Dicamba (3,6-dichloro-o-anisic acid) is frequently used against clover, chickweed, and knotweed. Dicamba affects plant hormones. It is absorbed through the roots and leaves. Do not use products containing this ingredient around trees and shrubs, which also may absorb it through their roots. Dicamba is used in mixtures with other herbicides such as 2,4-D and MCPP. It stays active in the soil.

There are several preemergent herbicides for preventing broadleaf weeds from growing in the first place (ie: Isoxaben). Sometimes they are mixed in with fertilizer for spring applications. They kill weed seeds before they sprout. However, most lawns still require post-emergent weed control applications.

Do not allow children or pets to walk on the lawn the day the herbicide is sprayed on the lawn. These chemicals are powerful and toxic, otherwise they would not do the job of killing weeds.

If you get tired of killing broad leaf lawn weeds or don’t want to be exposed to pesticides, have a local lawn treatment company do it. I like how you can sign up online for a free estimate.

Plant Grass to Replace Broadleaf Weeds

After a herbicide has effectively killed the areas of your lawn with weeds, there is going to be much bare space. Wait at least 2 weeks before planting grass seed in those bare spots. Don't wait much longer than that because new weeds will try to move in.

In the fall, you can plant your choice of grass--bluegrass, tall fescue, or perennial rye. It will have plenty of time to germinate, develop strong root systems and grow to 2 inches before the soil warms enough next spring to sprout weed seeds.

In the spring, fill bare spots with quick-germinating perennial rye, which will beat the weed seeds to the punch.

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