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Johnson County

Research-based Information You Can Trust — Localized for your needs

Johnson County
11811 S. Sunset Drive
Suite 1500
Olathe, KS 66061

Office Hours:

Monday - Friday,
8:30 a.m. - 5 p.m.

(913) 715-7000
(913) 715-7005 fax

Map to our office

K-State Research and Extension is committed to making its services, activities and programs accessible to all participants. Reasonable accommodations for persons with disabilities may be requested by contacting Johnson County Extension at (913)715-7000. Notify staff of accommodation needs as early as possible.

Kansas State University Agricultural Experiment Station and Cooperative Extension Service

K-State Research and Extension is an equal opportunity provider and employer.

Weeds in the Lawn

Return to Weed Agent Articles

Out of all the lawn care questions the Extension office receives from homeowners, the number one concern is weeds. The weed each homeowner wants to control is the one that is present in their lawn at that time. In the spring, it’s henbit, chickweed and dandelions. In the summer it’s nutsedge and crabgrass.

Prevention is the best control. But how do weeds invade our lawns?
Unfortunately, the optimal time to control specific weeds is not necessarily when you first see them. In addition, no one product or individual application will control all weeds for the entire season. The best way to control weeds is to prevent them from ever creeping up in your yard. So just why do weeds invade lawns?

  • Improper mowing. Mowing too short can thin the turf stand and allow weeds to germinate and shoot through the canopy.
  • Improper fertilizing. If some is good, more is better, right? Fertilizing too much, too little, or at the wrong time may benefit the unwanted weeds more than the turf.
  • Improper watering. Frequent irrigation encourages weed seeds to germinate and a shallow-rooted turf that is less competitive with weeds for soil moisture and nutrients.
  • Compacted soil. Compaction is a hidden stress for heavy clay soils. The turfgrass root system struggles to compete with weeds in a highly compacted soil.
  • Environmental stress. When the stresses of the environment (i.e. late season freeze, heavy rains and flooding, high humidity) weaken and thin lawns, weeds often take over.
  • Thatch. Excessive thatch results in shallow-rooted grass, which can lead to weed invasions. Soil-applied weed control chemicals can bind up in thatch, reducing their effectiveness.

Fall is the best time to control broadleaf weeds
Late October through early November is the most effective time to control broadleaf weeds in lawns. Dandelions usually produce a flush of new plants in late September, and the winter annual weeds henbit and chickweed germinate in October. These young plants are small and easily controlled with herbicides. Even established dandelions are more easily controlled in the fall than in the spring because they are actively moving materials from the top portion of the plant to the roots. Herbicides will translocate to the roots as well and will kill the plant starting at the roots.

Chemical control of broadleaf weeds
There are some keys to keep in mind when using a chemical control product for weeds in the lawn.

  • Select an herbicide that is effective against the weeds and safe for the turf.
  • Follow all label directions and precautions.
  • Apply the herbicide at the correct time and rate.
  • Apply the product uniformly over the area without overlapping or skips.
  • Repeat the application as specified on the label.

Products such as 2,4-D or combination products that contain 2,4-D, MCPP and Dicamba (Trimec) have been on the market a number of years and provide good results. Newer produces are now on the market and these include Triclopyr and Carfentrazone. Carfentrazone is even effective at lower temperatures allowing for a wider control window. Remember whenever applying any chemical be sure to read and follow all label instructions for best results and safety. Also keep in mind the more active the weed growth, the more effective its control.

Caution should be taken when applying broadleaf weed control to avoid damaging desirable landscape plants. Applications should be avoided on windy days to prevent drift from occurring.

K-State Research and Extension Johnson County Master Gardener logo

Have questions? The Garden Hotline is staffed by trained EMG volunteers and Extension staff who will assist you with questions.

Phone: (913) 715-7050

Email: garden.help@jocogov.org