Controlling Weeds in Your Lawn

Controlling Weeds in Your Lawn

Bill Sevier: Master Gardener

Tuesday, May 9, 2017

Q: What is the best way to get rid of weeds in my lawn? J.A., Tulsa

A: The most effective way to prevent weeds is to have a green, thick, healthy lawn, which will prevent weed seeds from sprouting. Unfortunately, most of us don’t have a uniformly thick lawn and have to deal with weeds growing in the thin or bare spots. There is a wide range of tolerances for weeds in the lawn. The purist wants no weeds while others may adhere to the adage “one man’s weed is another man’s wildflower.”

OSU’s lawn maintenance information sheets — one on Bermuda, the other on fescue — are available on the Master Gardener website, tulsamastergardeners.org, in the lawn and garden section. These sheets describe all aspects of lawn care, including weed control, and may contain all the information you need for your lawn care.

In terms of chemical control, there are two approaches — prevention with pre-emergent herbicides and eliminating existing weeds with the post-emergent variety.

Pre-emergent herbicides are best used in the spring to prevent crabgrass and most summer weeds and again in fall to deal with the winter weeds such as henbit, chickweed and annual bluegrass (Poa annua). Pre-emergent herbicides recommended by OSU are listed on the above referenced information sheets. It should be understood that when using these herbicides, you will never get 100 percent prevention, and they will be of no benefit unless the instructions are followed in detail.

Post-emergent herbicides available are based on the type of weed. There are three main botanical weed types — broad leaf, such as dandelion; grassy weeds such as crabgrass, and sedges like yellow nutsedge (nutgrass).

Most broad-leaved weeds are best treated with one of the many brands of herbicides containing a chemical called “2,4-D.” It usually is mixed in with other herbicides to enhance control. The chemicals in this category are mostly derivatives of plant growth hormones and have the greatest effect on growing weeds in spring and fall. After a weed reaches maturity and blooms or produces seeds, their effectiveness is greatly reduced.

Grassy weeds are difficult. The best herbicide for weeds such as mature crabgrass, Dallisgrass, orchard grass and the like has been taken off the market. Herbicides available now for mature crabgrass contain a less effective but useful chemical called quinclorac.

The most common sedge in the lawn is yellow nutsedge. This is the slender weed that pokes its head up above grass two days after mowing. Although some broadleaf herbicides are labeled for nutsedge, they are not effective. Products containing imazaquin (Image), halosulfuron (Sedgehammer) and bentazon (Basagran) and sulfentrazone (many brands) are effective.

Again, suggestions by OSU about which chemicals to use and when are in the lawn maintenance documents from the Master Gardener website mentioned above. Be aware that the chemical names mentioned are found in many brands. Also, remember to always read and follow instructions on the label of each brand.

Garden tips

·        Nutsedge weeds are emerging now. Post-emergent treatments are best applied for the first time this month. Make certain warm-season grasses have completed green-up. Nutsedge requires specific treatment for control; standard broadleaved post-emergent herbicides are not effective. Contact the OSU Tulsa County Master Gardeners for recommendations.

·        Plant summer bulbs such as cannas, dahlias, elephant ear, caladiums and gladiolus.

·        Apples and other fruit need thinning for best production. If apples are not thinned, the crop will be of poorer quality this year and small next year. Thin to one apple every 4 inches.

·        Remember, working wet soil will cause significant damage to the soil structure. Give it time to drain from recent rains, before tilling. Damage from tilling while wet may last for a long time.