How to Control Weeds in the Lawn

Identifying weeds, how to treat them

Bill Sevier: Ask a Master Gardener

Wednesday, January 20, 2016

Q: I have weeds in my Bermuda that have wide leaves and look like dandelions. How can I identify this weed and decide what herbicide to use? M.S., Jenks.

A: The practical answer to this question is that you generally do not need to know the specific identity of a plant to decide what herbicide might be best.

Any green weed located in fully dormant Bermuda (brown when dormant) can be sprayed with glyphosate, an herbicide found in Roundup and many other brands. It will kill any green plant in Bermuda and can be done without risk to Bermuda grass during most Januarys and Februarys. However, glyphosate cannot be used on zoysia lawns at any time, dormant or not.

For weed control in general there is no need to specifically identify a weed, one need only to decide what category of weeds it is in. There are three types of weeds in lawns — grassy weeds, broadleaf weeds and sedges. Each category has certain herbicides that are recommended for their control.

Grassy-type weeds are those that have leaf veins parallel to each other such as found in crabgrass. Grass-specific herbicides are available, some of which may be safe to spray on ornamentals and even in the vegetable garden.

Sedges are plants that usually have triangular stems leading to the aphorism “sedges have edges,” making them fairly easy to identify. A sedge commonly found in lawns that is difficult to control is yellow nutsedge. Nutsedge and other sedges have specific herbicides, which are useful.

Broadleaf weeds are those with fan-like veins. This is a huge category of plants such as dandelions, henbit and wild strawberries. The herbicides, which often contain a mixture of chemicals such as 2,4-D, are specific for these broad leaf weeds, have no effect on grasses and often little or no effect on sedges. They are effective when used properly.

Timing is often critical for best effect of herbicides. Most of the chemicals used for broad leaf weed control are modified growth hormones. They are most effective when the weeds are actively growing, usually either spring or fall. After weeds have reached maturity with flower and seed production, there is less linear growth and less herbicide effect.

So the key to weed control is to have the healthiest lawn possible and, if needed, use a herbicide specific for the category of weed at the proper time. There is usually no need to know the specific name of a weed, you just need to know the category.

For information about general care needed for best lawn care, go to the turfgrass section of the Master Gardener website and look for the Bermuda and the fescue Maintenance Calendars. These documents have recommendations, what to do and when to do it, for optimal lawn care in Oklahoma.

Garden tips

§  Make sure indoor plants are receiving enough light or set up an indoor fluorescent plant light.

§  Till garden plots without a cover crop to further expose garden pests to harsh winter conditions.

§  Visit the Master Gardeners office at the OSU Tulsa County Extension Building to obtain gardening fact sheets for the new gardening season. The office is located at 4116 E. 15th St.

§  Choose fruit varieties that have a proven track record for Oklahoma’s conditions. OSU fact Sheet HLA-6222, “Home Fruit Planting Guide” has a recommended list.