Growings On: Troublesome summer weeds

Roger Gates

Adequate moisture and hot daytime and warm night temperatures provide an ideal growing environment for a number of plants. Two plants that may aggravate homeowners are common bermudagrass and nutsedge. Both plants thrive during midsummer.

With appropriate management, bermudagrass may provide useful low-input pasture for livestock or some low maintenance lawns. In other locations, it is not desirable as it is not attractive and may compete with desirable ornamentals or fruits and vegetables.

Short stature and prolific horizontal stems called stolons make bermudagrass relatively easy to recognize. Unlike sterile hybrid bermudagrass varieties, used for productive pasture and high quality turf, common bermudagrass produces fertile seeds. However, stolons or runners are the primary mechanism by which it reproduces and spreads. These tenacious runners and extensive rooting structure make hand weeding very difficult. Hand pulling bermudagrass will inevitably leave behind vegetative structures from which the plant will rapidly recover.

In addition to moisture, warm temperatures and limited nutrients, which cannot be controlled, bermudagrass thrives in full sunlight. Many desirable ornamentals and vegetables are also most productive in full sun. Selectively eliminating exposure to light provides one approach to controlling bermudagrass. Covering the offending plant with a layer of mulch will eliminate the light exposure. Cover the entire infestation with several inches of mulch. Wood chips, pine straw or similar materials can be used. Adding a layer of newspaper, cardboard or landscape fabric below the mulch may improve effectiveness. Hay and grass clippings may contain weed seeds, and should not be used as mulch.

Bermudagrass stolons and roots accumulate nutrient reserves and will continue to grow, attempting to reach a source of light. Time will be required to exhaust these reserves, so continuing alertness to cover newly emerged leaves and stolons will be necessary. Mulch should remain in place for at least two growing seasons to eliminate tough perennial grasses like bermudagrass.

Nutsedge can be recognized by its yellow green color and slender leaves. Sedges are described by botanists as “grass-like,” because they are not true grasses. A unique characteristic of sedges that also helps in identification is the leaf arrangement. Unlike grass leaves, which are arranged on opposite sides of the stem, sedge leaves are arranged in a triangular pattern. When a grass stem is rolled between the fingers, it is usually round. The triangular pattern of a sedge plant can also be detected and leads to the description, “sedges have edges.” Sedges usually occur as solitary plants, but, like bermudagrass, has below ground structures, tubers, which accumulate stored nutrients. Nutsedge also spreads vegetatively with horizontal stems below ground called rhizomes. Nutsedge is equally difficult to control with hand weeding.

A layer of mulch to limit light exposure may weaken nutsedge, but its upright growth and pointed leaves allow it to emerge through most layers. Nutsedge may even penetrate through a new layer of asphalt.

Where mulching is not effective or not appropriate, weeds may be controlled using selective herbicides. To control bermudagrass in vegetable gardens, use an herbicide containing the active ingredient sethoxydim (brands such as Poast and Vantage) around broadleaf vegetables. This product cannot be used around corn, however, as corn is in the grass family and will be damaged. This chemical is very selective for controlling grasses and will not control other weeds.

There are also product options on the market that can be used in flowerbeds to selectively control weedy grasses, including bermudagrass. Products containing the active ingredient clethodim (Envoy), fluazifop-p-butyl (Grass-B-Gon and other brands) or sethoxydim (Segment) are safe around most flowers and shrubs.

Nutsedge is not a grass and requires a different selective product that contains imazaquin (Image) which can be applied over the top of a number of ornamentals. Be sure to read the label to determine which plants are safe to spray and which will be injured.

A nonselective herbicide containing glyphosate (brands such as Roundup and others) can also be used in between rows and along borders of vegetable gardens and flowerbeds. However, because this is a nonselective herbicide, avoid any direct contact or spray drift with desirable plants. A number of products are currently labeled “Roundup” and may contain herbicides mixed in addition to glyphosate. Be certain that the product you select contains only the active ingredients appropriate for the intended use.

Because bermudagrass and nutsedge are perennial plants and accumulate nutrient reserves for regrowth, it is possible that they will recover from a single application of a nonselective herbicide, requiring additional applications.

Be sure to read and follow all labeled application rates and safety precautions when using herbicides.

Roger Gates is the agricultural and natural resources agent for University of Georgia Extension, Whitfield County. Contact him at roger.gates@uga.edu.

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