Much of the land in heavily populated North Texas contains residential homes with lawns. Homeowners, trying to keep green and attractive lawns, wage a constant battle against weeds that compete with turf grass for water, sunlight and nutrients. The best defense against warm-weather lawn weeds is a healthy stand of grass. The weeds that appear in dormant grasses during colder weather must be dug out, treated with herbicide, or stopped, using preemergent weed killers.
Dallisgrass is a perennial weed that forms dinner-plate-sized clumps of grass. The dark-green foliage has seed stalks that emerge a few days after mowing. Dallisgrass moves through lawns by both rhizomes under the soil and by seeds. Because of its clever means of self-propagation, it cannot be controlled with a preemergent weed killer. Dallisgrass must be spot-treated with a postemergent herbicide such as DMSA or MSMA applied in late May or early June. Do not use DMSA- or MSMA-containing products on St. Augustine lawns. For St. Augustine grass, spot-treat during the summer with a general herbicide such as glyphosate that kills any plant it touches.
Henbit is a broadleaf, winter annual weed with pinkish-purple or blue flowers arranged in whorls between the stem and the upper leaves. Stems are upright and slightly square with opposite leaves. Because it blooms in the late fall, it is easy to notice since weeds are likely to be the only green in the grass. Henbit is controlled with a preemergent herbicide in the fall. If the plant has emerged, treat it in Bermuda grass with a product containing 2,4-D. Control of henbit in St. Augustine has been successfully accomplished with atrazine. However, many people are concerned about unintended health effects of this chemical. Before putting a postemergent herbicide on St. Augustine, read the product label carefully to make sure it is appropriate for St. Augustine grass.
Chickweed is a broadleaf, winter annual that spreads quickly. The plant has white flowers arranged in five sets with two petals each. It grows close to the ground with oval or elliptical leaves that are arranged opposite along the stem. The leaves are generally light green with smooth edges. The leaves at the base of the plant may be slightly hairy. Chickweed may be pulled by hand, treated with a preemergent herbicide before the seeds germinate, or removed with a broadleaf weed killer in Bermuda grass. You can use a general-purpose herbicide such as glyphosate on St. Augustine grass, but be careful to not get the spray near desirable plants.