Winter weeds in Central Texas lawns

The green weeds in a Central Texas lawn this month are most likely winter annuals such as henbit, chickweed and annual bluegrass. They stand out because the St. Augustine or Bermuda around them is shutting down for the year. By November a pre-emergent is too late for this crop, so the job now is keeping them from going to seed and planning the fall application that heads them off next year.

What are the green weeds in a dormant lawn?

Winter weeds are annuals that run on the opposite schedule from your grass. AgriLife's Bermudagrass calendar says henbit and rescuegrass germinate in late summer or early fall, grow through fall and winter, then flower, set seed and die in spring. AgriLife Today adds annual bluegrass, chickweed, Carolina geranium and lawn burweed to the list of lawn regulars.

You notice them now because the color around them is leaving. AgriLife's St. Augustinegrass guide says the grass turns brown or off-colored during winter dormancy, and the National Weather Service Austin climate summary puts the average first freeze at December 1. A weed that was hidden in September sticks out in January.

How do you tell which winter weed you have?

Sort it into broadleaf or grassy first, because the products that control each one differ. AgriLife gives a simple way to look at it:

• Broadleaf weeds: net-like veins in the leaf. AggieTurf describes henbit as square-stemmed with pinkish to reddish purple flowers.
• Grassy weeds: parallel veins and long, slender leaves. Annual bluegrass and rescuegrass fall here.
• Lawn burweed: low to the ground. AgriLife Today says it typically goes unnoticed until someone steps on the tiny stickers.

If you are still not sure, AgriLife's AggieTurf site keeps an image gallery of over 100 common Texas weeds.

Is it too late to treat winter weeds in November?

It is too late for a pre-emergent, but not too late to do something. AgriLife says pre-emergence herbicides will not control weeds adequately after they emerge, and the fall window opens when soil temperature drops to about 70 degrees for 4 or 5 consecutive days. The Williamson County Extension office puts that at early to mid-September in this area. These weeds are already up, so a pre-emergent spread today does nothing for them.

Pull or spot-treat while they are small

Pull them by hand or spot-treat them, which is what the Williamson County office advises for weeds that are actively growing. AgriLife says annual broadleaf weeds are easily controlled with post-emergence herbicides while they are small and before they flower, and that herbicides applied to flowering weeds late in their season may not be effective.

Read the label for your grass before you spray. AgriLife's St. Augustine maintenance guide says St. Augustinegrass is very sensitive to some herbicides, such as 2,4-D. The Bermudagrass calendar also says these products belong on healthy, actively growing turf, which is a poor description of a lawn going dormant, so on a mostly brown yard hand-pulling is the safer call.

Mow them before they go to seed

Mowing slows winter weeds down once they are up. AgriLife's mowing guide says regular mowing while winter weeds are active helps regulate them, and that removing flowers and seedheads limits how far they spread. Bag those clippings instead of mulching them back in, because the same guide says clippings with weed seedheads should be collected and removed. Our mowing maintenance crews can keep on top of this through the cool months.

Skip the weed and feed

Leave weed and feed in the garage until spring. AgriLife turfgrass specialist Chrissie Segars does not recommend it as a fall or winter product, because nitrogen pushes growth just as a quick freeze could damage it. She says the last nitrogen should go down 4 to 6 weeks before the average first frost. Against Austin's December 1 average, that deadline had passed by November 3.

Do you have to kill winter weeds at all?

No. Winter annuals die on their own once they finish flowering in spring, and AgriLife notes it may not be worth the time and expense to control a weed that will die naturally within a few weeks. What you would be stopping is the seed they drop on the way out. Burweed in a yard where kids or dogs play is worth dealing with sooner.

How do you stop winter weeds next fall?

Put a fall pre-emergent on the calendar, because a spring application will not cover it. The Bermudagrass calendar says that even if you treat in spring for summer weeds, you must treat again in fall for winter annuals. AgriLife's preemergence guide recommends two applications a year, with spring at about 55 degrees soil temperature. Here is what the fall one takes:

• Check the soil, not the date: measure the top 1 inch of soil with a soil or meat thermometer. Segars warns against relying on the same calendar date every year.
• Match the product: the county office says to pick for your grass type first, then the weed. Dithiopyr, pendimethalin and prodiamine handle grassy weeds, isoxaben handles broadleaf, and you might need two separate products.
• Water it in: AgriLife Today says granular products typically need one-quarter to one-half inch of water to dissolve properly.
• Know when to hold off: skip it if you plan to overseed with ryegrass, or if the turf is under moderate to severe stress.

Some homeowners would rather not handle any of this, and Segars says those homeowners should call a local landscape professional. Our lawn treatment service matches weed control to the season and your turf type.

Why do some lawns get more winter weeds than others?

Thin grass is the likely reason. AgriLife calls a dense, healthy lawn the best defense against weeds and says to find the cause of the thinning before treating. Its St. Augustine maintenance guide goes further and says winter annual weeds are not common in St. Augustinegrass at all, so a St. Augustine yard full of them is telling you something about the turf.

Scalping makes it worse. AgriLife's St. Augustinegrass guide says frequent scalping raises the odds of weed encroachment by exposing soil to sunlight, while a taller mowing height helps shade weeds out.

If your yard in Georgetown or nearby is greening up with the wrong plants this winter, the plan is short. Pull or spot-treat what is small, mow off anything starting to flower, and mark early September on next year's calendar.

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