CERTIFIED TEXAS EXPERT GARDENER — Herbicides needed for weed control in SETX

Published 12:04 am Wednesday, October 25, 2023

Once again, our local weather has been amazing! In my opinion, this is the perfect time to be outdoors performing all gardening tasks: planting vegetable gardens, tidying up landscapes or sprucing up flower beds.

The only thing missing from our amazing weather pattern: rainfall. Eventually, rain events will return but as we wait, don’t forget to mulch, mulch, mulch-every gardener’s best friend.

Remember seeds need light to germinate, adding 3 to 4 inches of mulch in garden beds will deter weed seed germination and minimize use of herbicides.

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Last week we reviewed weed groups: annuals, biennials, perennials and common turfgrass lawn types for our region. This week (part 2) we are shifting the discussion and determining the best approach for controlling and managing weeds.

Weed control is sometimes complicated but can be achieved utilizing multiple methods. The simplest way to control weeds is to manually dig each one up individually, a good choice if there are only a few in your landscape.

For large areas crowded by weeds (without turfgrass) an option is to cover the weeded area with heavy-duty plastic or a tarp. Allow the cover to remain securely in place 3 to 4 weeks.

Allow the sun’s energy (heat) to destroy the weeds. Using pre- and post- emergent herbicides (organic or chemical) forms can also help gardeners manage weeds.

There are numerous types of herbicides, so let’s ‘dig in’ (pun intended). Note that it’s important we understand the different types of herbicides, how they perform, when to apply them (for best results) and follow application directions.

Gardeners, let me reiterate my point, before using any herbicide please read & follow the manufacturers’ label directions for personal & environmental safety.

Follow the dosage (concentration) and application rates exactly, and never use a greater concentration of herbicide than is necessary.

Pre-emergent herbicides

Apply before weeds germinate. For warm-season annual weeds, apply a pre-emergent herbicide in early spring (Jan-Mar), before the soil temperature reaches 55 degrees F. Weeds that germinate later, during the summer require a second application (Jun-Jul). For cool-season annual weeds, apply early fall (Aug-Nov). Note that this varies year-to-year, completely dependent on our temperature.

Post-emergent herbicides

Apply once weeds have germinated. They are effective when weeds are still small, less than 4 inches high.

Contact Herbicides

As the name implies, cause damage wherever they touch a plant. They must cover all parts of the plant: leaves and stems, including the top and undersides of leaves, to be most effective.

Systemic Herbicides

These types of herbicides are absorbed throughout the plant. They are applied to the soil surrounding the plant’s base, and to the plant itself. They move through the plant-foliage to roots, stems, and other plant parts. These herbicides work exceedingly well on perennial weeds, since the herbicide moves to all parts of the plant, killing the root, tuber, and rhizome growth. Systemic herbicides require more than one application at 6-to-8-week intervals, especially on weeds, which are more difficult to control.

Selective herbicides

Eradicate one type of plant without damaging others. Often a good choice for use on turfgrass lawns, which have a single type of weed problem.

Nonselective herbicide

These types of herbicides are indiscriminate weed killers and will destroy almost any plant they contact. It is imperative to be extremely careful when using these types of herbicides. Dosage and herbicide handling are critical for personal and environmental safety.

Texas A&M AgriLife Extension Service recommends the following herbicides for controlling specific weeds listed:

Sandbur, grassbur, spur weed, cocklebur – pre-emergent, apply by March 1; Brands – PreM by Lesco; Amaze Grass & Weed Preventor by Green Light; Surflan, A.S. by Southern Ag.; Weed & Grass Preventor by Lilly Miller; weed Stopper by Lawn & Garden Products.

Virginia Button weed – Post emergent in St. Augustine grass lawns, such as dicamba (Banvel) or products containing dicamba (Trimec) provides some control with two or more applications in spring and summer.

Crabgrass – germinates April- October in many areas, note few of these herbicides provide season-long control. DCPA (Dacthal), simazine (Princep), besulide (Betasan, Pre-san), benefin (Balan), dithiopyr (Dimension), oxadiazon (Ronstar), oryzalin (Surflan), prodiamine (Barricade), pendimethalin (Pre-M) and napropamide (Devrinol) are some of the materials available for preemergent crabgrass control.

Chickweed – Spray preemergent herbicides such as simazine, dithiopyr, dacthal, oryzalin, pendimethalin and isoxaben in fall.

Henbit – Dicamba, MCPP and 2,4-D provide effective control in the fall and early spring.

Yellow Sorrel – Apply preemergent herbicides such as dacthal, oryzalin (Surflan), pendimethalin (Pre-M), isoxaben (Gallery), dithiopyr (Dimension) and oxadiazon (Ronstar) in early spring.

Prostrate or Spotted Spurge – Dacthal, pendimethalin and Surflan provide preemergent control of spurge in warm season turfgrasses. Apply in early spring to be effective, 2nd application is necessary 60 days from initial application.

Quack & Torpedo grass – Sadly, there is but one herbicide which works on this weed, glyphosate. Personal safety is critical before attempting use. Wear gloves, a long-sleeved shirt and don a face mask (respirator) when using this product. Paint weeds with a brush to keep from damaging nearby plants.

Nutsedge or nutgrass – preemergent herbicide metolachlor (Pennant) is labeled for the control of yellow nutsedge (nutgrass). For post-emergent control of sedge, the herbicide imazaquin (Image) is labeled for purple and yellow nutsedge.

Chamber bitter weed – preemergent herbicides with atrazine applied in the early spring prior to germination. Post emergent herbicides also with atrazine are effective when applied to young weeds.

There are plenty more weeds that could be listed, but these are commonly found in SETX. Follow along for next week’s final installment, winter lawn care. So long for now fellow gardeners, let’s go out and enjoy Shangri La Botanical Gardens Annual Scare Crow Festival. Visit shangrilagardens.org for more information. Hope to see you there!

Send comments and questions to Texas Certified Master Gardener John Green at jongreene57gmail.com.