Turfgrass Management and Weed Control (Part 2 of 3)

What a fantastic week, the temperature is finally moderating as autumn-like weather is slowly sneaking into our area! Now, let’s hope we get increased rain chances in the weather forecast, as I’m certain all of you (myself included) are watering lawns, vegetable beds and flower gardens once or twice weekly. The cooler morning temperatures are making garden work a much more pleasant experience, which means spending more time outdoors. Stay hydrated and wear sun protection. Last week I discussed basic weed grouping: annuals, biennials, and perennials and Turfgrass. Now that weed types have been reviewed, let’s discuss how to go about controlling them. Weed control can be achieved utilizing multiple methods. One way is to manually dig each one up individually, which if there are only a few in your landscape, a good choice. For large areas teeming with weeds, and without Turfgrass, the area can be covered with heavy plastic or a tarp for about 4 weeks, using the suns energy to destroy the weeds. Another method is by using pre- and post- emergent herbicides, in either organic or chemical forms. So, let’s discuss the different groups of herbicides in greater detail, breaking down each group for better a understanding of exactly to apply them and how they work.

Pre-emergent herbicides are applied before weeds sprout through the soil surface. To control warm-season annual weeds, apply a pre-emergent herbicide in early spring. For us in the southeast TX area, January thru March is best, before the soil temperature reaches 55 degrees F. For weeds which sprout sprout later in the summer, a second application will be required in June or July. For cool-season annual weeds, apply August to September. Naturally, this will vary year-to-year, depending on our temperatures.

Post-emergent herbicides are applied after weeds have sprouted. They are most effective when weeds are still small, less than 4 inches high.

Contact Herbicides cause damage wherever they touch a plant. To work well they must cover all parts of the leaves and stems, including the top and undersides of leaves.

Systemic Herbicides are absorbed on a cellular level and moved throughout the plant. They are applied to the soil around the base of the plant, to the plant itself or both. They are moved thru the plant from foliage to roots, stems and other plant parts. They work extremely 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, normally at 6-to-8-week intervals, especially on weeds which are more difficult to control.

Selective herbicides will kill one type of plant but not others, like your turf grasses. Nonselective herbicides will kill almost any plant they touch, you’ll want to be extremely careful when using these types of herbicides!

As with all herbicides, read before spraying. It is imperative to always read the directions for application, ensuring the product you plan on use will eradicate or control the specific weed(s).

For specific types of weeds, Texas A&M AgriLife Extension Service recommends the following:

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. If some discoloration of St. Augustine grass can be tolerated, Confront at 2 pints per acre and Scotts DMC at 1 ounce per acre have will provide good control of button weed.

Crabgrass - A few herbicides have been developed for turf because of that research, 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. Crabgrass germinates from April through September in most areas of the country (slightly shorter periods in other areas). Note: few of these herbicides provide season-long control.

Dandelion – spray 2,4-D in spring before blooms set

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

Henbit - Dicamba, MCPP and 2,4-D have demonstrated effective control in the fall and early spring

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

Prostrate or Spotted Spurge – Dacthal, pendimethalin and Surflan have provided good preemergent control of spurge in warm season turfgrasses. They must be applied in early spring to be effective, with a second application necessary 60 days after the initial application. 

Quack & Torpedo grass – Unfortunately, the only herbicide which works well on this weed is glyphosate. Wear gloves, long-sleeves and mask when using and paint weed with brush to keep from damaging nearby plants. You can also dig the plant out ensuring to dig deeply enough to get all the roots.

Nutsedge or nutgrass - preemergent herbicide metolachlor (Pennant) is labeled for the control of yellow nutsedge (commonly known as nutgrass) in ornamental beds. 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. Seeds need light to germinate, mulching with 3-4 inches in garden beds will help.

There are many more weeds which could be listed, but these are the most common found in our area. Next week, part 3, we will review Winter lawn management. Now my fellow gardeners, let’s go out and grow ourselves a greener, more sustainable world, one plant, at a time!

If you have specific gardening questions or would like more information, contact the Orange County Master Gardeners Helpline: (409) 882-7010 or visit our website: https://txmg.org/orange, Facebook: Orange County Texas Master Gardeners Association or Email: [email protected].