Guide To Weed Control For Warm Season Grasses

If you live in the South, you are probably more familiar with the climate. The summers are long and scorching hot and humid, while the winters are mild and much shorter than the rest of the country.

Warm-season grasses are more tropical and thrive in the summer when the temperatures are high (between 80 and 90 degrees Fahrenheit). One of the traits of warm-season grasses is the thick and dense lawn cover, which remains green all summer long and will begin to brown in the wintertime. The grass greens up again when it begins to get warmer. In general, they are green a little over half the year.

The most common warm-season southern grasses are Centipede, St. Augustine, Bermuda, and Zoysia. Each has its own traits and maintenance needs so it can stay healthy and bright. But like most lawns, undesirable weeds can creep up and ruin the uniform look of your turf.

In this guide, we will look at how to manage weeds on warm-season grasses using proper cultural practices and the help of herbicides, which will keep your warm-season grasses healthy and weed-free all year.

Identification

The first step in tackling invasive weed species is proper identification. Since mowing the lawn removes flowers and seedheads, it can often be tough to identify your weeds unless you let them grow and get a good idea of what weed is present. Below, we have compiled a list of more common weeds on warm-season grass.

Chamberbitter

Also known as gripe weed, Chamberbitter is a small summer annual once sought after ornamentally. Since then, it has become an invading weed that has gotten out of control on lawns. Chamberbitter is heavily branched at the base with ascending stems, often forming a mound 1 to 2 feet in height.

Doveweed

Doveweed is a summer annual that grows best in moist, sunny areas and first germinates in late spring. It looks similar to St. Augustine or centipede grass. It has linear leaves that can be up to four inches long, with soft hairs on the sheaths and a rubbery texture. Doveweed grows clusters of pale purple flowers throughout the summer, and its stems root at the nodes, allowing them to spread by stem fragments.

Sandspur

Also known as burweed, sandspur is a low-growing winter-annual broadleaf weed with narrowly separated leaves and small noticeable flowers. It is perhaps most known for its small spiky stickers, which can prick skin when walked with bare feet over them.

Dollarweed

Dollarweed is a moisture-loving perennial warm-season weed that is recognized by its round, lily pad-like leaves and five-petaled flowers that resemble stars.

Virginia Buttonweed

Virginia buttonweed is known for forming thick mats that spread and are deeply rooted in the soil. Its branched stems are covered in little hairs, and it grows white four-petaled flowers that are also hairy. Virginia buttonweed can spread and generate in various ways, making it particularly frustrating.

Wild Garlic/Onion

Wild garlic and wild onion are perennial weeds similar in that they have hollow, stem-like leaves. They get their name from the bulbs they form, which resemble onions and give off a strong garlicky smell.

Inspection

It is important to thoroughly inspect your lawn when you notice weeds and invasive plants emerging. An inspection will help determine what weeds are on your property so you know where they are concentrated, what conditions may be helping them thrive, and what herbicides may best control them.

Where to Inspect

Scan your lawn and look for the weeds we described in the identification section. The best time to inspect your lawn for weeds is in the early fall (October or November) for winter weed control, and then follow up again with an inspection in early spring (March or April). Inspecting in the early part of fall is best because there is a chance of early detection and subsequent treatment since weeds are most vulnerable to herbicide treatment when they are young.

What to Look for

Closely observe the traits of the invading weeds and determine what species they are. It would be best to look at the surrounding environment for anything that can explain why the weed is thriving. Is the soil compacted? Are there drainage issues? Is your grass undergoing a lot of stress? Finding these answers can determine how you approach control.

Treatment

Once you have pinpointed and properly identified the weeds on your warm-season lawn, the next step is to control them with herbicides. There are two types of herbicides: post-emergent and pre-emergent.

Pre-emergent herbicides are a preventative measure used when you know about a particular weed that grows at a certain time every year and lay out a pre-emergent to prevent the weed from germinating.

Post-emergence herbicides are weed killers that kill visible weeds that have already sprung up. Young weeds in the two—to four-leaf stage and those actively growing are the most vulnerable to herbicide chemicals and require the least amount of herbicide to control them successfully.

The timing of the application is essential for the best results. During this early stage, herbicide uptake and translocation take place more easily, and weeds have weaker root systems to provide much resistance. Suppose you wait until plants have grown more mature. In that case, there will be a significant dip in the herbicide translocation, making it tougher to control mature weeds and raising the chances of injuring your grass if higher rates are needed to achieve weed control.

Thus, post-emergence herbicides should only be used when weeds are in active growth. This primarily occurs when temperatures are between 40 and 80 degrees, and good soil moisture is available. Applying herbicides outside of this temperature range or when soil is on the dry side will result in the herbicide performing slowly and can lead to turf damage from excessive herbicide use.

Pre-Emergents For Warm Season Weed Control

Our top recommendation for pre-emergent control of most warm-season weeds is Prodiamine WDG. Prodiamine works by stunting the development of seeds at the beginning of the germination phase. It is labeled for most grasses, but it may be harmful to Annual Bluegrass, so if that is a desired grass on your lawn, use it with caution.

Calculate the square footage of your yard to determine how much Prodiamine you will need.

The maximum application rate can range anywhere from 0.185 oz. to 0.83 oz. of Prodiamine WDG per 1,000 sq. ft. per calendar year.

Mix the appropriate measured amount with water based on your calculations and apply over your entire lawn uniformly.

Pre-emergent herbicides should be applied in the fall. Most warm-season turfs go dormant when winter arrives, and temperatures drop, and an application of pre-emergent will protect the turf from weeds that may appear in the winter.

Post-Emergents For Warm Season Weed Control

Our top recommendation for controlling post-emergence broadleaf and grassy weeds in warm-season turfgrasses is 2,4-D Selective weed killer. This is a selective herbicide, meaning it will only harm target weeds and spare desired warm-season grasses.

For small applications with a hand sprayer, mix between 0.72 to 1.1 fl. oz. in a gallon of water to treat 1,000 square feet.

Fill your sprayer halfway with water, add the appropriate measured amount of 2,4-D, and then fill the rest with water. Apply the 2,4-D mixture to areas where unwanted vegetation grows, preferably on a fan spray setting, to ensure even coverage.

Once again, control depends upon how mature the weed you are targeting is. Younger weeds are the easiest and cheapest to control. To tackle winter annuals, applications should be started in November to take advantage of these younger, more succulent plants.

Waiting until March or April to attempt control may result in the need to do multiple follow-up applications every 10 days or two weeks, resulting in a lot of herbicides being lost, which can be costly. Applying herbicides late may also affect your warm-season grass, hindering its ability to green up and making it work slower to get the results you seek. For summer-annual weeds, mid- to late-spring applications are recommended.

Prevention

To successfully prevent future weeds on your warm-season lawn, you will need to combine good cultural practices and the right herbicides to create a thick, healthy turf that will tackle the weeds and give your warm-season grass the advantage of keeping them from thriving.

Dethatch your lawn in May when your grass is actively growing by raking it regularly. This promotes a healthy lawn by removing dead roots and stolons that may be stuck between the soil surface and your living turf, encouraging better grass growth.

Trim back tree branches to reduce shade and promote proper water retention in your soil. Water your grass 1 to 1.5 inches a week, and mow it 3 to 4 inches taller to encourage root growth.

Finally, ensure you fertilize your lawn with the proper amount of Nitrogen it needs so it is equipped with the nutrition necessary to fight against invasive weed threats.

Key Takeaways

• Warm-season grasses like St. Augustine and Zoysiagrass thrive in warmer climates in the Southern United States. Common invasive weeds include dollarweed, spurge, clover, and sandspurs.
• We recommend Prodiamine 65 WDG for pre-emergent control of most warm-season weeds and 2,4-D Amine Selective Weed Killer for post-emergent control.
• Implement lawn maintenance practices like regular mowing, watering, and dethatching that promote thick, dense turf. Thick turf will minimize the opportunity for weeds to thrive in your yard, preventing future weed problems.