Johnsongrass Invasion: How to Treat This Aggressive Grass Weed in Texas

If you’ve got tall, coarse grass with wide leaves and reddish-purple seed heads growing in your lawn, along your fence line, or invading your landscape beds, you’re dealing with Johnsongrass—one of the most aggressive and difficult-to-eradicate grass weeds in all of Texas. Listed as a noxious weed in many states, Johnsongrass can reach six feet tall, spreads through both seed and an extensive underground rhizome network, and is capable of completely overtaking thin or unmanaged turf. Here’s what you’re actually dealing with and how to fight it effectively in North Texas conditions.

What Is Johnsongrass?

Johnsongrass (Sorghum halepense) is a perennial grass weed in the sorghum family, originally introduced to the United States as a forage crop in the 1800s. It quickly escaped cultivation and is now considered one of the worst agricultural weeds in the world. In Texas, it’s everywhere—roadsides, pastures, crop fields, vacant lots, and residential lawns. It’s especially problematic in DFW where the clay soils hold moisture and the warm climate lets it grow aggressively from April through October.

Key identification features:

• Leaves are wide (up to an inch), coarse, and have a distinctive white midrib running down the center
• Plant is tall—mature plants reach 3–6 feet in a single season
• Seed head is a large, open, branching panicle with reddish-purple seeds
• Underground rhizomes (horizontal root-like stems) that are white, jointed, and can extend several feet from the parent plant

Why Johnsongrass Is So Hard To Kill

Johnsongrass is difficult to control for several compounding reasons:

• Dual reproduction: It spreads by seed—producing thousands of seeds per plant—AND by rhizomes that sprout new plants several feet away from the original. Kill the visible plant and the rhizome system pushes up new shoots within weeks.
• Deep rhizome network: The rhizomes can penetrate 12 inches or more into the soil, storing energy reserves that fuel regrowth after herbicide treatment. A single treatment rarely delivers enough systemic herbicide to the entire root system to prevent recovery.
• Resistance to standard broadleaf herbicides: Since Johnsongrass is a grass, the 2,4-D and dicamba products that kill broadleaf weeds have zero effect on it. You need grass-selective chemistry, and in a Bermuda or other grass lawn that creates a real challenge.
• Fast growth: In DFW summers, Johnsongrass can grow several inches per week. Miss a mowing cycle or a treatment window and you’re back to full regrowth.

The Challenge in Grass Lawns

This is the core problem with Johnsongrass control in residential turf: the best herbicides for Johnsongrass are grass-selective, meaning they also kill or damage the desirable lawn grass. In non-turf areas—landscape beds, fence lines, vacant areas—glyphosate (Roundup) or fluazifop are highly effective. In a Bermuda or St. Augustine lawn, those same products will damage or kill the turf.

In Bermuda grass, the situation is slightly more workable: products containing fluazifop or sethoxydim have some selectivity in Bermuda at lower rates, though results vary and turf damage is possible. Most turf professionals take a targeted spot-treatment approach rather than broadcast application—applying carefully to the weed and immediately surrounding area rather than the full lawn. In St. Augustine, the options are even more limited, and removal often comes down to physical removal plus repeated digging and spot treatment with glyphosate on regrowth.

Effective Control Strategies

Professional weed control for Johnsongrass requires a multi-season commitment and strategic approach:

• Repeated spot treatments with systemic herbicides: In non-turf areas, glyphosate applied to actively growing plants in summer and fall is highly effective when repeated. Each treatment weakens the rhizome system further. Expect 3–4 treatments over two seasons to achieve substantial control.
• Prevent seed production: Mow or treat plants before they flower and set seed. Reducing seed input slows the expansion of the infestation significantly over time.
• Physical removal in small areas: Digging out rhizomes in landscape beds is labor-intensive but effective when done thoroughly. Every rhizome piece left behind can regenerate, so it must be comprehensive.
• Pre-emergent for seedling control: Pre-emergent herbicides prevent Johnsongrass seedlings from establishing but don’t affect established rhizomes. They’re a useful part of the program to reduce new seedling recruitment while you tackle existing plants.
• Building competitive turf: Where Johnsongrass is invading thin lawn areas, thickening the turf through fertilization and overseeding reduces the open gaps that allow seedling establishment.

Realistic Timeline for Control

Established Johnsongrass with a developed rhizome system typically requires two to three full growing seasons of consistent treatment to bring under control. First season reduces top growth and weakens rhizomes. Second season is where you see major decline. Third season is maintenance. Homeowners who give up after one treatment—when the weed regrows from rhizomes—never get ahead of it. Consistency is everything.

DFW-Specific Timing

In North Texas, Johnsongrass emerges in late March and April and grows aggressively through October. Treatment timing for maximum effectiveness:

• Early season (April–May): First treatment when plants are young and most susceptible to systemic herbicides
• Midsummer (July–August): Follow-up treatments on regrowth from rhizomes
• Fall (September–October): A late-season treatment when plants are translocating nutrients to rhizomes delivers exceptional systemic uptake to the root system

Hamann Tackles Johnsongrass Across DFW

Hamann Lawn Care & Weed Control has been battling aggressive grass weeds like Johnsongrass in Arlington and throughout the DFW metroplex since 2006. We know which products are appropriate for each situation and turf type, how to minimize turf damage during treatment, and how to build a multi-season plan that progressively eliminates the rhizome network. For a close relative that causes similar frustration in DFW lawns, read our post on sandbur and grassbur control—another grass weed that requires persistent pre-emergent timing and professional chemistry to beat.

Johnsongrass is not a weed you beat in a weekend. But with the right program and a multi-season commitment, it can absolutely be brought under control. Call us and let’s build a plan for your specific situation.