Crabgrass is a warm-season annual grassy weed that aggressively invades lawns during the summer months. While it dies off with the first frost, an infestation raises the question of whether effective summer treatment is possible. Summer removal is absolutely possible, but it requires a strategic shift from the prevention methods used earlier in the season. Eliminating this weed during the growing season depends entirely on employing specific, post-emergence control techniques.
Why Summer Removal Requires a Different Approach
Controlling crabgrass in the summer is more complicated because the plant has reached maturity and the surrounding turfgrass is under stress. By summer, the plants are large and fully established, having developed multiple tillers. These side shoots create a dense, sprawling mat, making mature plants far more resilient to herbicides than young seedlings.
The plant’s maturity also means it is actively producing seed heads, which can remain dormant in the soil for future years. Crabgrass thrives in high temperatures, while most desirable cool-season turfgrasses, like fescue and bluegrass, experience a slowdown in growth. This summer dormancy makes the turfgrass highly susceptible to injury from chemical treatments, necessitating careful application timing to protect the lawn.
Chemical Strategies for Mature Crabgrass
When dealing with a substantial summer infestation, chemical control through selective post-emergent herbicides is necessary. These products are designed to kill the weed without harming the surrounding turf, provided they are specific to your grass type and the crabgrass’s growth stage.
Quinclorac is a common and effective post-emergent herbicide that controls mature crabgrass, even plants with multiple tillers. This ingredient is generally safe for established cool-season turfgrasses and works systemically by being absorbed through the leaves. Fenoxaprop-p-ethyl is another effective option that provides excellent control at all growth stages of the weed, though it may cause temporary injury to certain varieties of Kentucky bluegrass when applied during peak heat.
For optimal results, these herbicides should be applied with an adjuvant, such as a methylated seed oil or crop oil concentrate, to help the chemical penetrate the waxy leaf surface. Avoid applying herbicides when temperatures exceed 85 degrees Fahrenheit or during the hottest part of the day, as this can severely burn the lawn. Spot-treating individual crabgrass patches rather than blanket spraying the entire lawn helps minimize stress on the surrounding grass.
Non-Chemical and Cultural Control Methods
For smaller, localized summer infestations, non-chemical methods offer control without exposing the stressed lawn to herbicides. Manual removal is the most direct approach for small patches, but it is important to remove the entire root crown to prevent regrowth. Watering the area lightly before pulling can loosen the soil, making it easier to extract the shallow roots completely.
Cultural practices that favor the growth of turfgrass are also part of an effective summer control strategy. Raising your mower height to at least three inches shades the soil, keeping it cooler and making conditions less favorable for crabgrass to thrive.
Adjust your watering schedule to deep, infrequent irrigation, aiming for one to one-and-a-half inches of water per week. This encourages the turfgrass to develop deep, strong roots while denying the shallow-rooted crabgrass the frequent surface moisture it needs. Avoid applying nitrogen-heavy fertilizers in the summer, as crabgrass will utilize the nutrients more efficiently than cool-season turf, inadvertently fueling the weed’s growth.
Planning for Next Season’s Prevention
While summer treatments address the immediate problem, a long-term solution requires focusing on next season’s prevention, as seeds can remain viable in the soil for years. The most effective preventative measure is applying a pre-emergent herbicide in late winter or early spring. This chemical forms a barrier near the soil surface that stops weed seeds from establishing roots when they germinate.
The timing of this application is governed by soil temperature, not the calendar date. Pre-emergent must be applied before the soil temperature at a two-inch depth consistently reaches 55 degrees Fahrenheit for three to five consecutive days. Using a soil thermometer or local extension resources to track this temperature is the most accurate way to time your application.