Controlling Post-Emergent Crabgrass

Thanks to its swift growth, hardiness, and prolific seed production, crabgrass (Digitaria) plagues landscapes everywhere. According to the Michigan State University Extension, the best defense against crabgrass invasion is to maintain a dense, healthy turf stand by mowing at the proper height and fertilizing.

But crabgrass is notoriously tough. From mid-summer till early fall, crabgrass plants produce thousands of seeds. While frosts kill the plants, the seeds stay dormant through the winter, and when the ground temperature warms up, those seeds wake up and grow. So, the goal is to ensure those seeds can’t germinate.

Pre-emergent Strategy

Ideally, when you want to preserve the health and aesthetics of your clients’ lawns and landscapes, you should catch crabgrass before it shows up.

Timing is key. Crabgrass begins to germinate when soil temperatures reach 55-60°F (13-16°C) for 4-5 consecutive days, usually in late spring or early summer. Staying alert to local weather patterns and soil temperatures can help you time your crabgrass control applications accurately.

If possible, plan the application of pre-emergent herbicides when soil is around 50°F, so it’s in place when the crabgrass begins to germinate. 4-6 weeks later, a reapplication of pre-emergent makes sense to catch newly emerging crabgrass before it can get a foothold.

Again, it’s all about timing. Apply pre-emergent herbicides too late, and crabgrass will germinate and start growing before the herbicide is settled into the soil. Apply it too early, and potency is depleted before the crabgrass seeds have germinated.

For a broad array of pre-emergent herbicides, you can search through the herbicides section of our website here.

Once crabgrass has arrived, however, pre-emergents will no longer be effective, but you still have plenty of options.

Post-Emergent Strategy

Postemergence control of crabgrass—and other annual summer grass weeds—means using products that control growing crabgrass and its relations after they’ve already shown up in your customer’s turf.

Prepping the Lawn: it’s crucial to properly prepare lawns before you apply post-emergent crabgrass herbicides. Mow the grass to the recommended height for the turf type in question.

Make sure it’s been liberally watered for several days before applying the post-emergent herbicide. When a lawn is healthy and well maintained, it will hold up to herbicide treatments, and more quickly recover.

Post-emergence herbicides are exactly that: they are to be applied at any point after crabgrass has germinated. While there are several post-emergence herbicides designed for controlling crabgrass, because these “post-emergents” may only apply to one or two turf species, make sure the one you choose is labeled for the turf type and use area where you plan to apply it.

These herbicides usually provide better control when applied to small actively growing crabgrass plants—i.e., less than two tillers (a tiller is a shoot rising from the base of a grass plant).

With larger plants (three-plus tillers), multiple applications spaced two to three weeks apart are usually necessary for complete control. Once plants grow too large (typically by mid-July), they are much tougher to eradicate.

Tips for Effective Post-Emergent Herbicide Application:

1. For maximum effectiveness, unwanted grasses must be uniformly covered (i.e., herbicides should be applied only when annual grasses are visible in the stand).
2. Applicators should pay close attention to product label directions, and factor in the target species, the given weed’s stage of growth and corresponding herbicide rate, to ensure successful crabgrass control.
3. Because environmental conditions are crucial to controlling post-emergent grasses, ensure adequate soil moisture and moderate temperatures to get the best results.
4. Ideal temperature for herbicide application is 60-90°F, though if your turf is stressed from too-dry or drought conditions, or temps are higher, plants can absorb the herbicide too quickly. Too-cool temps or cloudy conditions can reduce the product’s effectiveness.
5. Use LESCO Spreaders and LESCO Sprayers for best results.
6. A suddenly-browning lawn can mean you may have applied too much herbicide. If this happens, water the lawn immediately to dilute the herbicide.
7. After herbicide treatment, keep an eye out for newly sprouted crabgrass plants and spot-treat them with herbicide.
8. Add a spray adjuvant to postemergence herbicides for optimal crabgrass control.
9. As always, read product labels carefully for proper-use instructions.

LESCO Products for Crabgrass

Herbicides with the active ingredient Quinclorac (options below) are effective for post-emergent control of crabgrass, foxtail, barnyard grass, and several broadleaf weed species in established turfgrass. It controls newly emerged summer annual grasses, along with mature plants (i.e., annual grasses with more than 4 tillers).

For a broad array of post-emergent herbicides, visit the herbicides section of our website here.

1. LESCO Quin-Way
2. LESCO Momentum-Q: Containing active ingredients quinclorac, 2-4-D and dicamba, the product controls over 200 species of broadleaf weeds, including tough species like foxtail, barnyard grass and signalgrass.
3. Herbicides with the active ingredient Mesotrione are also effective at controlling crabgrass. Products containing Mesotrione such as Tenacity and Meso 4SC can purchased at SiteOne.

For a broad array of post-emergent herbicides, visit the herbicides section of our website here.

And remember, local SiteOne branch associates are available to help answer questions and are ready to serve all lines of business needs. For more information on all our offerings, shop our website or download our mobile app.