What Kills Crabgrass in St. Augustine Grass?

Crabgrass – the scourge of many a beautiful St. Augustine lawn. As a long-time gardener and lawn care enthusiast, I know firsthand how frustrating crabgrass infestations can be. Those unsightly clumps of grassy weeds seem to pop up overnight, marring the lush green carpet of your prized St. Augustine turf.

While crabgrass can certainly be a headache, don’t give up hope! With the right strategies and products, it is possible to knock out crabgrass and reclaim your gorgeous lawn. In this article, I’ll share my proven crabgrass control methods that I’ve successfully used in my own St. Augustine grass over the years.

You’ll learn all about the tricky life cycle of crabgrass, how it spreads, and when it’s most vulnerable to pre and post-emergent treatments. I’ll also provide specific product recommendations, including natural and organic options, that will effectively eliminate crabgrass without harming your treasured St. Augustine. Whether you want to prevent crabgrass before it sprouts or remove existing weeds, you’ll find the solutions here.

By the end, you’ll have the confidence and know-how to finally show stubborn crabgrass the door. Bid farewell to those unwelcome clumps for good, and welcome back a lush, verdant lawn you can be proud of. Now, let’s get busy and banish crabgrass for good!

How Does Crabgrass Infest St. Augustine Lawns?

As an experienced gardener, I’ve seen firsthand how troublesome crabgrass can be for St. Augustine grass. To gain the upper hand over this stubborn invader, it’s important to understand exactly how crabgrass infests our lawns in the first place.

Crabgrass relies on two key strategies to infiltrate and spread throughout St. Augustine turf. First, it produces an abundance of seeds that can lie dormant, waiting for the right growing conditions. Second, it is an opportunistic plant that flourishes during the hot summer months when St. Augustine is vulnerable.

The Tricky Crabgrass Life Cycle

Crabgrass has a tricky annual life cycle that helps it evade many control efforts. Each mature crabgrass plant can produce up to 150,000 seeds that fall to the ground. These hardy seeds can remain viable for up to six years in the soil, patiently waiting for their chance to sprout.

Once temperatures reach 55-60°F in spring, crabgrass seeds begin germinating. The young crabgrass seedlings thrive when temperatures climb above 65°F coupled with ample moisture. During summer’s heat, crabgrass grows rapidly, producing new plants via stems that root at the joints. By fall, it sets seed and dies after the first hard frost. The cycle then repeats again the following spring.

Crabgrass Spreads Through Difficult-to-Control Seeds

The prolific nature of crabgrass seeds makes this weed difficult to control. Weed preventer products aimed at stopping seeds from germinating must be applied early in spring before soil temperatures reach 55°F. Timing is key, as soil temperature dictates crabgrass germination. Reapplication may be needed for full season control since pre-emergents lose potency over time.

For existing weeds, post-emergent crabgrass killers containing active ingredients like quinclorac or MSMA are options. However, results vary depending on timing and product used. Persistent follow-up applications are usually needed to fully eradicate established crabgrass plants.

Crabgrass Thrives in Thin, Bare Soil

Crabgrass in St. Augustine Grass

Crabgrass invades thin, sparse lawns where it finds plenty of bare spots to put down roots. St. Augustine grass is prone to thinning when the soil dries out, heat intensity ramps up, or following disease and insect damage. Crabgrass seeds waiting in the wings take advantage and quickly occupy the real estate.

Proper mowing, irrigation, fertilization and other care practices strengthen St. Augustine grass, allowing it to maintain a dense, thick lawn. This competitive edge helps choke out crabgrass seeds trying to germinate. Keeping your lawn vigorous and healthy is key to preventing colonization by opportunistic crabgrass invaders.

While crabgrass employs some clever strategies, you now know exactly how it sneaks into St. Augustine lawns. Armed with this insight, you can more effectively plan your crabgrass control timing and techniques. By disrupting its life cycle and growth habits, you can conquer this stubborn weed.

When to Treat Crabgrass in St. Augustine Grass?

Timing is everything when it comes to effective crabgrass control in St. Augustine lawns. To successfully break the cycle of this wily annual weed, you need to hit it at its most vulnerable stages.

Crabgrass prevention and control programs utilize specially timed herbicide applications – both pre and post-emergent products – that disrupt crabgrass at key points in its life cycle. Here’s an overview of when to deploy the various treatment options for season-long control.

Spring Application of Pre-Emergent Herbicide

As a lawn care pro, my number one recommendation is applying a pre-emergent herbicide in early spring. This protective barrier stops crabgrass seeds from germinating and developing into mature plants.

Timing is critical – soil temperature must reach 55-60°F before crabgrass seeds start germinating. Where I live, I’ve found that the optimal window is mid-March to early April. Reapplication may be needed 8-10 weeks later if the product’s potency diminishes before summer’s end.

Correct timing and application of pre-emergent is key to preventing a full-blown crabgrass infestation. Used properly, it can eliminate the need for post-emergent control later.

Early Summer Post-Emergent Treatment

If crabgrass manages to sneak through your pre-emergent barrier, post-emergent herbicides can knock it out early in the summer. The younger the plants are, the more effective control will be.

Small, 1-3 inch crabgrass plants are most susceptible. Target them in early to mid-June before they become large and difficult to kill. For mature plants over 3 inches tall, repeated applications are usually required. Go after escapee plants promptly or they’ll continue spreading.

Second Application in Mid to Late Summer

In warmer climates or if your pre-emergent potency declined, a second application in August may be warranted to prevent late summer and fall crabgrass emergence. Keep an eye out for new seedlings and treat as needed.

Killing existing crabgrass before it goes to seed will help reduce the soil seed bank over time. Doing so by early September is ideal to prevent a flush of new growth once cooler temperatures arrive.

Consistent timing of pre and post-emergent control measures disrupts the crabgrass life cycle at key stages. By deploying products at optimal points early and late in the growing season, you can break the cycle and tip the scales against this powerful invader. Give crabgrass the one-two punch for clean knockout!

Effective Crabgrass Killers for St. Augustine Grass

When crabgrass rears its ugly head in St. Augustine lawns, you need proven products to gain control. As a longtime gardening expert, I’ve tested an array of pre and post-emergent herbicides over the years and discovered which ones deliver the best bang for your buck.

The key is using EPA approved products labeled for use on St. Augustine grass. Always carefully follow label directions to avoid potential turf damage while getting maximum weed control. Here are my top recommended options:

Pre-Emergent Crabgrass Preventers

Pre-emergent herbicides create a barrier that stops crabgrass seeds from germinating. Two of the most effective active ingredients to look for are prodiamine and dithiopyr.

Prodiamine products, such as Barricade, inhibit root development in newly germinating crabgrass. Apply before soil temperatures reach 55°F and water in well after application. For season-long control, plan on a follow-up application 8-10 weeks later.

Dithiopyr, found in Dimension, offers contact and residual activity. It not only prevents new seeds from sprouting, but also controls young crabgrass up to the 3-4 leaf stage. Apply around early to mid-April and again in June if needed.

Using a combination product with both active ingredients, such as Echelon, enhances performance. Just be sure to time applications correctly for optimal results.

Post-Emergent Crabgrass Killers

Once crabgrass emerges, post-emergent herbicides take it out. Quinclorac, the active ingredient in products like Drive XLR8, is one of the best. It’s absorbed quickly by crabgrass leaves and translocated to the roots. Two applications 7-10 days apart provide complete control.

For larger mature crabgrass, MSMA products like Crabgrass Killer work well. Apply during summer when crabgrass is actively growing for best results. Re-treatment will likely be needed. Take proper safety precautions.

For spot treating sparse areas, a ready-to-use formula like Ortho Weed B Gon for St. Augustine grass is very effective. Look for quick visual results in as little as 24 hours.

Natural and Organic Crabgrass Treatments

For those seeking non-chemical options, corn gluten meal and vinegar can provide moderate control when properly applied. Just know results take longer and more applications may be required. Still, they are viable natural alternatives.

The right herbicides coupled with perfect timing provide the knockout 1-2 punch required to rid St. Augustine lawns of unsightly crabgrass for good. Always be sure to carefully follow label instructions to ensure both effective weed control and healthy grass. Your lawn will be crabgrass free in no time!

FAQ: Controlling Crabgrass in St. Augustine Lawns

When battling a crabgrass infestation, you’re likely to have lots of questions. Here I’ll address some of the most common FAQs I receive about getting rid of crabgrass in St. Augustine grass lawns.

What is the best pre-emergent for crabgrass in St. Augustine?

Based on my experience, I highly recommend using a pre-emergent herbicide containing prodiamine or dithiopyr. Both active ingredients are safe for St. Augustine grass when applied at the right time.

Prodiamine products like Barricade do a great job preventing crabgrass seeds from sprouting. Dithiopyr formulas such as Dimension offer both pre and early post-emergent control. Using them together provides even better protection.

No matter which active ingredient you choose, proper timing is key. Apply in early spring before soil temperatures reach 55°F, when crabgrass seeds start germinating. Reapply 8-10 weeks later if needed.

How do I get rid of crabgrass without killing St. Augustine grass?

The good news is there are several effective options for selectively removing crabgrass from St. Augustine lawns. Quinclorac is one of the best post-emergent active ingredients for crabgrass control in warm season grasses. Products containing MSMA or ammonium nonanoate also work well.

Spot treating young crabgrass invaders with a ready-to-use formula like Ortho Weed B Gon or Bonide Weed Beater is also highly effective. Just take care not to over apply. Remove larger mature plants manually if possible before seeds develop.

Proper timing and application are key for avoiding turf damage while eliminating existing crabgrass plants. Follow label directions carefully when using any herbicide.

When should I put down crabgrass preventer in St. Augustine?

To stop crabgrass before it even sprouts, your best bet is applying pre-emergent herbicide in early to mid-spring. I recommend split applications 8-10 weeks apart for season-long control.

Here in zone 8, I target the first week of April for an initial application, followed by a second round in early June. But timing varies by region, so it’s critical to treat before soil temperatures exceed 55°F.

Getting your pre-emergent down at just the right time is crucial for effective crabgrass prevention in St. Augustine lawns. Your local extension can provide timing recommendations specific to your area.

Arm yourself with the right intel and products to take down crabgrass in St. Augustine grass. A little planning and strategic timing is all it takes to gain the upper hand. With persistence, you can reclaim a lush, verdant lawn free of crabgrass woes.

Conclusion and Recap

Dealing with a crabgrass invasion in your prized St. Augustine lawn can feel like an uphill battle. But with the right timing and tools, it is possible to gain the upper hand against this stubborn summer weed.

This guide has equipped you with in-depth knowledge of how crabgrass operates, along with expert tips for targeting it at its weakest points. By disrupting the crabgrass lifecycle through properly timed pre and post-emergent herbicide applications, you can break its ability to spread.

Your lawn will rebound with a thick, verdant carpet of lush St. Augustine grass once cramping crabgrass plants are eliminated. Just be vigilant about reapplying treatments as needed throughout the growing season for full control.

With persistence and dedication to early spring and summer application timing, you can safely knock out existing crabgrass while preventing future outbreaks. Soon, you’ll be able to reclaim those bare spots and say goodbye to crabgrass for good.

As a fellow lawn care enthusiast, I know how satisfying it is to successfully banish crabgrass and see your St. Augustine thrive again. So roll up your sleeves, get ready to do battle, and soon you’ll be victorious over the crabgrass monster! Your healthy, beautiful lawn awaits.

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