I hear from listeners who have been disappointed with pre-emergent herbicides like Barricade and Dimension – the two most readily available on the market today.
Some say they have more weeds than ever and are bummed because the products didn’t work as I predicted. But, as I have often noted on the air, pre-emergent herbicides are just one tool to use in keeping weeds at bay, and they are never 100% effective in blocking weed seeds from germinating.
They’re just part of the plan, along with following my lawn care schedule Randy’s Lawn Care Schedule and mowing correctly (tall for St. Augustine, reel mowers for Bermuda). Plus, Mother Nature has to cooperate – no pre-emergent herbicide will work if a recent application gets washed away with a 2-3 inch rain.
Having a thick, healthy stand of turf is a natural form of weed prevention. Weeds simply cannot germinate in a St. Augustine lawn that is mowed tall and fertilized appropriately. In my business, Randy Lemmon Consulting, I see it all the time. Lawns covered up in weeds are probably the most poorly cared for. I always see that the St. Augustine is mowed too short, and there’s no organic matter in the soil. And while some may cut their Bermuda lawns with a rotary mower, and claim they follow my schedule, I find they’ve never done a core aeration or a compost top-dressing.
Those are all important procedures to employ if you want a good-looking lawn in the Gulf Coast region. And a single application is never going to keep a yard weed-free. Especially if it’s quickly followed by a major gully washer. Remember pre-emergent herbicides prevent weeds. Post-emergent kill weeds that are already up. This is from one of my recent books, which we call the Top Ten Rules of Herbicides:
GARDENLINE TOP TEN RULES OF HERBICIDES:
- Pre-emergent herbicides block weed seeds from germinating. They will not kill weeds already up. (Use the fertilizer schedule as it will give you a healthier yard — ultimately the best defense against weeds. Period.)
- Once a weed is up, you need a post-emergent herbicide, such as broadleaf weed controls for clover, etc.
- There’s a difference in post-emergent herbicides. Some are “selective,” and some are “non-selective.” Glyphosate herbicides (Roundup, Eraser, and even organic vinegar solutions) are non-selective — they kill every kind of weed or grass. “Selective” herbicides usually target a specific category of weeds – broadleaf, grassy or sedge.
- If you’re late with the application of pre-emergent herbicides, you can still do it. You just may not get total control, as some weeds may have already germinated.
- Know the temperature restrictions on most “selective” herbicides. For example, we now have cool-season herbicides for broadleaf weed control. We didn’t have that 30 years ago. It’s also why we don’t used products like Image when it’s too hot.
- Although it can control a few broadleaf weeds, the powdered organic grassy-weed control known as Garden Weasel AG Crabgrass from Agra Lawn was originally designed for grassy weeds. But I have had personal success with it on Virginia Buttonweed.
- Nutgrass and nutsedge are neither grassy nor broadleaf weeds, which is why I recommend specific sedge controls for those annoying weeds.
- The granular version of Bonide Weed Beater Complete is a real one-of-a-kind product — a pre- and post-emergent herbicide in one bag. The “pre” is essentially Barricade, which blocks broadleaf and grassy weed seed germination. But the “post” only works on broadleaf weeds.
- Surfactants are neither applicable nor necessary for granular pre- or post-emergent herbicides.
- Surfactants should be added to pretty much every liquid herbicide so the treatment actually sticks to the weeds.
My fertilization schedule strongly encourages a pre-emergent herbicide in October. The overall schedule calls for three separate applications over the year, but the October application, in my horticulturally-seasoned opinion, is probably the most important. That’s because the turf will go into dormancy once soil temperatures get below 55 degrees, and that’s when weed seeds become opportunistic. As a result, we can get overrun by clover, chickweed, poa annua and others in December and January.
If you have a thick stand of grass, and all is working well and looking good, you may be able to eliminate the pre-emergent herbicide applications on the schedule. Well cared-for turf that has a deep root system and a dense growing pattern is its own best defense against weed seed germination. But if you’re not among those folks, get as many bags as you need and get busy right now.