Pre-emergent herbicides: The whole story

I’ve been peppered recently with emails and Facebook posts 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 noted on the air last weekend, 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 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 protocols 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. Check my Herbicide 101 tip sheet for more about the differences.

I’m emphasizing pre-emergents today because October is when my schedule strongly encourages their use. The plan calls for three separate applications over the year, but the October application 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.