Pre-Emergent Herbicides - The Complete 2020 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, two of the most readily available.

Some say they have more weeds than ever and are bummed because the products didn’t work as I predicted. But, as I’ve noted before, pre-emergent herbicides are just one tool for keeping weeds at bay, and they are never 100% effective in blocking weed seeds from germinating.

Pre-emergents are just part of the total plan that includes 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 Randy Lemmon Consulting business, 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 follow for a good-looking lawn in the Gulf Coast region. And a single pre-emergent application is never going to keep a yard weed-free. Especially if it’s quickly followed by a gully washer.

GARDENLINE TOP 10 RULES OF HERBICIDES:

  1. Pre-emergent herbicides block weed seeds from germinating. They will not kill weeds already up. Use the fertilizer schedule to have a healthier yard, ultimately the best defense against weeds. Period.
  2. Once a weed is up, you need a post-emergent herbicide. For example, a broadleaf weed control for clover.
  3. There are different forms of post-emergent herbicides. Some are "selective," and some are "non-selective." Glyphosate herbicides (Roundup, Eraser and 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.
  4. 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.
  5. Observe any temperature restrictions of selective herbicides. For example, we now have cool-season herbicides for broadleaf weed control. We didn't have that 30 years ago. And we don't used products like Image when it's too hot.
  6. The powdered organic Garden Weasel AG Crabgrass product from Agra Lawn was originally designed for grassy weeds, although it can control a few broadleaf weeds. I have had personal success with it on Virginia buttonweed.
  7. Nutgrass and nutsedge are neither grassy nor broadleaf weeds. I recommend sedge controls for those.
  8. 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.
  9. Surfactants are neither applicable nor necessary for granular pre- or post-emergent herbicides.
  10. 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, and today is Oct. 1. Overall, the schedule calls for three applications during the year, but the October application, in my opinion, is probably the most important. 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 actually be able to eliminate the pre-emergent herbicide applications on the schedule. Well cared-for turf with 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.

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