You Only Need Four Post-Emergent Herbicides

by | May 12, 2022 | herbicides, Weeds

It’s the most asked question of Extension agents everywhere.  “What is this weed and what herbicide should I buy to kill it?”  The first part of that question is straightforward.  Between personal field experience, formal plant identification training, and a team of weed science specialists to call on, Florida Extension Agents can get your weed accurately identified.  The second part of the question is slightly more nuanced.  Many weed problems can be avoided by following lawn and landscape Integrated Pest Management (IPM) practices, like not overwatering, mowing at the correct height, using mulch where you can, etc., but sometimes herbicides are required.  For these situations, if you follow the “homeowners only need four post-emergent herbicides rule”, you’ll be ready for any weed challenge you face!*

Doveweed seedlings just emerged on July 9, 2021. Photo courtesy of Daniel Leonard.

The first weed scenario you should be prepared for is spot spraying weeds in landscape beds and around hardscapes like concrete pads, sidewalks, pools, driveways, etc.  For this situation, you’ll turn to the backbone of the four herbicides rule and a staple in any weed management program, glyphosate.  Glyphosate is the active ingredient (AI) in many non-selective products ranging from the infamous Roundup brand to cheaper generics like Killzall and Cornerstone.  Glyphostate is extremely cost-efficient and very effective on a huge range of emerged weeds including grassy weeds, broadleaf weeds, and even sedges (also called nutsedge or “nutgrass”).  Just be sure not to get any overspray on desirable plants or they’ll be seriously damaged!

The second situation we face occurs when “bad” grassy weeds invade landscape beds, shrubs, and vegetable gardens.  These cases call for a grass-selective herbicide that you can spray right over the top of your broadleaf annuals, perennials, and shrubs to take out the unwanted grasses.  In this case, there are two options at your disposal:  sethoxydim (AI in many products like Fertilome Over the Top, Hi-Yield Grass Killer, Poast, etc.) and fluazifop (AI in the product Fusilade).  Both products work well in removing weeds like crabgrass, bermudagrass, goosegrass, and others and can be safely applied over the top of many ornamentals.

Seeds from annuals like Chamberbitter easily get into mulch and turfgrass from surrounding areas. Photo by Beth Bolles, UF Extension Escambia County

From time to time, we need to treat a broadleaf weed like dollarweed, doveweed, chamberbitter, or any number of others, that have invaded our lawn grass.  Some of these weeds are tougher than others, but almost all of them can be managed with the proper rates of 2,4-D, Dicamba, other similar products, or a combination of several of them.  These active ingredients have been on the market for decades so there are many generic options at your disposal.  However, if you have a truly tough broadleaf weed problem, the newer product Celsius WG from Bayer (a combo of Dicamba and two newer AIs), while a little pricey and only available online or at specialty chemical dealers, is well worth the expense and knocks out the most gnarly of lawn weeds.

Finally, there is a category of weeds that aren’t broadleaves and aren’t quite grasses either.  These are the sedges.  Commonly known around the Panhandle as “nutgrass”, sedges are a serious pest of lawns, particularly those that stay a little on the damp side, and vegetable gardens.  Sedges, with their glossy leaves and distinctive flowers, stand out in lawns and gardens, are very unsightly in an otherwise well-maintained area, and can outcompete the desirable plants they invade.  Fortunately, there are several AIs that work very well on sedges and are safe to use around turfgrass and many other plants.  The most effective sedge herbicide AI for homeowners is halosulfuron-methyl (AI in Sedgehammer in lawns and Sandea and Profine in vegetables).  Sedgehammer works very slowly (results can take up to a month) but is very safe in turfgrass and ornamentals and highly effective!  If Sedgehammer and other halosulfuron products are difficult to obtain, Imazaquin is a slightly less effective but more common substitute.  This AI can be found in the product Image Kills Nutsedge and is safe for use in turfgrass and most ornamental plantings.

The challenge of controlling the many types of weeds in your lawn, landscape, and vegetable garden seems daunting, but having just four basic classes of herbicides on hand can greatly simplify things!  Whether you need to control a broadleaf, grass, or sedge weed problem, putting together a weed control toolbox containing a non-selective herbicide like glyphosate, a broadleaf selective like 2-4,D, a grass selective like sethoxydim, and a sedge selective like halosulfuron-methyl can allow you to handle most any weed you come across at home.  For more information on controlling weeds in home landscapes and gardens or any other horticultural topic, contact your local UF/IFAS Extension office.  Happy gardening!

*Most homeowners discover weed problems after the weeds are already up and growing, making post-emergent products necessary.  Pre-emergent products have a place in weed management programs but are not the focus of this article.

Daniel J. Leonard
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