Roundup for Lawns? Will It Kill My Lawn?

By Gil Medeiros
There is a new product for 2017 called Roundup for Lawns. No, it will not kill your lawn unless you use it improperly. But if you are a little confused about the product name, it shows you have been paying attention!

Before this year every Roundup product since its introduction in the 1970s has been a broad spectrum, post-emergent herbicide. Roundup has always killed weeds AND the grass around the weeds — essentially every green vascular plant. The active ingredient has always been glyphosate. (For some products, Monsanto has added other compounds to increase the range of plants that the product killed.)

Roundup, the trade name, and glyphosate, the active ingredient, became synonymous.

This year Monsanto — with its marketing partner Scotts — has entered the market to kill broadleaf weeds in turf. The market is already served by familiar products such as Weed B Gon made by Ortho, (which is a subsidiary of Scotts), Trimec and Speedzone, both sold by HBI Gordon. The marketing wizards at Monsanto-Scotts chose to call the new product Roundup for Lawns and not Four-Way Lawn Weedkiller from the makers of Roundup.

One thing is clear: Roundup for Lawns does not — repeat not — contain glyphosate.

It DOES contain the same old stuff as most of the existing selective herbicide products for lawns, which begs the question: Why go to the expense of introducing a new product? Did the world really need another selective weed killer that differs from the field in brand name only? I guess the market will provide the answers.

Let’s review briefly the chemical make-up of some popular, post-emergent, selective herbicide products. The main way to kill broadleaf weeds in lawns is to apply chemicals called synthetic auxins, which mimic natural plant growth regulators (auxins). Synthetic auxins cause broadleaf plants, but not grasses, to lose control of cell growth and eventually die. The first of these synthetic auxins, 2, 4-D, was introduced in the 1940s and is still commonly used. Many variants have been synthesized over the years, but MCPA, MCPP, and Dicamba are often used with 2, 4-D to extend the effectiveness of selective, broadleaf weed control products. You should not be surprised, then, that the new Roundup product is based on the same basic set of active ingredients as Weed B Gon, Trimec, Speedzone and many other products. The percent compositions may differ a little, but the ingredient lists are about the same.

Some, but not all, formulations of Roundup for Lawns are labeled for control of crabgrass. These contain Quinclorac, another synthetic auxin, for that purpose. Also, I list the ingredients for basic Weed B Gon. However, there is a family of Weed B Gon products. One of them controls crabgrass along with broadleaf weeds and contains Quinclorac. There is one that controls oxalis, chickweed and clover. It contains only Triclopyr, a synthetic auxin that is chemically different from the others.

PBI Gordon, which is perhaps better known for its professional products but has a significant following among homeowners in Fairfax County, has an extensive line of products as well. Some contain Quinclorac for crabgrass; others contain Glyphosate to control weeds and grasses.

Roundup for Lawns is very similar chemically to the others, except that it contains Sulfentrazone. Speedzone differs from the norm in that it contains Carfentrazone. These ingredients are similar chemically but have different functions. Sulfentrazone is the main ingredient in products sold by several companies to control sedges in lawns. Therefore, its presence in the formulation adds sedges to the list of controlled weeds for Roundup for Lawns. This poses a small problem, however. Yellow nut sedge, the most common sedge in Fairfax lawns, comes up in the hot weather of mid-summer. Just about all phenoxy (e.g., 2, 4-D, MCPA, MCPP) synthetic auxin-based herbicides have upper temperature limits for their use. They volatilize in the heat and can harm other nearby plants. In my opinion, it is safer for your landscape to use a product that contains only Sulfentrazone to control sedges in the heat of summer, rather than a mix such as Roundup for Lawns.

Carfentrazone in Speedzone acts on broadleaf weeds, not sedges, and has an almost immediate effect. This ingredient accounts for the speed in the name Speedzone and much of the loyalty that users have for this product.

So we will watch for online reviews later in the season to see what users think about Roundup for Lawns. I predict the reviews will look very similar to those for Weed B Gon since the products are very similar. Can Roundup for Lawns find a niche in the selective herbicide market? If Coke and Pepsi can coexist, I suppose Roundup for Lawns and Weed B Gon can, too.

References
Weed Control, (Ortho),
It’s a Good Day to Be a Lawn, (Roundup for Lawns)
Lawn and Garden (PBI Gordon)