Roundup is Roundup…Right?

Tony Koski, Extension Turf Specialist

Which one do I use? They both say  Roundup!

If you are reading this in hopes that the turf specialist has seen the light and jumped on the Occupy Monsanto bandwagon, well…you can stop reading now. Glyphosate/Roundup is still, in my opinion, one of the most effective, inexpensive, easy-to-use and safest herbicides available to the home gardener – and to professional weed managers as well. But a stroll through the pesticide aisle of any hardware store or big box garden center can present to even the sharpest of gardeners a somewhat bewildering selection of Roundup products from which to choose…Roundup Concentrate…Roundup Concentrate Plus…Roundup Extended Control. The various Roundups entice you with promises like “Results in 12 hours” (faster is always better…right?) or “Controls weeds for up to 4 months” (longer is always better…right?). And then there is yet another glyphosate-containing product, ominously named GroundClear, which provides one year or more of weed control (REALLY longer is BEST…right?). It’s easy to understand the confusion when asking oneself “Which one do I buy?”. And I suppose it’s somewhat easy to understand when consumers (professional applicators don’t get a break here) misuse these products in the landscape – although a thorough reading of the label would, in most cases, prevent some damn dumb mistakes. (What? Read a label? Ain’t nobody got time for that!). Sooo….how different are these Roundup products? Can they be used interchangeably? Is one better than the others? Are all of them “safe” for home landscapes?

First, the traditional verbiage – to protect my you know what – whenever we Extension types write about pesticides: READ THE LABEL before purchasing, much less using, any of these products! A reading of the ingredients section of the various Roundup products demonstrates that they aren’t the same. And while the "where to use/not to use" instructions aren’t always the most clearly written, a close reading (ok, maybe 2 or 3 times…) of the label will help prevent misuse of these products. 

Roundup Super Concentrate (white bottle…purple cap) is your good ol’ pure and simple glyphosate.  Use it wherever (wherever the label allows, that is…yes, READ THE LABEL!) you need non-selective control of weeds in your landscape. It is taken up only by leaves and other above-ground green plant tissue. No soil residual. No root uptake. No extended control.  This Roundup can be safely used: on your driveway or sidewalk or patio…on mulch circles around trees (but don’t spray the trunk, or surface roots, or suckers)…to renovate your lawn…or to kill a section of your lawn and replace it with a flowerbed or veggie garden. This is the slowest acting Roundup product, taking anywhere from 5-10 days before you begin seeing symptoms that the weeds are dying. But because we are so impatient (we “need” FASTER internet… FAST food…RAPID transit…INSTANT mashed potatoes), a couple of other Roundup products were developed to satisfy consumer demand for more rapid weed kill. Enter Roundup Plus…

Faster Roundup is better....isn't it?

Roundup Concentrate Plus (white bottle…red cap) contains glyphosate and another herbicide called diquat dibromide. The diquat is added to give a more rapid burndown of weeds that have been sprayed. Other than providing the more rapid (within about 12 hours during hot weather) visual symptoms that the weeds have been sprayed, this Roundup product works the same way as the basic concentrate. All foliar absorption, no root uptake or soil residual. No extended control. 

Roundup Ready-to-Use Plus (blue and white bottle) contains glyphosate and pelargonic acid. The pelargonic acid makes this Roundup product work even more quickly than the Roundup Concentrate Plus – you may see wilting within 3 hours on a hot, sunny day. So, for the VERY impatient, this Roundup product works even more quickly than the Concentrate Plus product – but is otherwise the same: all foliar uptake, no root uptake, no soil residual, no extended control. Use it the same way you would the above two Roundup products.

Roundup Extended Control (gray bottle) contains pelargonic acid (for rapid burn down) and a herbicide called imazapic. Imazapic is added to provide the “extended control”. It works as a preemergence herbicide to provide 3-4 months of weed control by killing germinating seeds/seedling weeds. However, imazapic also is somewhat root active and can provide postemergence control of some weeds as well. This is where things get tricky. Imazapic is fairly water soluble, so it can move in soil. This means it can move to parts of the landscape where you haven’t sprayed it (down slopes, for example…or when sprayed on gravel-covered plastic). And because of the long soil residual, don’t use this product where you may want to plant something in the near future (so this one is a no-no for lawn renovation, nor should it be used where you plan to plant a veggie or flower garden in the future…or trees or shrubs).  The label does allow use over the root zone of trees and shrubs (established ones…not newly planted), including on mulch circles around trees. However, imazapic has been shown to cause injury to a

few tree species which are sensitive to it: lindens, green ash, and cherry trees. Soooo….while it is generally safe to use in those parts of the landscape where you need control of existing weeds AND desire some long term weed control/prevention, you have to recognize the potential for this stuff to “move” in the landscape. Use the same precautions that you would with any Roundup product…and maybe consider if you REALLY need to use this over the root zone of your trees? 

And then there is GroundClear….While it doesn’t have Roundup prominently displayed on the label, this is another Roundup product. It is aggressively marketed on the radio and in the aisles of big box stores. Who wouldn’t want weed control for a year - or longer? This is the one where the “Keep out of reach of children” line on the label maybe should read “Keep out of reach of adults who don’t read a label”. This Roundup product contains imazapyr (a close relative of imazapic…see above), which is a VERY long-lasting, soil/root-active herbicide. Imazapyr can last a year or longer in soil, depending on soil type and how much moisture the soil receives. It is non-selective, can move with water in soil, and is easily taken up by roots of trees (yours or your neighbor’s), shrubs, vines, flowers, veggie plants, turf….you get the idea. As the name would imply, this product really does “clear the ground” on which it is applied. In my opinion, there are few places in a home landscape where this product could be safely used. I doubt that there is a driveway, patio, or fence line in any urban landscape that doesn’t have a tree or shrub root growing under it. Unfortunately, the promise of long-term weed control is so irresistible, it is bought and used in places where there is significant potential for damage to trees and other desirable landscape plants. This is one that you want to avoid using in your landscape, unless you REALLY, REALLY know what you are doing – and even then I would be hesitant to use it.  I have visited landscapes where professional applicators (who should know better…and who violated the label by using it where they shouldn’t have) have killed or injured dozens of trees using this and similar products for mulch circle weed control.

Trees killed by improper use of herbicide
containing imazapyr.

Like most things in life - when preventible, bad things happen - you can only blame yourself for not reading (or following) instructions and heeding warnings.  When you purchase any pesticide, you enter into a legal agreement that you will use it as the label instructs. Your trees and turf can’t read the label…they trust that you will.