Garden Tips: A Roundup on how to fight weeds

Most gardeners know about an herbicide called Roundup. The first products on the market called Roundup contained glyphosate. Glyphosate was discovered in 1950 by a Swiss chemist working for a pharmaceutical company.

However, its perennial weed-killing activity was only uncovered in the early 1970s by a Monsanto Company chemist looking for compounds that could serve as water softening agents. This led to his development of the powerful herbicide glyphosate that Monsanto patented and marketed under the trade name of Roundup.

In 1974, Monsanto released its first Roundup products in the U.S. After Monsanto’s glyphosate patent expired in 2000, a number of other companies have been marketing herbicide products containing glyphosate under various product names, such as Knockout, Prosecutor, Eraser, Groundclear and more.

On a recent trip to the hardware store, I discovered that Monsanto has continued to add to their home and garden Roundup line, but not all of them contain glyphosate. Here is what I found:

Roundup for Lawns 2: This is a selective herbicide that is intended to be applied to an entire lawn for control of weeds. While it has the “Roundup” name, it does not contain glyphosate. It contains MCPA, quinclorac, dicamba, and sulfentrazone. The MCPA and dicamba kill broadleaf weeds selectively. The other two ingredients are selective herbicides that kill broadleaf weeds and some grassy weeds like crabgrass, foxtail and yellow nutsedge.

Roundup Extended Control: This product is for use on gravel areas, driveways, sidewalk cracks, mulched landscape beds, along fence lines, and other places you do not want weeds to grow. It kills existing weeds and suppresses weed growth for about four months. This product contains glyphosate and two other herbicides, pelargonic acid and imazapic.

Pelargonic acid quickly kills or burns down green tissues to which it is applied, but it is not systemic and does travel through the plant and kill roots. Imazapic is a non-selective herbicide that is absorbed by both plant leaves and roots. Unlike glyphosate that has no residual activity, imazapic stays active in the soil for about four months. Extended Control is a weed killer intended to “knock-them-down and keep-them-down” for a while.

Extended Control is labeled for use “around the base or in mulched beds of well-established (at least 6 months old) plants, trees, and shrubs,” but use it with caution. Do not apply it where there are exposed sprouts at the base of trees or where you intend to plant anything within the next four months.

Roundup Max Control 356: Use this product very carefully. It is intended to kill weeds and prevent their growth for an entire year. It is only for use on driveways, patios, gravel areas, and along fence lines. However, it should never be used in the root zone of desirable trees or shrubs, or in areas that you intend to plant within the next 12 months. It is especially important to note that the roots of trees can reach out as far as the tree is tall and even further. Keep this in mind if you use this product. It is also not for use in lawn renovation or the preparation of vegetable and flower beds.

“Max Control” contains glyphosate, imazapic, and diquat. Diquat is a non-selective herbicide and acts as a burn-down chemical by killing within a few days the green tissues to which it is applied. It does have some systemic activity, but it does not effectively move to the roots and kill them. This product suppresses weeds three time longer than the previous material because the concentration of the imazapic is almost five time greater.

Remember to read the complete label before using these or any other pesticides.

This story was originally published May 26, 2018 at 6:59 AM with the headline "Garden Tips: A Roundup on how to fight weeds."