There is not a week that goes by that we don’t hear of a weed problem that can’t be solved by using “Roundup.”
I have said Roundup for years, but what we really mean when recommending a non-selective herbicide is glyphosate. Roundup is actually the registered brand name from Monsanto that contains the active ingredient called glyphosate.
In the early 1970s, two chemists working for Monsanto took a compound that was being studied for a water softener and saw the potential for an herbicide.
On their third try, a compound they synthesized would forever change the face of farming. This molecule was named glyphosate. It is a non-selective herbicide, meaning it kills virtually all plants with which it comes in contact.
The good news was that glyphosate was found to decompose rapidly into the natural products carbon dioxide, phosphoric acid and ammonia, so it is considered to have little effect on the environment. It also doesn’t last in the soil, so it is considered safe for humans and wildlife.
With this new herbicide available, Monsanto made huge investments into the development of genetically modified seed that would be resistant to glyphosate.
They developed crops like canola, soybeans, corn and cotton that you could spray glyphosate directly over the top of for weed control without harming the crop itself. They labeled the crops as Roundup Ready and, for farmers, it was a game changer.
From an agriculture standpoint, the good has far outweighed the bad, but there have been some drawbacks to this method of farming.
Some weeds have become resistant to glyphosate, such as the dreaded Palmer pigweed that has invaded cropland. Methods to combat these issues can cause some major headaches.
Since its patent expiration in 2000, glyphosate has been marketed by many companies. For most of my readers, homeowner uses for glyphosate are mostly what I recommend.
The best way to use glyphosate is, of course, to follow the label attached to the container, but my highlights include a few best methods:
Weeds need to be actively growing to be affected by glyphosate. The pores on the weed leaves will need to be open to absorb the chemical to kill them. Make sure the weeds to be sprayed are hydrated. If it rains a day or two before, and the plant is perked up and growing, this will assure proper intake of the chemical.
Additives to your mixture can help in various ways. For waxy-leaved plants like English ivy, add in a surfactant that helps the mixture “stick” to the leaves to insure absorption. When spraying large areas, try using a marking ink. The blue ink will let you know where you sprayed and didn’t spray by adding a tint of color. The ink washes off or fades in a couple of days.
Glyphosate needs to be sprayed on the foliage to kill the plant. Spraying the chemical on the ground or the bark of a tree will have no effect. The caveat to that is that at a full concentrate, glyphosate will kill a plant from the bark if it penetrates a fresh wound.
Mix the chemical with water and use the entire spray bottle in a timely manner. When glyphosate is diluted with water, it needs a compatible pH usually not found in our city water supply to remain in its most effective state. Therefore, the shelf life is only a couple of days before it breaks down to a level that is ineffective.
Be careful what you spray. I have heard a lot of stories of people killing things like Gerber daisies and astilbe before they matured because they look like some weeds. Others spray pine straw beds, walk back through the chemical on the ground and cross the lawn. This makes for some nice brown footprints across the green grass for the rest of the growing season.
Glyphosate doesn’t kill all plants. At annual weed control concentration levels (i.e. 3 ounces per gallon of water), larger trees and shrubs may get a slight burn, but probably won’t get killed. Some plants have to be at a certain stage of growth for the glyphosate to be effective. For instance, poison ivy can be controlled when sprayed during the flower or fruit stage. Earlier applications are not as effective.
If you have a large plant or vine that isn’t reacting to foliar spray, drill a hole in the woody part of the plant and immediately add a straight glyphosate concentrate. A ¾- to 1-inch hole is ideal. Other areas where the vine isn’t large enough to drill, cut the plant and immediately paint concentrated glyphosate on the wound. That is a good method to get greenbriers that have infested your shrub beds.
Reach Campbell Vaughn, the UGA Agriculture and Natural Resource agent for Richmond County, by e-mailing firstname.lastname@example.org.