We’ve all been there: you spray weeds hoping your application takes care of the problem, only to realize a few days later that your hard work has gone without reward and the weeds remain. This can be especially frustrating when you are treating a large area of weeds that are threatening other plants. The longer they remain, the more destructive they can be. It seems that the only solution is to simply reapply more herbicide, but an easier, safer, cheaper fix is available: adding a surfactant to the mix.
Weeds are always tough to eliminate but there is a bit of science involved to weed killing. For maximum effectiveness, a post-emergent herbicide has to come in contact with plant leaves and remain on leaves long enough to be absorbed into the plant and reach the parts of the plant that will damage or disrupt a vital process in the plant. The waxy outer layer and cuticle of leaves are barriers to these chemicals.
The waxy layer and cuticle are very strong barriers to water and most herbicides are carried in water. Water, while an excellent solvent also has a very high surface tension. This means it will bead up on waxy surfaces and the water can easily bounce or roll off. Just like when you apply wax to your car to keep water from drying on your car and roll off, this same action applies to leaves of plants.
This bouncing and rolling will affect you in multiple ways: your weeds will not die, some of your desired plants or grasses might die instead and you will spend more money on herbicides than you had intended. All three outcomes could be very frustrating. When treating weeds without a surfactant added, you not only run the risk of letting your weeds remain, but also using double or even triple the amount of chemicals you initially planned, which can cost you more money and add an overdose of chemicals to the environment.
Adding just a dash of surfactant can increase the effectiveness of all your herbicide applications. A surfactant, a combination of the words “surface active agent,” is an organic compound that is soluble in chemical solutions or water and allows mixtures to blend, adhere and work better. They help to break the barrier between unlike chemicals or surfaces, like the waxy surface of a leaf.
Surfactants work because they’re able to break the surface tension of the herbicide and leaf surface. This allows the spray to evenly coat leaf surfaces in an even sheen with no beading up or rolling off. The herbicide will then be allowed to sit on the leaf surface long enough for the herbicide to be absorbed, and the reduced surface tension aids in absorption. This will dramatically increase the weed-killing power of your herbicide and reduce the risk of drift and runoff to desirable plants.
Some herbicides actually need surfactants in order to work, but other products might already have surfactants added in. Make sure you read all labels thoroughly before adding anything to your herbicide. When looking for a surfactant to purchase to use with an herbicide, always look for a nonionic surfactant. The label of your herbicide should suggest the proper type of surfactant.
There are a handful of different types of surfactants, but nonionic are the most universal and work best with herbicides. Some people choose to add dish soap to their herbicides, because dish soaps do have surfactants added and they are very inexpensive. While it may work, if it isn’t nonionic, it could interfere with the chemical processes and prevent the herbicide from doing its job.
Most surfactants are fairly inexpensive and widely available. Surfactants improve spreading, sticking and pesticide uptake. They are sometimes called “wetting agents” or “wetter spreaders,” and while they do help completely wet leaves with herbicide, they are not always the same thing as wetting agents, wetter spreaders and sticker spreaders. These all fall into a category of adjuvants, which are additives that can affect how the herbicide or other chemical functions. So, all surfactants are adjuvants, but not all adjuvants are surfactants, so pay attention to what you are adding for your desired results.
Adding a surfactant to your herbicide regimen is nearly risk-free. It will help boost the effectiveness of your herbicides to ensure the product kills your weeds quickly and completely. Surfactants are safe when used as directed and have a low toxicity to other plants and animals.
If you do choose to use add a surfactant to your weed control regimen, it will be for post emergent control, for weeds that have already emerged out of the soil. Since herbicides work to interrupt photosynthesis, protein synthesis and root growth, among other life processes and it can be really tricky to get all the factors right for application.
Remember to keep these things in mind: Remember to spray herbicide directly onto the foliage of individual plants on all sides and make sure to contact the growing tips and bud terminals. Try to make sure all leaves are completely covered in your product. Timing is a huge part of weed control and applying when plants are actively growing is very important for quick control. Applying in spring, when plants just emerge and in fall when plants are storing up nutrients in their roots, can speed up the killing process. Warm, calm, sunny days are best days for application.
Don’t apply herbicides in drought or in conditions that might prevent plant growth. Windy days can be dangerous for application, as the chemicals can drift to desirable plants and in living areas where pets and children might be. Keep kids and pets away from treated areas for a few days to ensure safety.
When you are applying herbicides, always wear proper safety equipment including eye protection, proper attire to protect skin and in some cases, masks for respiratory protection. Always read the labels in any product you use in your garden or lawn. Not only do these labels help keep you safe, their instructions are the law.
Jenny Gagas is a research specialist for Do My Own Pest Control.