To Roundup or Not to Roundup That is the Question

By Whitetail Institute Staff

No doubt about it, the world of food plots has evolved tremendously. Gone are the days of people asking what a food plot is. Also gone is the question of whether food plots are a viable tool in habitat management and improvement. Over the past few years the questions our consultants are asked have shown a trend — today more than ever before, our field testers are asking questions that are much more advanced.
One example of this is the relatively recent increase in the number of questions we receive about the uses of herbicides in the planting and maintenance of food plots. The Whitetail Institute, in keeping with its leadership role in the industry, introduced the first ever line of herbicides designed for food plots. Two years ago, Arrest (grass control) and Slay (broadleaf weed control) burst onto the market with incredible fan-fare. Even with the tremendous success of these two products, there is still little debate about what herbicide the Institute is asked about most of all — Roundup.

Roundup, a Monsanto product, is a broad spectrum herbicide that for years has been well known to farmers, gardeners, homeowners and literally anyone with a green thumb. Roundup can be found at nearly every store that has anything to do with growing plants and is arguably the most widely used herbicide on the market. Roundup is a “non-selective” herbicide, which means that it kills indiscriminately.

The questions our consultants handle have also shown that there is still quite a bit of confusion about Roundup and how it can be effectively and safely used in a food-plot application. In this article we will examine the what, how and when of Roundup usage and hopefully answer some questions you may have. And, as always, feel free to call our in-house consultants if you have additional questions. The call is toll-free, and the number is (800) 688-3030, ext. 2.


The active ingredient found in Roundup is “glyphosate.” Glyphosate kills plants by inhibiting a specific enzyme that is needed by plants for growth. This enzyme is called EPSP synthase, and it is essential in the production of proteins needed for normal plant growth. When this enzyme is inhibited by glyphosate, these growth proteins are not produced, and the plant will begin to yellow and slowly die over a period of days. Glyphosate is effective on nearly all green vegetation as this same enzyme is used by most plants.


Glyphosate is considered a post-emergent herbicide. “Post-emergent” means that it is for use on plants that are “already growing.” But be sure you understand — it means that the plants to be CONTROLLED must already be growing — it does NOT mean that it should be used on FORAGE PLANTS that are already growing. Remember, Roundup controls to varying degrees any growing plant it touches.

One important characteristic to understand about glyphosate is that it does not have a soil residual — once it is taken in by the leaf of a plant, it controls that plant and does not leave a soil residual. That means that it will not prohibit you from planting for more than a matter of days. On the downside, though, it won’t control weeds that grow from seeds after Roundup has been sprayed either. The leaf of a plant is the principle means by which Roundup is absorbed. Therefore, adequate glyphosate-to-leaf contact is important. The efficacy of some glyphosate herbicides may be increased by adding certain adjuvants such as surfactant or crop oil. There are a host of glyphosate herbicides on the market these days, and while some may benefit from the addition of adjuvants, others may not. That question, and any others you may have about the use of a particular herbicide you are thinking of using, may be resolved by reading the herbicide label.

If an adjuvant is called for, two common types are generally referred to as “surfactants” and “crop oils.” A surfactant is a chemical that helps an herbicide spread on the leaf, stick to it or penetrate its cuticle. This is why you may have heard surfactants called “stickers” — they generally help the herbicide stay on the weed’s leaf and get into the plant better. Crop oil (also sometimes called “crop oil concentrate” or “seed oil”) is another kind of adjuvant, and it increases the rate at which an herbicide is absorbed by the weed’s leaf. Crop oil is often used when spraying some selective grass herbicides to control hard-to-kill grasses like fescue or Johnsongrass.


Glyphosate can be a very effective tool when preparing a seedbed for planting, and understanding its characteristics and relating them to the appropriate application will give you better results. The most common use of glyphosate by food plotters is in preparing a seedbed in a fallow field, or when preparing to replant an existing food plot that has been overtaken by weeds. When planting a food plot in an area that has not been planted before, or at least not recently planted, it will more than likely be over-grown with weeds and/or have a heavy sod base. In situations where breaking the ground is appropriate, it can be a beneficial step in creating a good seed bed. Unfortunately, this can be the hardest step for some food plotters to accomplish, especially if they are trying to turn the soil with ATV implements. The root structure of existing vegetation creates a tight, dense layer in the top few inches of soil. If you are using light equipment such as a 4-wheeler implement, the initial breaking of the ground can be an arduous task because these implements usually do not have sufficient weight to efficiently break through the sod base. Breaking heavy sod with light equipment will take some time and will more than likely not kill the entire root structure of the plants. In these cases, spraying Roundup before you try to break the ground can make your lighter tillage equipment much more effective. The reason is that glyphosate kills the entire plant, including its roots, and when the roots die they release their grip on the soil, allowing you to disk it much more effectively with light equipment.

If you find yourself faced with this scenario, first examine the existing vegetation. Are the existing weeds tall or mature? If so, you may want to mow the area first. This will help you in two ways. First it helps to break down the heavy ground cover, allowing your equipment to operate more efficiently. Second, it can help the weeds take in the herbicide better. When a plant is mowed, it goes into shock for a week or so. Once it recovers from the shock of mowing, it will start growing vigorously to try to replace the foliage it lost when it was mowed. Spraying after this re-growth starts can help make the herbicide application even more effective. So, if you do mow, wait until you see new growth appearing again (usually a week or two after mowing) before spraying.

Most glyphosate herbicides take 10 to 14 days to completely kill the plants, so you will need to allow about two weeks between spraying and breaking the ground. If you have heavy equipment such as turning plow or PTO driven tiller, you will likely not need to use Roundup before you break the ground since the equipment you are using will cut through the roots, killing the vegetation.

However, repeated or deep tilling may not be as effective at killing some grasses, which grow from their root systems, as they can be in controlling weeds that rely on reseeding. Also, as we mentioned earlier, glyphosate will not kill the seeds in the soil. The Institute has fielded many field-tester questions asking why grass and weeds reappeared even after they had sprayed Roundup and tilled the plot. The answer is that there can be literally millions of plant seeds in the ground, and some can survive for decades in dormancy just waiting for the right conditions for germination. Spraying kills the weeds on the surface, but if you till the ground again after spraying Roundup you will likely bring dormant seeds to the surface and reinfest the plot To try and help with this predicament, here is a method that may be the best way to get as close to a weed-free seed bed as possible. The key is to not turn the soil again after the second RoundUp application so that you don’t bring up more dormant weed seeds.

1. If needed (existing thick, tall and mature vegetation), mow weeds to a height of about 6 inches,

2. Wait until you see grass and weeds starting to put on new growth (usually after a week or so),

3. Spray Roundup or another glyphosate herbicide as recommended on the herbicide label,

4. Wait approximately 10-14 days for a complete kill on existing vegetation.

5. Till the soil (adding any lime needed to raise soil pH before you till), and smooth the plot with a drag or cultipacker (roller).

a. Example: Planting Imperial Whitetail Clover
i. Disk the ground several times.
ii. Run a drag over the ground to level the seed bed.
iii. Go over the seed bed with a cultipacker to further level and firm the seed bed.

6. Wait approximately 2 weeks for new weed seed to begin growing.

7. Apply Roundup or other glyphosate herbicide again.

8. Wait 5-10 days for new weeds to begin dying.

9. Without doing any further tilling, seed the food plot and go over it with the cultipacker for good seed-to-soil contact. (But, do NOT drag over Imperial perennial seeds or otherwise cover them.)

Without question this method requires planning and time. The process can take up to four to six weeks to complete. But with a little patience and planning, you can produce as close to a weed-free seedbed as you can get. This method is especially effective on fields that have a history of being very weedy.


In the past couple of years, there has been much talk about using a very low-concentration, or “watered-down”, Roundup application on perennials such as Imperial Whitetail Clover to kill the weeds but not kill the clover. There are several reasons why the Institute does not recommend this practice. First and foremost, this practice is contrary to the instructions on the Roundup label. You should always read, understand and follow all herbicide label directions — on Roundup or any herbicide. Failing to follow an herbicide’s label instructions can reduce the efficacy of the herbicide, kill your plot, harm the environment or have other negative consequences. The label instructions are there for a reason, and in the case of Imperial Whitetail Clover and any other plant you want to save, one reason is this: Glyphosate herbicides can damage or kill any plant they touch. There is no standardized science to using watered-down glyphosate for applications not specifically listed on the herbicide label, and there are quite a few variables that will affect it. Some of these variables include sprayer calibration, ground speed, wind, rainfall, plant maturity, improper mixing and host of others. A problem with any one of these variables can cause your beautifully green Imperial Clover field to turn brown and die. With that being the case, and with selective herbicides available that ARE appropriate for controlling grass and broadleaf weeds in Imperial Whitetail Clover, there seems to be little reason to run the risks associated with using glyphosate off-label. A far better approach is to use herbicides for their designed purposes, and there are selective herbicides available, such as the Institute’s Arrest and Slay herbicides, that are designed to control grass and broadleaf weeds in Imperial Whitetail Clover.

Without question, Roundup can be an extremely effective tool in preparing seedbeds for planting food plots. Realizing how it works, when to use it and how to use it will help you maximize your efforts.