Your Guide to Herbicides
By Tom Peplinksi
I spend a lot of time and money getting things to grow on my farm. Between food plots, apple trees, evergreens, and timber regrowth I’m always trying to get the varieties of plants I want…in the right places, and growing without competition from other plants. When growing food plots I’m targeting weed elimination. When planting evergreens I’m looking to control grasses and other woody species. When trying to improve my timber, cutting out and killing unwanted species like box elder is the goal. The most effective way I’ve found to help me do this is through the careful use of herbicides. Herbicides are plant killers. Each one is engineered and developed to target specific plants at specific times and in different ways. I don’t know how many are out there…maybe hundreds or thousands? I know a lot of hunters who get tripped up and confused when dealing with herbicides. What to use? How to apply it? What rates? When to use them? I won’t make any claims on being an expert or knowing all there is to know about herbicides, but I can help you sort through the questions and break down what I think are the important things to know.
Know the BIG 5
If your goal is to become familiar with hundreds of herbicides and each specialty use…good luck with that. Seriously; there are so many that it’s not practical. However, if you get to know just 5 fairly well, you will have all your bases covered when it comes to weed and plant control.
Glyphosate or as more commonly called Roundup (trade name) is a non-selective post emergent herbicide. Non-selective meaning it kills everything (almost everything). Post emergent meaning it works through contact with the vegetation. The plant must be up out of the ground and growing for the herbicide to work, allowing for a bare minimum of one hour on the plants before it rains. Glyphosate also does not have any residual effects…meaning it kills what it touches but doesn’t affect future weeds. Glyphosate is the all-around versatile herbicide. It is cheap, easy to find, and effective at killing grasses, broadleafs, and woody plants. It will kill all plants that are not genetically altered to resist it. Glyphosate can be purchased under many names like Roundup, Gly Star, Farm Works, and others. I’ve purchased glyphosate in 2.5 gallon jugs with concentrations ranging from 41% to 44% and prices around $50/2.5 gallons. The most common application rate for me is 1 quart/acre which means it costs about $6/acre.
Pursuit herbicide is a grass and broadleaf herbicide suited for weed control in soybeans, alfalfa, and clover. I keep Pursuit as part of my arsenal because of its ability to control both grass and broadleaf weeds in my alfalfa and clover plots. Pursuit works through root or foliage uptake so it can be applied post emergent yet still offers residual control of future weeds. This herbicide has been around a long time and works pretty good. The one down side of Pursuit is its initial cost of about $475/gallon. Application rates are as low as 3oz./acre making the cost per acre about $11. This is one I try to split with other hunters to lower my initial costs. Note: Because Pursuit is a residual, be careful in using on food plots that you intend to over-seed or add to later in the year. The residual effects can and will hamper new growth of varieties like turnips, rape, or rye.
Fusilade is a herbicide that only kills grasses. I like it because if I have a grass problem in a broadleaf food plot like clover or alfalfa, I can target only the grasses. It seems to work better on just grasses than the more all-purpose Pursuit. I also keep it around because you can spray Fusilade directly over evergreens without harming them. Fusilade is a post emergent contact only herbicide that works best on young growing grasses. It costs about $150/gallon and that will cover about 10 acres.
Dichlorophenoxyacetic acid (commonly called 2,4D)
2,4-D is a broadleaf killer. I’ve seen this herbicide under many names. It is a very aggressive and potent killer for all broadleafs including clover, alfalfa, soybeans, pigweed, thistle, burdock, lambsquarter, waterhemp, etc. I have not seen a broadleaf that can survive a spraying of 2, 4-D. I use it in my CRP grass, to kill off troublesome broadleafs in corn, or to kill brushy woody plants. It is the most effective broadleaf killer I know of but won’t harm grasses including corn (corn is in the grass family). The cost is about $30/gallon or $4/acre.
Tordon RTU (Ready To Use) is a liquid I use to treat stumps of unwanted tree species I cut down. Many tree species like box elder are prolific stump growers. If I want to kill the stump after cutting down the tree, treating the cambium layer next to the bark will do the trick.
For all five of these herbicides, I’ve given the basic background on what they do and why I keep them around in case I need them. In each case, reading the label instructions will help you determine rates of application as well as application methods and cautions for use. By far, the most versatile of them all is glyphosate; but glyphosate kills everything right? Well, not genetically altered plants that are called roundup ready (RR).
Imagine using an effective non-selective herbicide that with rare exception kills everything in its path accept the plants in your food plot. In the 1970’s, Monsanto brought glyphosate to market under the trade name of Roundup. In the mid 1990’s Monsanto introduced the first genetically modified plant, a soybean, which would resist glyphosate. Today, the vast majority of corn and soybean crops and a growing number of others are planted in RR varieties. There’s a reason! RR varieties are not affected by glyphosate. And, because glyphosate is a very capable non-selective herbicide, weed control has arguably never been better. When you plant soybeans, corn, canola, alfalfa, and other crops with this trait, weed control is made easy by simply spraying the crop after emergence of the crop and weeds. The glyphosate will kill any weed it contacts but will not affect the modified crop. This is the reason I plant all my soybeans and corn in RR varieties.
The beauty of RR is that you can spray your crops after the weeds are up and growing. Then, as the weeds begin to die off, the preferred crop explodes from the lack of competition and by the time new weeds get a chance to germinate or come up, the desired crop canopies over preventing sunlight from reaching the weeds…smothering them. The key to making this work then is timing. Glyphosate works best on younger weeds, but spraying too early allows new weeds to come in before the crop canopies over. Spray too late and some weeds might get set back but not die. The ideal time is usually between three and five weeks after planting or when the crop and weeds are about 3-6 inches tall.
Application rates for glyphosate don’t need to be complicated. For almost every application, I use 1 quart of chemical per acre. If weeds are really bad, or you experience less than ideal control on tough weeds like thistle or waterhemp for example, increase the rate to 1.5 or 2 quarts per acre. Most of the tougher weeds are broadleaf. If you find yourself battling tough broadleafs in your RR crops, you can always add 2,4-D when spraying corn or Pursuit when spraying soybeans for even better weed control.
When establishing a new plot previously in a cow pasture or CRP, I’ll often times spray a week before planting in the spring after first green up at a higher rate like 2 quarts/acre…and then I’ll spray again 3-5 weeks after planting when weeds and crops are up and growing at the normal 1quart/acre rate. Lastly, on crops that grow shorter (soybeans), you can spray more than once during the growing season if the first spraying didn’t get it done. You’ll run some plants over but the weeds will do way more damage if you let them go….NEVER let weeds grow to maturity and seed out because they will haunt you next year.
Calibrating a Sprayer
In order to get the proper application rate of a herbicide you need to know the rate at which you apply the mixture of herbicide and water in total. The easiest and most accurate way to do this is to fill your sprayer with water only and then spray it on a known acreage. You want your spray to contact all weeds so you need to go at a pace that makes for full coverage. I like to set the pressure going to the nozzles at about 45 psi and use nozzles with a medium mist pattern. I don’t want heavy spray that can run off leaves but I also don’t want the spray to be too light where the mist can blow away. A happy medium where the spray is strong enough to penetrate down but not too heavy that it runs off. Once you have your sprayer set, go out and spray a half-acre or acre with water only and measure how much water you used. For me, with my sprayer set up, I run about 7-8 gallons per acre. Once I know this, it’s easy to get my application rate correctly. If I’m spraying three acres for example, I will fill my sprayer with 24 gallons of water and add 3 quarts of glyphosate. The 24 gallons will cover the three acres applying 1quart/acre of chemical.
When spraying using contact herbicides like Fusilade, 2,4-d, and glyphosate weeds need to be actively growing and not stressed (from drought for example). Contact herbicides also need time once applied before it rains…generally at least an hour or two. In general, young weeds are more easily killed than older weeds. Residual herbicides like Pursuit need moisture in the soil for good activation making them able to work. Residuals need to make contact with the soil for them to be effective …so only use them when the crop to be sprayed is early on when gaps exist for the spray to reach the soil. Spray on calm days so that you reduce or eliminate drift. Don’t spray during periods where heavy dew exists on the plants as the herbicide can run off. One last thing…you might hear or read that adding crop oil, surfactants, or fertilizer solutions to your spray will make it more effective. While I won’t argue that this may be true, I have found that it is usually not necessary and I seldom add any. Follow the safety procedures and pay attention to the cautions on the label instructions.
Learning and knowing how to use the Big 5 herbicides will help you with food plots and habitat improvements. Keeping it simple and following the label instructions with a properly calibrated sprayer will keep weeds at bay. Using glyphosate and RR varieties in your food plots makes for the easiest and most effective weed control for the food plotter.
By the end of May or earliest parts of June each year, I will have sprayed my RR food plots…this year should be no different. June for the deer hunter and manager is about weed control in annual grain crops. It’s a rather tedious but much needed step in successful food plotting.