The Importance of Identifying Food Plot Weeds and Matching Herbicides to Your Plantings

By Bradley Williams, QDMA Certified Deer Steward

Many wildlife managers overlook the important step of identifying the problem weeds in their food plots and fields. These weeds need to be identified so that the following questions can be answered. What type of plants are my problem weeds? Are these weeds providing a benefit to the wildlife? What type of herbicide can I use to control them if needed? What forages can I plant that will allow me to selectively control the weeds without killing the food plot?

Weeds can be simplified on a basic level into the categories of either grass or broad leaf weeds. Once the category of the problem weed is identified, it is important to know if the weed is even necessary to control. Many plants considered to be “weeds” often provide value to the wildlife being managed. “Weeds” such ragweed, begger lice, old field aster, blackberry, partridge pea, tropic croton and many other “weeds” are highly selected food sources for whitetail, turkey, and quail. If these weeds are in your food plot, I would consider them a welcome bonus instead of a “weed.” Species that provide little or no food value to wildlife that can quickly out compete planted forages, such as fescue grass, orchard grass, crabgrass, curly dock, sericea lespedeza, purple dead nettle, ragwort and many others should be eliminated from food plots with proper herbicide treatment.

Various types of selective herbicides can be used to control weeds in one category without harming your food plot if the proper mixture is planted. If the predominant weeds in your food plots are grasses, a grass selective herbicide such as Clethodim or Sethoxydim can be applied for weed control. Broadleaf weeds can be controlled with one or a combination of many broad leaf herbicides such as 2,4D, Clopyralid, or 2,4DB without harming the food plot depending on what forage is planted. Some broad-spectrum herbicides such as Glyphosate and Imazethapyr can also be applied at the proper time to certain forages to control both types of weeds at the same time.

Food plot seed mixtures should be carefully evaluated and compared to the type of problem weeds that need to be controlled. For example, if warm season grasses are a problem in your warm season food plot, consider a broadleaf mixture that does not contain a grain or grass so that a grass selective herbicide can be applied. A good option for a warm season planting in this situation would be a cowpea and sunflower mixture or soybeans. A grass selective herbicide could then be applied post emergence to kill the problem grasses without damaging the food plot. Many commercial warm season food plot mixtures include grains such as grain sorghum, millet or Egyptian wheat. Using a grass selective herbicide to control the grass weeds would kill the grains in the mixture. Corn is also in the grass family and would be killed by most grass selective herbicides. If warm season broadleaf weeds are a problem in your plots, and a warm season legume is what you would like to plant, soybeans can be planted alone. The 2,4DB could then be applied for broadleaf weed control. If both broadleaf and grass weeds are a problem, consider a forage that is compatible with a broad-spectrum herbicide. Imazethapyr is a broad-spectrum herbicide that can be applied pre or post emergence to cowpeas, winter peas, soybeans, and post emergence to clovers and alfalfa.  Glyphosate can also be used on Roundup® ready varieties of corn and soybeans to control both types of weeds. Glyphosate can be applied to a plot two weeks prior to tillage to help kill existing weeds. Glyphosate is typically not soil residual. The two weeks wait time is to ensure the weeds are killed to the root prior to tillage. The two-week wait is not needed if using a no-till drill.  It is important to consider the time an herbicide remains soil residual and how it may impact future plantings. This is often referred to as crop rotation minimum and is usually expressed in number of months.

In cool season plots where grasses such as fescue are problematic, planting a cool season broadleaf mixture such as clovers or brassicas are good options to allow the application of a grass selective herbicide. Wheat, rye, or oats included in the mix would be killed by the grass selective herbicide used to control the fescue. If deer density and grazing pressure is high, it may be necessary to include wheat, oats, or cereal rye to buffer gazing pressure on the slower establishing clover or brassicas. These grains will be killed by the grass selective herbicide, but so will the fescue. This will help promote successful establishment of the remaining forages. If a cool season broadleaf weed such as purple deadnettle is a problem, cool season grain stands such as wheat and oats can be planted to allow the application of a broadleaf selective herbicide such as Dicamba. These grain-only plantings allow for the use of a broad range of herbicides to control weeds. Make sure to always check the herbicide label to verify it will control the target weeds and not damage the food plot. For example, purple deadnettle may not be controlled by 2,4D or 2,4DB even though it is a broadleaf weed. Dicamba, however, should be successful in controlling the deadnettle.  2,4DB can be applied to clover and alfalfa plots to control several types of broadleaf weeds without harming the alfalfa and clovers, but it may harm brassicas contained in the mix. Brassicas can be treated with certain types of broadleaf selective herbicides such as Clopyralid, but any clover included in the plot may be killed. Planting food plots with seeds from the same plant family instead of diversified mixtures will make herbicide selection easier in plots where difficult weeds have become out of control.

There are many great commercial food plot mixtures available that produce high quality food plots. Many of these are money well spent. However, before buying a commercial mixture it is important to know what plants are contained in the mixture and what the problem weeds are where you plan to plant. Many commercial blends contain such a diverse seed mix they eliminate herbicide use all together. The blends that include multiple varieties of grains, brassicas, and legumes all mixed together make it extremely difficult if not impossible to find an herbicide that will control the problem weeds without killing a part of the seed mixture. Matching herbicide, weeds, and forage plantings together can be a complicated process. This is why it is important for a land manger to be able to identify weeds, and at least be familiar with a few herbicides that can be found at your local agriculture supply store. If you are not comfortable with weed identification, are unsure of what herbicides to use, or what forages compliment them, your local extension office or private consultant should be able to help.  It is the law and extremely important to use all herbicides only as directed by the product label. The main take away from this article should not be a guide to herbicide use, but an emphasis on the need to identify weeds and select food plot seed mixtures accordingly. Don’t let your ego and product marketing trick you into buying the latest and greatest “super mixture.” It may not establish successfully if it doesn’t complement your weed control efforts and abilities. For success, keep food plots simple and straightforward to manage.