Over the last 10 years, foxtail seems to have taken over many farms in the Southeast. While early in the summer young foxtail is not very evident, in the late summer and early fall, its seedheads are prevalent throughout fields across the South.
When foxtail is young, livestock will consume it, but mature plants and seedheads are not palatable. The sharp awns on the seedheads can injure livestock grazing or consuming infested hay. Foxtail is a group of plants that include annual species, such as yellow (Setaria pumila), green (S. viridis) and giant (S. faberi), as well as perennial species such as knotroot (S. parviflora) (Photo 1).
For all foxtail species, the combination of large seed production and long seed dormancy creates a large seedbank in the soil. Research has shown foxtail seed can remain viable in the soil for 13 to 30 years, dependent on the species. When desirable forages are suppressed by manmade or environmental conditions, seed may germinate quickly and, within a couple of years, can be the dominant species in the pasture or hay field.
The best defense for foxtail, or any weed, is a good offense. Maintaining an overall healthy forage system can reduce the likelihood of weed encroachment in your pasture or hay field. This starts with proper soil fertility. Improved forage species require specific soil nutrients, mainly nitrogen, phosphorus and potassium, and a proper soil pH to be competitive against weeds.
Soil testing pastures every other year and hay fields every year, along with timing fertilizer applications with forage growth curves, allows for optimum growing conditions for your forages. Based on your soil test laboratory results and your local extension service recommendations, it might be beneficial to split applications of some nutrients in order to maximize forage response.
Another important part of the offense is plant management. Grazing management is critical in order to maintain a healthy, productive pasture. Overgrazing is often the result of overstocking livestock, continuous grazing or both. Overgrazing, as well as harsh environmental conditions like drought, open the plant canopy so that patches of soil receive the increased sunlight and temperatures necessary for weed germination and growth.
Overgrazing and droughty conditions also weaken the forage plants, making them less competitive against weeds. In hay fields, make sure you are using the recommended cutting height for your forage species to prevent overstressing the plants. Using proper cutting height, combined with proper soil fertility, promotes a strong, healthy and productive hay field. If you are feeding hay, make sure the hay is not contaminated with foxtail, since much of the foxtail seed distribution occurs through contaminated hay that is then fed in pastures. Foxtail has been especially evident in grazing pastures since the drought of 2016 affected several Southeastern states, resulting in the weakening or demise of many pasture forages.
It is necessary that these fundamental management strategies are practiced before herbicides are considered. The combination of these foxtail control techniques is part of what is known as an integrated pest management program that is usually more successful than relying on herbicides alone. With that said, there are a few herbicide options which have shown some success.
One method of verifying perennial versus annual foxtails is to observe the plant roots. Notice the “knotty” rhizomes on this knotroot foxtail which helps the plant survive from year to year. Photo provided by Leanne Dillard.First, a pre-emergence herbicide like Prowl H2O (pendimethalin) or Rezilon (indaziflam) are options if your fields contain any species other than knotroot, which is perennial. This may be best determined by examining the roots of mature plants (Photo 2).
Either of these products may be applied to established forages during late winter or early spring and must receive rainfall in order to be incorporated into the soil prior to foxtail seed germination (Photo 3).
2.5 fluid ounces per acre Rezilon shows control of yellow foxtail at five-and-a-half months after application in a healthy bermudagrass forage. Photo provided by Leanne Dillard.Field trials have recently shown more promising results with timely applications of Rezilon compared to that of Prowl H2O. Prowl H2O is labeled for use on all established, perennial forage grasses, whereas Rezilon is limited to established warm-season grasses like bermudagrass and bahiagrass.
For post-emergence herbicide options, Pastora (nicosulfuron + metsulfuron) has long been the staple for foxtail control in bermudagrass forage in the Southeast. The longstanding recommendation has been 1.5 ounces Pastora + 8 fluid ounces glyphosate/A (4 pounds per gallon product), followed by 1 ounce Pastora 16 days later (Photo 4).
Shown is an application of 1.5 ounces per acre of Pastora + 8 fluid ounces per acre, followed by 1 ounce per acre Pastora 16 days after initial application. The photo was taken 26 days after initial application. Notice additional damage to the desirable forage. Photo by Dr. David Russell.Even with ideal growing conditions, this has almost always stunted bermudagrass forage and, in many cases, growers have lost a hay harvest. Approximately 70% foxtail suppression was the best-case scenario from this treatment at one to two months after application if the treatment was made prior to foxtail seedhead formation.
Facet L (quinclorac) is another post-emergence option that has both foliar and soil activity on foxtail (Photo 5).
Knotroot foxtail shows herbicide symptoms from 1 quart per acre of Facet L + 1% v/v MSO. The photo was taken 14 days after application. Photo by Dr. David Russell.The level of control is similar to Pastora but with much less bermudagrass and tall fescue injury. Use rates are approximately 12 to 64 fluid ounces per acre. Replicated field trials have shown that using 16 fluid ounces on 3-inch-tall knotroot foxtail has only provided about three to four weeks’ suppression. One quart per acre has provided 60% to 70% control for about three months, and 2 quarts per acre has provided 75% to 80% control for about three months. Good growing conditions, along with vigorous bermudagrass growth and ground coverage, have increased the level of foxtail control while using Facet L.
Our current research continues to explore the effectiveness of other herbicides like Velpar (hexazinone) as well as various combinations of rates, timing, tank mixtures and forage species interactions on foxtail control. These recommendations are location- and species-specific; therefore, it is important to contact your local extension office for more information.
