Controlling Sandburs
Sandburs are a common weed issue found in pastures, forage crops, and lawns. As the name implies, sandburs are typically more of an issue in sandy soils. They are an annual warm season grass, but with a mild winter can behave as a short-lived perennial. Seeds can germinate all summer, but most will germinate in May and June. Sandburs can obviously be an issue with livestock in pastures and hay production but can also reduce forage quality and quantity. Since sandbur seeds can stay viable in the soil for 5 to 8 years, the main objective for suppression would be reducing seed development. Control will take several years of intensive management utilizing both cultural practices and herbicides.
Proper weed management starts with taking care of the soil, which starts with taking a soil sample. To give the desired crops a completive edge, soil pH and nutrient deficiencies will need to be corrected and maintained. Sandburs are more tolerant of acidic (low pH) soils than many warm season forages. Applying adequate nitrogen will be the most beneficial to improve the stand of the desired forage. Correcting phosphorus and potassium will also help improve root development and plant regrowth. In addition to soil fertilization, other cultural suppression practices include managing stocking rates and prescribed burning. Proper stocking rates should be managed to retain adequate biomass for the crop to regrow at a faster pace and stay completive with sandburs. For Bermudagrass, leaving 2 to 3 inches is essential for good regrowth for both haying and grazing.
Prescribed burning can reduce sandbur seed production if executed at the right time and with high intensity. Fall burns will likely be better, unless there is sufficient fuel (old growth) for a hot spring burn. If the fire from the burn is not hot enough, it may actually stimulate germination. At first one would think that would be a bad thing. After the light burn a higher percentage will emerge the first year, which an herbicide would effectively control a larger percentage of the sandbur population in one application. There are a few herbicides that can be used to assist in sandbur control. Unfortunately, most are only labeled in bermudagrass. There are no herbicides labeled for sandbur control in Old World Bluestem, crabgrass, and some native grasses. In most native grass pastures, herbicides with the active ingredient imazepic (Plateau, Panoramic, or Impose) will provide some control but will also cause some crop injury to the native grasses. This injury is often temporary and lessened if good growing conditions follow herbicide application.
For bermudagrass, the use of a preemergence (applied before sandburs germinate) herbicide like pendimethalin (Prowl H2O) will help reduce half to two-thirds of the largest and earliest flush of sandburs. A newer product now available, called Rezilon, gives farmers another preemergent herbicide option. It is recommended to be applied well before sandbur germination. If sandburs have already emerged this product will not provide any control. Ideally it should be applied late-winter but can also be applied mid-season generally after the first cutting to prevent late-season sandbur emergence. The first application of Rezilon needs to be applied by February. It can control and suppress weeds for up to 4 months, so depending on when the first application was made a second application might be needed in June or July. A rainfall event or irrigation of at least a half of an inch is needed to move the product from the soil surface to the sandbur seeds in the soil. For most effective control, a water incorporation needs to occur within three weeks.
If applying Rezilon after sandbur emergence or if there are perennial sandbur plants found, tank-mixing a postemergence product like glyphosate might be needed. Add Rezilon to the sprayer prior to adding the glyphosate to prevent tank-mix issues or reduced weed control. Rezilon is a suspension concentrate product that needs constant agitation in the sprayer to keep it in solution. Rezilon doesn’t have any grazing restrictions, but grazing after an application and prior to incorporating rain can reduce weed control. There is not a haying restriction when applied at 3 ounces per acre. There is a 40-day haying restriction if more than 3 ounces are applied.
Postemergence (applied after bermudagrass and sandburs are actively growing) herbicide options include glyphosate (Roundup Weathermax), imazepic (Plateau), or nicosulfuron with metsulfuron (Pastura). Read and follow label directions for rates, application timings, and surfactants to limit crop injury and to achieve satisfactory sandbur control. Lack of control is usually due to herbicide application timing. Sandbur growth stage is critical for some products. For instance, after sandburs reach 1.5 inches tall the expected control will be reduced with products like Pastora. If applied correctly, over 90 percent of the sandburs can be controlled with the postemergence herbicides. Keep in mind, sandburs will continue to emerge as the season progresses which may make it appear like the early herbicide application failed.
Herbicide products like MSMA are good options for cotton fields, golf courses, sod farms, and highway right-of-ways, but cannot be legally applied to lawns, pastures or hay ground. This is mostly due to the risk of animal poisoning from being an arsenic-based herbicide. A multi-year strategy of combining cultural suppression practices and herbicides is necessary. For more information refer to OSU factsheet PSS-2596 Sandbur Control in Bermudagrass Pastures or visit your local OSU Murray County Extension office.
