Annual Grass Nuisances in Bermuda Pastures
Bermuda can be very competitive if managed properly. Correcting soil pH and nutrient deficiencies according to a soil test is a top priority. For Bermuda, nitrogen management is always going to be of main focus, but phosphorous and potassium can also be very beneficial. Other cultural weed suppression practices include proper stocking rate and prescribed burning. Leaving 2 to 3 inches is essential for good regrowth for both haying and grazing Bermuda.
Annual foxtails can occasionally become issues. Both green and yellow foxtail are listed on the Pastura herbicide label, but when applied alone it may only provide suppression. The Pastura label does recommend tank mixing a glyphosate product to improve foxtail control. Depending on the concentration of the glyphosate product being used the use rate would be 3.5-6 oz/acre (5.5 lb/gallon) or 5-8 oz/ acre (4 lb/gallon). While Bermuda is known to fully recover from low rates of glyphosate, temporary yellowing and/or stunting may occur.
Prairie threeawn (aka wiregrass, ticklegrass, old-wild threeawn) is an annual warm season grass weed. It usually encroaches into Bermuda in less productive soils and over-grazed pastures. Correcting soil phosphorous levels is as important if not more important than nitrogen. Fall prescribed burning has shown to be very effective as shown by some field trials conducted by Kansas State University. Burning in November was effective because the seeds were still attached to the stems and were more easily consumed by the fire.
Field trials conducted by OSU showed good efficacy on threeawn when a tank-mix of Pastora and low rate of glyphosate was applied. Pastora didn’t add much to the control, but its label allows for the glyphosate to be legally applied when tank mixed. Glyphosate is no longer labeled to be applied by itself. Some Bermuda injury will be expected but the stand should eventually recover with good growing conditions. These field trials also showed that if soil fertility wasn’t corrected, threeawn repopulated very quickly. More recent OSU field work has shown that adding some Urea Ammonium Nitrate (UAN) can increase control as well as improve the bermuda recovery. Ongoing research is being conducted to fine tune the nitrogen rates.
Sandburs are another annual warm season grass and is often found in sandy acidic (low pH) soils. Correcting soil pH and applying adequate nitrogen will be the most beneficial to improve the stand of the bermuda. Pasture burning can reduce sandbur seed production if executed at the right time and intensity. Fall burns will likely be better, unless there is sufficient fuel for a hot spring burn. If the fire from the burn is not hot enough, it may actually stimulate germination which can be beneficial if followed by an herbicide program.
Use of a preemergence herbicide (applied before sandburs germinate) like pendimethalin (Prowl H2O) will help reduce half to two-thirds of the largest and early flush of sandburs. Pendimethalin can be applied when the Bermuda is dormant and in season between hay cuttings.
The relatively new product Rezilon is another preemergence herbicide that provides control of sandburs, as well as other annual grasses and some broadleaves. It needs to be applied prior to seed germination of the sandburs to work. Late winter applications are recommended from late December through mid-February followed be another application mid-season. If the late winter application is applied too late the first flush and main flush of sandburs will be missed, but Rezilon could still be an option after the first cutting before another flush of sandburs germinates.
Postemergence herbicide (applied after bermudagrass and sandburs are actively growing) 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 control will be reduced with products like Pastora. If applied correctly, over 90 percent of the sandburs can be controlled with the post-emergence herbicides. Keep in mind, sandburs will continue to emerge as the season progresses which may make it appear like the early herbicide application failed.
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 Extension office.
