I've had more calls on sandbur control in pastures and hayfields in 2014 than I can ever remember. While it is obviously too late to do anything about them this year, plans can be made for next year. In general, if you had sandbur in a field this year and were unable to control them, there is a good probability they will be back next year.
There are four products that I recommend for sandbur control in pastures and hayfields. For me to recommend a product, it has to meet a few basic qualifications. First, it must be labeled for the crop it is applied to. It is illegal to apply a pesticide to a crop that is not listed on the label. Second, it has to work. In this instance, it has to control a large percentage of the sandbur when correctly applied. Third, it cannot cause undue crop injury when used according to labeled directions.
There are two broad ways to control sandbur. One is with a preemergent herbicide. This type of herbicide must be applied before the sandbur seed germinate. The only labeled preemergent herbicide for sandbur control in pastures and hayfields is Prowl® H2O. It is labeled for bermudagrass and other warm-season grasses when in winter dormancy. In southern Oklahoma and northern Texas, the most common application time is February or very early March before the grasses break dormancy. There is a 60-day haying restriction and a 45-day grazing restriction if Prowl® H2O is used. Good results can be obtained from Prowl® H2O if it is properly incorporated by rainfall or irrigation within 10 to14 days of application. It is a fairly expensive treatment.
The other three products for sandbur control in pastures and hayfields are post-emergent treatments. This means the products must be sprayed onto an emerged sandbur plant. One product is Pastora®. It is only labeled for bermudagrass, so applying it on any other type pasture or hayfield is illegal. It must be applied to very small sandbur, and the spray must contact the sandbur plant. For that reason, the bermudagrass should be grazed or hayed very short. If the bermudagrass is taller than the sandbur plants, it will absorb most of the herbicide and poor control may result. The labeled rate is 1.0 to 1.5 ounces per acre. It costs about $20 per ounce, so make sure your sprayer is properly calibrated so that you know exactly how much you are applying. Keep in mind that Pastora® will control most annual grasses, including crabgrass, seedling johnsongrass and bahiagrass. If annual grasses are an important part of your grazing program, do not use Pastora®. There are no grazing or haying restrictions associated with the use of Pastora®.
The least expensive treatment is Roundup PowerMax® applied immediately after the first hay cutting. It is labeled for use at a rate of 10 ounces per acre on bermudagrass hayfields immediately after the first hay cutting. It will also control many annual grasses other than sandbur. It is important to treat as soon as possible after the first hay cutting for two reasons. First, there will be less crop injury since there will be less bermudagrass leaf area to take up the herbicide. Second, the product must contact the sandbur plants while they are small; this is less likely to happen if the bermudagrass has regrown and is covering the sandbur. There are two things to keep in mind with this product. One is that there is a 28-day hay and grazing restriction after using it in the manner described above. Two is that you can only make one Roundup® application per year to a bermudagrass field. If you used Roundup® in the winter or early spring for winter weed control, it cannot be used after the first hay cutting. Roundup PowerMax® is the least costly treatment available for sandbur control.
The fourth product is one that I recommend with caution. It is imazapic, sold under the trade names Plateau® and Panoramic 2SL. The caution is this product will stunt bermudagrass growth for a period of at least 30 days. Some varieties, such as Jiggs and World Feeder, are more prone to crop injury than others. It is labeled for use in most perennial grass species, including native range. It may damage fescue if applied to that crop. It is an excellent herbicide, with both preemergent and post-emergent activity. I recommend its use in cases where forage growth is less important than controlling sandbur. It is relatively inexpensive and has a wide weed control spectrum. There are no grazing restrictions and a seven-day haying restriction when using imazapic.
In many cases, a producer may treat sandbur in the spring and get excellent control, only to see a new flush of sandbur appear in late summer if good rainfall occurs. Keep in mind that this is not due to control failure, but due to the fact that there is a large supply of seed in the soil that germinate when conditions are good. Do not expect to eradicate sandbur with one application or in a single year.