Hay Bales: Dealing with Johnsongrass in pastures and hay meadows

Mike Trammell - Ag Educator & Multi-county Agronomist, Pottawatomie County OSU Extension Service

Johnsongrass is a non-native warm-season grass that most people love to hate. It grows well in most Oklahoma soils and is an aggressive invader in bermudagrass hay meadows. It was introduced into the United States, possibly from Turkey in 1830, as a pasture grass and to reduce wind erosion in “worn out” fields previously used for crop production, especially after the Civil War. Since that time, it has invaded most of the southern U.S. from coast to coast.

Many producers do not see Johnsongrass as a problem, they tend to look at it as another forage resource. Managed properly Johnsongrass can be a high quality, highly palatable forage. Johnsongrass plants can average 2 to 4 tons of production per acre and can range from 10 to 14 % crude protein. The total digestible nutrients (TDN) when cut properly ranges from 50 to 60 %. When cut and rolled up with bermudagrass it can make a welcomed boost in total hay production, but Johnsongrass does have its own management problems. Nitrate toxicity and prussic acid poisoning are the two most common problems with grazing or using Johnsongrass for hay. Nitrate becomes a problem when hay is cut, or forage is consumed from heavily fertilized pastures that contain Johnsongrass during or after a drought. This is especially true when pastures are fertilized just prior to the harvest of the forage. Cloudy weather, shading by other plants and frost may also increase nitrate levels in Johnsongrass plants. Once nitrate levels reach toxic levels and it is cut for hay, that hay will remain toxic since the nitrate does not degrade over time in the dry forage within the bale.

Prussic acid can also cause toxicity in Johnsongrass forage and is most often associated with problems of animals consuming the Johnsongrass immediately after a killing frost. Though not as common, problems can also arise on new, fast growing Johnsongrass shoots, especially following a period of drought. More mature plants generally have lower levels of the toxin than young, immature plants. Prussic acid, unlike nitrate, will dissipate out of the forage over time and hay dried down to 18 to 20 % is less likely to contain toxic levels of the prussic acid.

Many producers do not want to deal with the headache of trying to manage around the difficulties of these two toxicity issues and we receive many calls on the best methods of ridding bermudagrass stands of this unwanted guest. Probably the cheapest and best method of getting rid of this grass is to manage against it. Johnsongrass, by its nature, cannot withstand constant grazing pressure. After removing the first hay cutting in the spring, turning cattle in on a meadow for the rest of the summer will usually result in the death of the invading Johnsongrass. If grazing of the plants is not an option, then cutting or mowing the meadow on a 25 to 30-day interval will normally kill it out. None of the intervals can be skipped however, or the plants will have an opportunity to rebuild their food supply in the root system and will re-appear the following year.

Chemical control can also be an option although an expensive one. Using a wick applicator to wipe glyphosate on the plants from two directions can be very effective in controlling the plants. The Johnsongrass plants must be given time to grow above the height of the bermudagrass and should only be treated after a rainfall when the Johnsongrass is actively growing.

There are a couple of herbicides labeled for Johnsongrass that that can be applied as a broadcast spray application. These herbicides have added another tool to the toolbox for Johnsongrass control. The first is Outrider herbicide. With this herbicide, applications should be made when the Johnsongrass is actively growing and 18 to 24 inches in height. After the first cutting of hay, once the Johnsongrass has had a chance to grow back, is a good time to utilize this product (consult the label for specific use recommendations). Pastora, a post emergence herbicide, is labeled for control of Johnsongrass (18 inches tall or less) in bermudagrass hay pastures. Another post emergent herbicide, Plateau, is another control option for Johnsongrass in bermudagrass pastures. Again, consult the label for specific use recommendations for each of these herbicides.

As stated previously, Johnsongrass is a plant that many people love to hate. We do have several options for ridding it from bermudagrass stands, but don’t forget that with a little management and care, it can also be a valuable forage resource.

Remember with all herbicides, the label is the law. Follow all label directions.

If you have questions concerning this topic or related topics, please contact the OSU Extension Center at 273-7683, stop by the office, or visit our website: http://www.oces.okstate.edu/pottawatomie/

The pesticide information presented in this publication was current with federal and state regulations at the time of printing. The user is responsible for determining that the intended use is consistent with the label of the product being used. Use pesticides safely. Read and follow label directions. The information given herein is for educational purposes only. Reference to commercial products or trade names is made with the understanding that no discrimination is intended and no endorsement by the Cooperative Extension Service is implied.

Mike Trammell joined the team as the Pottawatomie County agriculture extension educator and multi-county agronomist.