Livestock producers in the southern United States should not overlook johnsongrass in their pastures. For one thing, under certain conditions it can kill your cattle. Another reason not to overlook johnsongrass is that it is excellent forage – if you can get over the fact that it can kill your cattle!
Positive Aspects of Johnsongrass
As far as nutritive value is concerned, johnsongrass is tough to beat. One study conducted at the Noble Research Institute in Oklahoma showed that the quality, expressed as percent crude protein (% CP), and digestibility, expressed as percent total digestible nutrients (% TDN), of johnsongrass is as good as any of the forages tested (Figure 1). In this study, bermudagrass was neck and neck with johnsongrass in terms of % CP and % TDN. The bermudagrass was a managed stand and was fertilized with 50 to 100 pounds per acre of actual nitrogen. The johnsongrass was unfertilized and unmanaged.
In another Noble Research Institute study, the palatability of several warm-season grasses was evaluated by yearling steers. In the study, three yearling steers had access to plots containing pure stands of 14 different warm-season perennial grasses (both native and introduced).
Johnsongrass came out near the top in this study. Alamo switchgrass was the only other grass in the study that had more bites taken of it than johnsongrass in year one (9,262 versus 6,062, respectively). A testament to the preference for johnsongrass by livestock can be seen while driving down the road; pastures that are continually grazed generally won’t have any johnsongrass, but you will see it all along the roadside – out of reach of the fenced-in cattle.
Negative Aspects of Johnsongrass
Johnsongrass is on the noxious weed list in several U.S. states (including Kentucky) and has even made the list of the 10 most noxious weeds in the world. Johnsongrass can accumulate nitrates during the summer if exposed to several dry, cloudy days in a row. It can also produce prussic acid (hydrogen cyanide) after stressful conditions such as drought, freezing weather or exposure to a herbicide that kills grasses. If your johnsongrass is subjected to any of these conditions, keep cattle away for about a week to allow the prussic acid to dissipate. ~ Chan Glidewell, Noble Research Institute