For stocker operators in the Southern Plains and into the Midwest, johnsongrass can be a mixed blessing. Under certain conditions, notes Noble Foundation ag consultant Chad Glidwell, it can kill your cattle. But on the bright side, Glidwell says, “it is excellent forage — if you can get over the fact that it can kill your cattle!”

Researchers at the Noble Foundation have conducted several studies evaluating johnsongrass as forage, finding it can hold up well in terms of nutritional value and cattle preferences. In a multi-season forage study from 1999 through 2001, johnsongrass averaged 11.6 percent crude protein and 58 percent total digestible nutrients. Among 16 grasses included in the trial, johnsongrass ranked first for CP and second for TDN, slighty lower than burmudagrass.

Beginning last year, Noble Foundation specialists engaged in another study evaluating the palatability of several warm-season grasses by carefully observing what steers on pasture actually eat. Yearling steers in this trial have access to plots containing pure stands of 14 different warm-season perennial grasses. Researchers watch each steer and record each bite it takes of each forage type during morning grazing.

Over the summer of 2007 in this test, johnsongrass ranked near the top in cattle preference. The steers took the most bites from the plot of Alamo switchgrass, at 9,262, with johnsongrass second at just over 6,000 bites. Preliminary results from the first grazing cycle this summer show johnsongrass again running second, this time slightly behind burmudagrass.

Glidwell also notes that casual observation also illustrates the palatability of johnsongrass. While the grass is common and abundant along roadsides outside the reach of fenced cattle, it can be hard to find any inside the fences.

But for all its positive attributes as a forage, Glidwell points out that johnsongrass is listed as a noxious weed in several U.S. states, and can be toxic to cattle. Johnsongrass can accumulate nitrates during the summer if exposed to several dry, cloudy days in a row. Under stress caused by drought, frost or herbicide exposure, johnsongrass can produce prussic acid, or hydrogen cyanide. Glidwell recommends that producers watch for these conditions and keep cattle away from any suspect stands of johnsongrass for a week or so to allow the toxins to dissipate. For more information, including resources related to nitrates and prussic acid toxicity, click here.