Livestock producers who plan to graze crop residue or feed weedy alfalfa hay this fall should be aware of the dangers imposed by a particular weed, warns Bruce Anderson, University of Nebraska Extension forage agronomist.

“Black nightshade is common in many corn and soybean fields as well as in new alfalfa,” says Anderson. “It usually isn’t a problem, but if the population gets high it can poison livestock grazing the plant or consuming hay with nightshade in it. Almost all livestock, including cattle, sheep, swine, horses and poultry are susceptible.”

All plant parts contain some of the poison and the concentration increases as plants mature, except in the berries, he says. Drying the weed as hay or waiting until after a freeze won’t reduce the toxicity; neither will fermenting it as silage.

It’s very difficult to determine how much black nightshade is risky. Guidelines say that a 1,000-lb animal that eats 1-3 lbs of fresh black nightshade is at risk of being poisoned. In a stalk or stubble field, a few green nightshade plants might be very tempting to a grazing animal, especially if there is little grain to select. In hay, the nightshade may be sparse through most of the field but in a few areas it could be quite thick. Animals offered hay from those thick areas could be at risk.

“So common sense and good observation must be your guide,” says Anderson. “If they selectively graze green plants in stalk or stubble fields, pull animals out and wait for a hard freeze before trying again. Keep track of bales from heavily infested areas. Either don’t feed these bales or grind and mix them with other feeds to dilute the problem. If still unsure, expose only a few animals at a time to risky feed.

“Just remember, an ounce of prevention is worth a pound of cure,” he adds.