By William Curran
This is the time of year where we often find Eastern black nightshade in some of our crops. This annual species (Solanum ptycantum) is native to the Americas and can be found in field crops and especially soybean and also forages like alfalfa. Although it can compete and reduce yield, it is more of a problem at harvest and influencing crop quality. At soybean harvest time, the nightshade foliage is green and the berries are still intact and usually dark purple (see accompanying image). The berry juice stains the grain, increases grain moisture and the potential for molds and can clog and gum up combines.
Eastern black nightshade is toxic as are most plants in the nightshade family. All parts of the plant are considered poisonous; however the green leaves, stems, and immature seeds are especially toxic. The green fruit is also poisonous, while the ripe fruit is reported to be relatively nontoxic. The concentrations of the toxins are higher following dry conditions. The toxicity is not removed by drying and they are also relatively heat stable, although some references report that toxicity is lost by cooking. Portions of green plant material stored with forage will remain poisonous, so producers should be cautious when feeding livestock nightshade-contaminated hay or silage. The toxicity of the green plant material varies from 0.1 to 1% of an animal’s body weight (1 - 10 lb nightshade/1000 lb animal - we are not sure if this is fresh or dry weight, which would make a big difference). Clinical signs of poisoning develop rapidly and most animals will succumb or recover within 24 to 48 hours. Limited therapies are available for treatment.
Eastern black nightshade is generally manageable in corn mostly due to available herbicides. In soybean, this weed tends to be tolerant to glyphosate, so it can be a problem in Roundup ReadyTM (RR) soybeans. In non-RR soybean, the group 2 herbicides (ALS-inhibitors) and particularly the sulfonylurea’s like chlorimuron and thifensulfuron are notorious for their inactivity. The Group 14, or PPO’s, are often the products of choice for control, but they are only effective on younger plants and not plants that are flowering or already have fruit. This is one weed where a harvest aid is often considered and Gramoxone or paraquat is usually the product of choice. A thick well-managed alfalfa crop is usually quite effective at suppressing Eastern black nightshade, but new seedings or older stands can be invaded. Herbicide choices in alfalfa are limited to products like Pursuit or Raptor, which are only fair, or possibly with in-between cutting treatments. Older stands should probably be rotated back to corn.
Mature Eastern black nightshade berries (Image by W. Curran).
Source:psu.edu