Illus. Weeds of the North Central States
Bitter nightshade, also called climbing nightshade (Solanum dulcamara) is commonly found throughout Minnesota growing along fencerows, alleyways, in hedges, and other waste places. It's a perennial woody vine with little star-shaped purple flowers and green berries that turn red when ripe. Bitter night-shade spreads by seed, but its stem can also root as it creeps along the ground.
Bitter nightshade is sometimes called deadly nightshade, but that name implies a greater threat than the plant actually poses. It is mildly poisonous, however; the toxic substance, solanine, is most concentrated in the unripe berries. Cases of illness resulting from eating its green berries have been reported. The greatest potential danger is for small children, because of their lower body weight.
Due to potential problems associated with nightshade and the fact that it is not a particularly desirable plant in the landscape, it is best to eliminate it. If you have only a few plants, you may want to simply dig them out. To do this, locate the main stem of each nightshade plant and dig down around it to remove as much of the root system as possible. If you see new plants sprouting after digging out the original, remove them as soon as you see them.
A non-selective herbicide containing glyphosate (Ortho Kleenup or Monsanto Roundup, among others) will also provide good control. When using glyphosate be sure to cover the plant thoroughly with the herbicide, but don't soak the soil. Glyphosate will damage or kill almost any green, living plant tissue it contacts, so be careful to avoid surrounding vegetation, if possible. Wipe, mop, or spray the chemical directly on the nightshade.
Apply glyphosate when the wind is calm and temperatures are in the 60-80 degree range, and no rain is expected for at least 24 hours. Yellowing and wilting should start within 3-10 days after applying the herbicide. It may take several applications, 10-14 days apart, to complete the job.
Other herbicides labeled for use on unwanted woody weeds include 2,4-D and triclopyr. These ingredients may be in products called brush killers. These also are absorbed through green plant tissue. They can be applied the same way as glyphosate. One difference between them and glyphosate is their selectivity--they are much less damaging to grass. Another difference is that they persist longer in the soil. As with any pesticide, read and follow label directions carefully.