Eastern black nightshade is an annual. It grows year to year from seed. Any weed that has a large population can cause pressure in a plant system because it competes with the crop for resources such as sunlight and nutrients.
Based on an informal survey I conducted of county educators in horti-culture, nightshade was a nuisance for growers of peppers, tomatoes, pumpkins, and a few other crops. It can be a serious problem for some vegetable growers. On tomatoes for example, it is hard to control because there are very few products that have activity on nightshade.
We can thank or blame the northern climate for the fact that not many central European plants thrive here, or are rare. Black nightshade is a dangerous poisonous plant further south – its nature is well described by its shadowy name, which refers to the fact that the plant has been seen as an ally of death and darkness, and the witches that serve them. Further south it is a common weed, but in Finland it grows mainly in the south of the country, on rich warm ground in gardens, on wasteground and in fields, usually in places that have been disturbed by humans. In the most southerly parts of Finland this annual plant is only able to ripen its seeds in good summers, and the first night frosts often cut down plants which could still be flowering in October. Elsewhere in Europe black nightshade has been used as folk medicine: the fresh leaves were pounded into a mass and used externally to treat infections and weeping wounds. Nightshades’ alkaloids, especially solanine, are also common ingredients in modern medicine. There is even literature that says that berries or leaves may be eaten, but this information is not to be trusted.