Comments: Black nightshade is a summer annual, dying off with frosts in late autumn. As with fathen and redroot, it can grow tall and leafy, creating lots of competition with crop plants for light. Black nightshade is often confused with deadly nightshade (Atropa bella-donna), which is a much more poisonous weed than black nightshade, and also much less common, being found only occasionally near Christchurch. The berries produced by black nightshade are often eaten by birds, and the seeds are thus spread in bird droppings. Apart from problems with competition, black nightshade is a problem in pea crops as the berries are hard to separate from peas as harvest time.
Distinguishing Features: Tall, upright plant. Foliage, and especially stems, can get quite a purplish tinge, which is more noticeable late in the season when stressed. The main distinguishing feature is the bunches of berries that form on mature plants. Berries are usually either green or black. Black nightshade also has flowers which are usually white.
Control: Generally controlled by cultivation and most herbicides. However it is resistant to some groups of herbicides. It is resistant to chlorsulfuron (Glean) used in cereals, so a second herbicide often needs to be applied to allow for this. It is not controlled by trifluralin or closely related chemicals. Black nightshade often builds up in orchards, and we suspect this may be due to resistance developing to triazine herbicides like simazine when they are used season after season, and it is also hard to kill with glyphosate once it grows up into lower branches of trees. In recent research at Massey University, we have confirmed that black nightshade taken from an arable cropping paddock in Manawatu was resistant to triazine herbicides used in peas and maize such as cyanazine (eg Bladex), terbuthylazine (eg Gardoprim) and atrazine (eg Gesaprim). The resistant plants tolerated over 30 times higher rates of herbicide than ordinary black nightshade. If this resistance does develop, the weed can still be controlled in peas using herbicides such as MCPB and bentazone. In maize, dicamba can be used to kill resistant plants. For more details on this research, click here.