Eastern Black Nightshade:
"Biology and Management"

Eastern black nightshade is one of those weeds that are definitely not welcomed in Ontario fields and there are many reasons for this. Not only will it rob crops of nutrients and moisture, but it is also toxic and it can slow down harvest. As if those reasons weren't bad enough, there are now some populations of this weed which are resistant to the group 2 class of herbicides (i.e. Pursuit). This means that those resistant populations will survive applications of group 2 herbicides that are normally very effective on this weed.

Biology and origin of eastern black nightshade

A member of the solanaceae family, and close relative of tomatoes and potatoes, eastern black nightshade (Solanum ptycanthum Dun.) is native to North America and is widespread in eastern Canada. Eastern black nightshade has occurred as a ruderal weed in Ontario since the mid 1850s. It began to invade cultivated fields in the early 1960s when the introduction of selective herbicides eliminated other more competitive weed species.

Eastern black nightshade is an annual, rarely a short-lived perennial. Stems are green or greenish purple, round or angular. Seedling leaves are usually purple underneath. Berries are 5 to 9 mm in diameter and contain up to 100 seeds each. It is therefore very prolific, as a single plant can easily produce up to 1000 berries (Figure 1). Pictures were adapted from the Michigan State University website and the United States Department of Agriculture website.

Figure 1. Morphology of berries (A), flower clusters (B), seed (C),
and seedling (D) of Eastern black nightshade.

Problems

• Eastern black nightshade is found in many crops and is a particular concern for soybeans, edible beans and pea growers.
• This weed can cause substantial yield reduction, but harvest problems and reduced crop quality are probably of greater importance, even at low levels of infestation.
• Foliage and berries will plug combines and stain the harvested soybeans or act as a source of moisture for fungal growth during storage.
  

Nightshades are poisonous plants

All parts of eastern black nightshade are reputed to be poisonous; however, the green leaves, stems, and seeds are especially toxic. Following dry conditions, the concentration of the toxins is higher in all plant parts; toxicity also varies according to plant stage. The ripe fruit may be relatively nontoxic, while the green fruit may be quite poisonous. The toxic properties, which include tophane and steroidal alkaloids, are heat stable and will remain poisonous even when stored with forages. As a result, producers must be cautious about nightshade-contaminated hay. Feeding experiments have demonstrated that this plant can be toxic to cattle if it comprises about 25% or more of the forage intake. Commonly induced symptoms in farm animals include colic, diarrhea, salivation, and vomiting.

In the case of humans, although nightshades are considered to be poisonous by many authors, there is considerable conflicting evidence in the literature and indeed some authors have stated that nightshades are non-poisonous (Bassett, I. J. and D. B. Munro. 1985. Can. J. Plant Sci. 65: 401-414). Until more information is available, it is not advisable to eat these otherwise attractive berries.

Management of eastern black nightshade

This species is easily controlled by a range of herbicides. Atrazine (Atrazine/Aatrex), bromoxynil (Pardner/Koril), and dicamba (Banvel II/Vanquish) are very good options in corn. In legume crops, imazethapyr (Pursuit) and fomesafen (Reflex) will provide good to excellent control. Glyphosate products are also effective options in Roundup Ready crops.

However, since eastern black nightshade will germinate over an extended period of time, non-residual herbicides will often provide less satisfactory control after the initial flush has been eliminated. In crops that are less competitive or that take longer to close canopy, residual herbicides represent a good choice. The chloroacetamide herbicides (Dual, Frontier, Axiom) have excellent residual activity against eastern black nightshade. Ketone herbicides such as isoxaflutole (in Converge) or the recently introduced mesotrione (Callisto) also have residual activity in corn.

Related Links

• Michigan State University
• United States Department of Agriculture

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