American black nightshade [Solanum americanum Mill.][SOLAM] Photographs

Black nightshade [Solanum nigrum L.][SOLNI] Photographs

Hairy nightshade [Solanum sarrachoides Sendtner][SOLSA] Photographs

Heartleaf nightshade [Solanum cardiophyllum Lindl.][Bayer code:none][CDFA list:A] (see Similar Species) Photographs Map of Distribution

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SYNONYMS: Complete synonymy is complex and beyond the scope of this publication.

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GENERAL DESCRIPTION: Non-prickly nightshades with simple hairs and white flowers (rarely purplish). These nightshades are members of a difficult complex of widespread, closely related species and varieties for which there remains much taxonomic confusion. Species are similar yet highly variable, making identification difficult. There is also much confusion regarding plant toxicity. Fresh and dried plant material contains variable quantities of several glycoalkaloids, including solanine, and can be toxic to people and livestock when ingested. However, the degree to which plants may be toxic varies according to plant population, maturity, and environmental conditions. Seedlings and ripe berries are usually less toxic than mature foliage and green berries. Poisoning symptoms are similar to those described for horsenettle and related species. Plants also contain salasodine, a steroid compound used to manufacture steroid hormones in some countries. Nightshades are troublesome in many crop fields. They can harbor crop pests and diseases, especially those of tomatoes, potatoes, and peppers. Nightshade berries are extremely difficult to separate from peas and certain beans, decreasing crop value. At harvest, mature plants can form a sticky mass that clogs harvest machinery. Some nightshade biotypes are resistant to certain herbicides.

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MATURE PLANT: Stems of perennial plants +/- weakly woody at the base. Leaves alternate, ovate, variable, with entire to wavy or irregularly shallow-toothed margins.

ROOTS and UNDERGROUND STRUCTURES: Taprooted, with numerous fine lateral roots, or roots fibrous. Plants can develop mycorrhizal associations.

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FLOWERS: Flower clusters raceme-like, sometimes +/- umbel-like in American and hairy nightshade. Corollas star-shaped, 4-12 mm diameter, usually white with pairs of greenish-yellow spots at the base, deeply 5-lobed, fused into a short tube near the base. Lobes greater than length of fused part, often reflexed backwards. Anthers 5, 1.4-2.2 mm long, erect around style. Self-pollinated or out-crossing.

FRUITS and SEEDS: Berries mostly 5-8 mm diameter, often contain sclerotic granules (hard aggregates of stone cells). Seeds ovate, flattened, minutely reticulate-pitted.

HABITAT: Disturbed areas, fields, waste places, roadsides, pastures, annual and perennial crops, especially those that are irrigated, orchards, vineyards, gardens, yards. Plants grow best on fertile, moist soils, but tolerate dry, gravelly or sandy soils. American black nightshade and black nightshade often grow in shady and/or moist places.

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PROPAGATION/PHENOLOGY: Reproduce by seed. Seeds often survive ingestion by animals and can disperse to greater distances with birds and mammals. Berries also disperse with human activity and flowing water. Seed production is prolific. Berries contain numerous seeds, and plants often produce 50-100 berries or more. Seeds are typically highly viable. Fluctuating temperatures in the range of ~ 20-30º C (68-95º F) and light appear to stimulate germination. Most seed germinates spring through summer, but some fall germination can occur in mild climates. Soil disturbance increases the quantity of nightshade seeds in the soil seed bank and seedling emergence.

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MANAGEMENT FAVORING/DISCOURAGING SURVIVAL: Hand-pulling, mowing, and cultivation to prevent seed production for several years reduces the soil seed bank and can eliminate infestations.

SIMILAR SPECIES: Other less common introduced nightshades include South American black nightshade [Solanum furcatum Dunal.][Bayer code: none], bittersweet nightshade [Solanum dulcamara L.][SOLDU], cutleaf nightshade [Solanum triflorum Nutt.][SOLTR], and heartleaf nightshade [Solanum cardiophyllum L.][Bayer code: none][CDFA list: A]. All but South American black nightshade have some deeply lobed leaves. Refer to the table Comparison of nightshades (Solanum spp.): without prickles and with simple hairs for other distinguishing characteristics. South American black nightshade (2n = 72) closely resembles American and black nightshade, but differs by having larger anthers and flowers, the largest flower clusters clearly forked into 2 umbel-like clusters, and 10 or more sclerotic granules per fruit. It grows in disturbed places along the North and Central Coast and in the San Francisco Bay region to 200 m (650 ft). Introduced from South America. Bittersweet nightshade is an ornamental that has escaped cultivation. It occurs on moist disturbed sites and in marshes in the San Francisco Bay region, Central Coast, and Modoc Plateau, to 1000 m (3300 ft). Introduced from Eurasia. Cutleaf nightshade primarily occurs in dry shrublands and juniper woodlands of the eastern slope of the southern Sierra Nevada, Great Basin, northern Mojave Desert, and South Coast region, to 2300 m (7500 ft). Introduced from South America. Heartleaf nightshade is a wild potato with underground stolons and small edible tubers native to Mexico. A single population now eradicated occurred near Davis in Yolo County. Currently, no other populations are known to exist in California. In addition, Douglas nightshade (Solanum douglasii Dunal) is a bushy perennial or sub-shrub that closely resembles American black nightshade, black nightshade, and South American black nightshade. Douglas nightshade is a native species and is a desirable component of natural communities. Only Douglas nightshade has all of the following characteristics: flower clusters umbel-like but not clearly forked, anthers 2.5-4 mm long, white corollas with green spots at the base, and striaght calyx lobes (not reflexed backwards). Also, berries are persistent and have less than 10 sclerotic granules per fruit, and seeds are 1.2-1.5 mm long. Douglas nightshade inhabits dry shrublands and woodlands throughout Southern California (except Sonoran Desert), Tehachapi Mountains, South Coast Ranges, Central Coast, San Francisco Bay region, and southern North Coast, to 1000 m (3300 ft).

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Prevention: There are six species in the Solanaceae considered noxious in California. They are all deeply rooted perennials with an aggressive growth habit in both cultivated and relatively undisturbed areas. All are thought to be native to the southwestern United States and Mexico, except Solanum marginatum, which is native to Ethiopia. There are numerous concerns regarding invasion and spread of these species in California, as they impact agriculture, range, and wildlands. They may reduce crop yields through direct competition for resources. There are also indications of allelopathic effects by S. elagnifolium on several important crops. The foliage and berries of at least S. carolinense, S. dimidiatum, and S. elagnifolium are toxic to livestock. Finally, many of these species are alternate hosts for disease and insect pests in a broad range of crops in California. Known infestations should be aggressively controlled to prevent the further spread of these noxious plants. Information on the following Solanaceae species in Table 1 is given.

Table 1. Solanaceae species considered noxious in California

Scientific name Common name CDFA rating
Solanum cardiophyllum Heartleaf nightshade A
Solanum carolinense Carolina horsenettle B
Solanum dimidiatum Torrey's nightshade A
Solanum elaeagnifolium Silverleaf nightshade B
Solanum lanceolatum Lanceleaf nightshade B
Solanum marginatum White-margined nightshade B

All of these species can spread by seed or root fragments; or tuber fragments in the case of S. cardiophyllum, which is a wild relative of potato (S. tuberosum). Seed may be spread through tillage or harvesting equipment, by animals, or in contaminated hay. Clean equipment before leaving contaminated fields, and avoid spreading root fragments by cultivation equipment. Check hay for nightshade berries, before feeding to cattle. This will prevent livestock poisoning and the introduction of seed into uninfested areas.

Mechanical: All of these species are deep-rooted perennials and may vegetatively reproduce from rootstocks. There is some variation between species in their ability to regenerate from rootstocks; with silverleaf nightshade regenerating from root cuttings <1 cm in length, Carolina horsenettle >1cm, and Torrey's nightshade >2cm. Information is lacking for the other species. Regardless, tillage may spread rootstocks to new areas, where establishment can occur. Small infestations may be hand pulled or hoed, but must be repeated several times during the growing season. Several of these species have sharp spines and gloves should be used for hand pulling. Any root material that is dug should be collected, dried and burned. Repeated mowing throughout the summer may nearly eliminate seed production. However, the plants will take on a flat, rosette-like growth form that is capable of replenishing root carbohydrate reserves.

Biological: There are no currently registered biocontrol agents for use on any of these weeds. There is a great deal of concern since several other species in the Solanaceae family are important agricultural crops in California, such as potato, tomato, eggplant, and peppers. However, researchers have examined a nematode, Orrina phyllobia, which is host specific for silverleaf nightshade. Augmentative releases of this nematode may eventually help reduce silverleaf nightshade populations.
Livestock will favor these spiny plants by overgrazing the surrounding palatable vegetation. If the seed are ingested by livestock, up to 10% may remain viable in excreted feces. Mature berries of these weeds also contain high levels of solanine and solanosine, which are toxic to livestock. Animals should be removed from infested areas until control is achieved.
Experiments have shown that shading reduces silverleaf nightshade berry production and total nonstructural carbohydrate content of the roots. However, there has been little research examining which native California species would compete well with these nightshades.

Chemical: There are few herbicides that effectively control these nightshades, and their application is dependent upon the land use. Herbicide labels should be read and followed in regards to crop rotations and restrictions following application. Herbicides should be applied late bud to early flower. Glyphosate in a 2% solution can be applied as a spot treatment. Dicamba and 2,4-D can be applied at 0.5-1.0 and 1.0-2.0 lb ae/A, respectively. Triclopyr can be applied at 1-3 lb ae/A. Regrowth will occur with any of these treatments and retreatment will be necessary. Picloram has provided excellent control of many of these species in other states, but is not currently labeled in California. Clopyralid has not provided good control of horsenettle or silverleaf nightshade in other states and is not recommended. Glyphosate is non-selective and will injure or kill any foliage it contacts. Dicamba, 2,4-D, and triclopyr will injure or kill most other broadleaf plants. These factors should be considered when applying these herbicides.

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