Nightshades
Black nightshade, Solanum nigrum L.
Eastern black nightshade, Solanum ptycanthum Dunal
Hairy nightshade, Solanum physalifolium Rusby = S. sarachoides auct. non Sendtn.



Images above: Upper left: Black nightshade seedlings (Jack Clark, University of California). Upper right: Black nightshade ripe fruit (Antonio DiTommaso, Cornell University). Bottom: Black nightshade plant (Jack Clark, University of California).



Images above: Upper left: Eastern black nightshade underside of leaves (Randall Prostak, University of Massachusetts). Upper right: Eastern black nightshade flowers (Randall Prostak, University of Massachusetts). Bottom: Eastern black nightshade young plant (Antonio DiTommaso, Cornell University)



Images above: Upper left: Hairy nightshade seedling (Jack Clark, University of California). Upper right: Hairy nightshade ripe fruits (Joseph DiTomaso, University of California, Davis). Bottom: Hairy nightshade plant (Joseph DiTomaso, University of California, Davis).
Identification
Other common names:
- Black nightshade: deadly nightshade, poison berry, garden nightshade, hound's-berry, garden huckleberry
- Eastern black nightshade: deadly nightshade, poison berry, garden nightshade, West Indian nightshade
- Hairy nightshade: no other common names located.
Family: nightshade family, Solanaceae
Habit: Erect, branched, summer annual herbs.
Description: Seedlings have egg to lance shaped cotyledons. The stem of the seedling is hairy. Young leaves are alternate.
- Black nightshade: Cotyledons are 0.1-0.4” (0.25-1 cm) long by 0.1” (0.25 cm) wide and pointy tipped with small, sticky hairs on the leaf edges, below the midvein, and scattered on the leaf surface. The first leaf is spade shaped, subsequent leaves are oval or egg shaped. Young, light green leaves are wavy, and hairy on all surfaces and edges, with prominently veined, purple tinged undersides.
- Eastern black nightshade: Cotyledons are 0.4-0.5” (1-1.2 cm) long by 0.1-0.2” (0.3-0.5 cm) wide on 0.1-0.2” (0.3-0.5 cm) long stalks and have green upper surfaces and green to maroon, prominently veined undersides. The stem of the seedling is green with a red hue. Stems and stalks above the cotyledons are purplish, with absent or inconspicuous hairs. Young leaves are egg shaped and nearly hairless, with wavy edges and purple-tinged undersides.
- Hairy nightshade: Cotyledons are egg to lance shaped, 0.17-0.4” (0.4-1 cm) long, and green on both surfaces, with hairs on leaf edges and stalks. Young leaves are oval to elliptical, wavy edged, and hairy.
Mature plants have round, ridged, woody, green stems. Leaves are stalked and alternate on the stem. When present, toothing is coarse, irregularly spaced, and rounded. Fibrous roots branch from the shallow taproot.
- Black nightshade: Branching begins low on the stem and stems can reach 1.75-3 ft (0.5-0.9 m) tall. Dark green leaves are 1-5” (2.5-13 cm) long by 0.5-2.5” (1.3-6.4 cm) wide and oval to egg shaped, with tapering to the tip and wavy edges. Edges have purple undersides. Toothing is present on lower leaves and absent on upper leaves. Sparse, non-sticky hairs are typically present on stems, leaf undersides and leaf stalks.
- Eastern black nightshade: Stems are hairless to lightly hairy and can reach 1-3.3 ft (0.3-1 m). Leaves are 1-3” (2.5-7.5 cm) long by 0.4-2.25” (1-5.7 cm) wide and elliptical to triangular-egg shaped. Leaves are nearly hairless. Edges are toothed, wavy, and red-purple underneath.
- Hairy nightshade: Stems are slender, often coated in sticky, spreading hairs, and typically reach 1-2 ft (0.3-0.6 m) but sometimes 3 ft (0.9 m) in height. Leaves are egg to lance shaped, 0.75-3” (1.9-7.5 cm) long by 0.25-2.25” (0.6-5.7 cm) wide, with fine, spreading hairs on the undersides of large veins and sometimes on leaf surfaces. Leaf margins are lightly toothed or untoothed.
Flowers are star-shaped individually stalked, and made up of 5 fused petals and a cone of yellow anthers; flowers are clustered and have 5 small, green sepals at the flower base.
- Black nightshade: Each cluster has 5 to 10, white to pale blue, drooping, 0.25-0.4” (0.6-1 cm) wide flowers. The stalked flowers arise from an unbranched central axis.
- Eastern black nightshade: Each cluster has 4 to 7 drooping, white to light purple, 0.25-0.4” (0.6-1 cm) flowers. Flower stalks arise from a common point.
- Hairy nightshade: Each cluster has 4 to 5, white, 0.3-0.5” (0.8-1.3 cm) wide flowers. The flower stalks generally arise from an unbranched central axis but occasionally can arise from a common point.
Fruit and Seeds: Berries are green when immature. Seeds are flat. Only hairy nightshade berries are partially enclosed by sepals.
- Black nightshade: Dull, blue-black berries are 0.4-0.6” (1-1.5 cm) wide and each contains 15 to 60 yellow to light brown (sometimes white), pointed, oval, 0.06” (0.15 cm) long seeds. Berries fall off the plant before the first frost.
- Eastern black nightshade: Shiny, purple-black berries are 0.4” (1 cm) wide and each contains 50 to 110 round, yellow to white, dull, 0.06-0.08” (0.15-0.2 cm) long seeds. Berries are retained after the first frost.
- Hairy nightshade: Yellow green to olive or slightly purple-green berries are 0.2-0.4” (0.5-1 cm) wide and each contains 10 to 36, round or oval, 0.07-0.09” (0.18-0.23 cm) diameter, tan seeds.
Similar species: Silverleaf nightshade (Solanum elaeagnifolium Cav.) has large, showy purplish flowers, thorny stems, gray-green leaves, rhizomes, and a perennial habit. American black nightshade (Solanum americanum Mill.) has wide cotyledons, hairless stems, and leaves that have no or only shallow toothing; its habit is upright, but its branches are closely clumped, not spreading. Leaves and flowers of horsenettle (Solanum carolinense L.) are similar, but it is a perennial with large, sharp spines on stems and leaves, and spreads by underground storage roots. Bittersweet nightshade (Solanum dulcamara L.) is a larger, vining perennial with red berries.
Management
Black nightshades not only compete with crops and reduce crop yields, but they also interfere with harvest and lower crop quality. The berries stain and cause soil to stick to beans, thereby causing much crop loss (Ogg and Rogers 1989, Werner et al. 1998). They are impossible to separate from peas, leading to downgrading of the crop. The berries also add moisture to a range of combine harvested crops, leading to growth of molds (DeFelice 2003, Ogg and Rogers 1989). Normal tillage and cultivation practices are usually sufficient to keep light infestations under control. When growing dry beans, food grade soybeans, or peas, however, eradicate any newly established populations and attack established populations with all measures available. Avoid excessive N as this will favor these weeds relative to most crops (Gonzalez Ponce and Salas 1999). Use good cropping practices, relatively high seeding rates and narrow row spacing to get dense, uniform stands that will suppress nightshade (Rich and Renner 2007, Stoller and Myers 1989, Werner et al. 1998). Soil disturbance promotes nightshade emergence and, when practical, no-till systems can reduce nightshade densities (Peachy et al. 2004).
These species form moderately persistent seedbanks but they germinate throughout spring and summer in response to tillage. Consequently, the seeds are relatively easy to flush out of the soil with cultivated fallow periods interspersed into the crop rotation, or with short cycle vegetable crops in which the weeds do not have time to produce mature fruits. Sod crops set back populations of these weeds since they do not tolerate repeated mowing or competition from the perennial forages. In pastures these nightshades can be controlled by avoiding overgrazing. Intensive rotational grazing is especially effective since the repeated grazing episodes will destroy successive flushes of seedlings.
These weeds harbor many diseases, insect and nematode pests of solanaceous crops like potato, tomato and pepper (DeFelice 2003, Boydston et al. 2008). If they are allowed to grow during break periods between these crops, they will negate many of the benefits of crop rotation for disease and pest control. Consequently, escapes should be hand rogued out of break crops and removed from the field.
Solarization to temperatures of 122-131 °F (50-55 °C) for at least two days completely inhibits germination of these species from the upper soil layer (Givelberg et al. 1984).
Ecology
Origin and distribution: Black nightshade was apparently introduced from Europe (DeFelice 2003, Edmonds and Chweya 1997). It occurs on the east and west coasts, but is primarily a problem on the west coast (USDA Plants). It also occurs in Asia, Africa, Australia and South and Central America. Eastern black nightshade is native to eastern North America and is the most common member of the black nightshade group east of the Rocky Mountains (DeFelice 2003). Hairy nightshade is a native of southern South America that has been introduced into North America, Europe, Africa, Australia, and New Zealand (Edmonds and Chweya 1997). In North America it occurs throughout most of southern Canada and the U.S.A. except the deep South (USDA Plants). It is most common, however, in the prairie region and the Pacific Northwest.
Seed weight: Black nightshade - 0.70 mg (Gaba et al. 2019), 0.80 mg (Benvenuti et al. 2001), 1.3 mg (Fortuin & Omta 1980); eastern black nightshade - 0.43 mg (Mohler, unpublished data).
Dormancy and germination: The percentage of fresh black nightshade seeds that are dormant varies with the population (Taab and Andersson 2009c), and some populations have little or no dormancy once they are separated from the berry (Bassett and Munro 1985, Givelberg et al. 1984). As little as one week of wet storage at 40-59°F (5-15°C) is sufficient to break dormancy (Taab and Andersson 2009b). Black nightshade seeds germinate best with fluctuating temperatures with an amplitude range of 9-27°F (5-15°C) and including a high temperature of 77-86° F (25-30° C ) (DeFelice 2003, Roberts and Lockett 1978, Taab and Andersson 2009b). Constant temperatures may result in poor germination (Roberts and Lockett 1978). However, some studies have found good germination at constant temperatures of 59-86°F (15-30°C)(Givelberg et al. 1984, Ma et al. 2021) provided seeds received a pretreatment with wet, cool conditions to reduce dormancy (Taab and Andersson 2009b). Hot summer temperatures (e.g., 93-100°F (34-38°C) induce secondary dormancy (Taab and Andersson 2009a, 2009b). Nitrate and light promote germination of black nightshade (Roberts and Lockett 1978). Light is a requirement for germination at constant temperature, but is less important at alternating temperatures (Givelberg et al. 1984).
Eastern black nightshade germinates best in light at temperatures from 77-86 °F (25-30 °C) or with alternating temperatures including a high temperature of 86 °F (30 °C) (Bassett and Munro 1985, Thomson and Witt 1987, Weaver et al. 1988, Zhou et al. 2005). Several days exposure to full sunlight, however, completely inhibits germination. Nitrate increases germination of seeds that have been exposed to light. The base temperature for emergence is 52-55 °F (11-13 °C) (Weaver et al. 1988). Eastern black nightshade requires several more days to emerge than other weeds and tomato (Weaver et al. 1988). Germination is optimum at pH 5 to 8 (Thomson and Witt 1987)
Hairy nightshade seeds are usually dormant initially (Roberts and Boddrell 1983, Taab and Andersson 2009c) but lose dormancy after 1 to 6 months, under a wide range of conditions (Basset and Munro 1985, Peachey and Mallory-Smith 2007, Roberts and Boddrell 1983). Seeds germinate well at 77-92 °F (25-33 °C), but poorly at 50-73 °F (10-23 °C) and at 97 °F (36 °C) (Bassett and Munro 1985, Peachey and Mallory-Smith 2007, Roberts and Boddrell 1983). Fluctuating temperatures increase germination of seeds that have not fully after-ripened by lowering the base temperature from 70 °F (21 °C) to 54 °F (12.5 °C) (del Monte and Tarquis 1997). Seeds of black and hairy nightshade enter a secondary dormancy in late summer/early fall (Roberts and Boddrell 1983).
Given their seed germination characteristics, stimulation of emergence of these nightshade species by tillage is not surprising (DeFelice 2003, Ogg and Dawson 1984, Peachey and Mallory-Smith 2007).
Seed longevity: Black nightshade seeds can survive up to 39 years in undisturbed soil (Toole and Brown 1946). Experiments in annually tilled soil, however, showed numbers of black nightshade seeds declined by 37% per year (Popay et al. 1994). Under similar tilled conditions, average seed losses over a five-year period were 28-45% per year (Roberts and Lockett 1978). Hairy nightshade appears to be less persistent than black, but at least a few seeds last up to 5 years in the soil (Roberts 1986). All hairy nightshade seeds survived one year in experiments at two locations in Nebraska, but survival dropped to 11% and lower after two and subsequent years at one location, whereas it remained at 65% after 17 years at the other location (Burnside et al. 1996).
Season of emergence: The black nightshades begin emerging in mid-spring and continue through summer whenever moisture is adequate (DeFelice 2003, Doll 2002, Ogg and Dawson 1984, Roberts and Lockett 1978, Roberts and Boddrell 1983, Uva et al. 1997). Eastern black nightshade was classified as a late-emerging species in comparison to seven other common weeds in the mid-Atlantic states (Myers et al. 2004), but was classified as a middle-emerging weed with a longer emergence period than most other species in Nebraska (Werle et al. 2014). Emergence of nightshades tends to peak in spring when air temperature reaches 68 °F (20 °C) (Ogg and Dawson 1984) or when mean soil temperatures reaches approximately 59 °F (15 °C) with an amplitude range of 18 °F (10 °C) (Taab and Andersson 2009c).
Emergence depth: Black nightshade emerges well from seeds within the top 1.6” (4 cm) of soil. A few seedlings can emerge from seeds at 2.4-3.1” (6-8 cm) but none from seeds at 4” (10 cm) (Benvenuti et al. 2001, Ogg and Rogers 1989). Eastern black nightshade emerged better from the soil surface than from 0.6” (1.5 cm) depth, probably due to its smaller seed (Weaver et al. 1988).
Photosynthetic pathway: C3
Sensitivity to frost: Black nightshade plants are sensitive to even light frost, but hairy and eastern black nightshades are more tolerant of light frost (Edmonds & Chweya 1997, Ogg and Rogers 1989, Roberts and Lockett 1978). The seeds of black and eastern black nightshades do not tolerate cold temperatures such as during winter on the Canadian prairies, but hairy nightshade seeds can tolerate such conditions (Bassett and Munro 1985).
Drought tolerance: All three species require moist soil for good growth. They wilt quickly when water stressed but may recover again if the drought period is short. Black and eastern black nightshades are generally absent from regions with dry climates except in irrigated fields (Holm et al. 1977), but hairy nightshade tolerates drier conditions (Edmonds and Chweya 1997).
Mycorrhiza: Black nightshade is mycorrhizal (Harley and Harley 1987, Vatovec et al. 2005).
Response to fertility: These species are highly responsive to N and P fertility and will store excess N as nitrate (Bassett and Munro 1985). For example, black nightshade accumulated more than twice as much nitrate at the flowering stage as tomato and pepper (Gonzalez Ponce and Salas 1999) and uptake of major nutrients by these crops was reduced when competing with eastern black nightshade (Gonzalez Ponce et al. 1996). Hairy nightshade plants increased in size up to nitrogen application rates of 430 lb/acre (480 kg /ha) with a relative response that was similar to wheat (Blackshaw et al. 2003). This species showed the strongest response to increasing P levels of 22 weeds and two crops tested (Blackshaw et al. 2004). The black nightshades grow best at a pH of 6.0-6.5 (Edmonds & Chweya 1997).
Soil physical requirements: These species will grow on a wide range of soil textures from sandy loam to clay, but do best on fertile soils with good moisture holding capacity (DeFelice 2003, Uva et al. 1997). They do not tolerate poor drainage.
Response to shade: Eastern black nightshade tolerates only light shade. Shade levels of 60, 80 and 94% relative to full sunlight reduced growth by 48, 83 and 98% and berry production by similar amounts (Stoller and Myers 1989). Plants within soybean rows were only one third as large as plants between the rows. However even the smallest plants subjected to the most shade produced some seeds to replenish the seedbank (Stoller and Myers 1989). Black nightshade is more shade tolerant than eastern black. For example, moderate shade of 50-60% had little effect on plant biomass and increased leaf area of black nightshade, but greater than 75 % shade reduced all measures of plant size (Fortuin & Omta 1980). In hot dry conditions, partial shade appears to promote growth and survival of black nightshade (Edmonds & Chweya 1997).
Sensitivity to disturbance: Plants re-sprout vigorously following severe and repeated cutting (Edmonds & Chweya 1997).
Time from emergence to reproduction: Black nightshade plants emerging in spring require 7-9 weeks before flowering (DeFelice 2003, Roberts and Lockett 1978). In midsummer, flowers begin opening 5-6 weeks after emergence (Ogg and Rogers 1989). Eastern black nightshade flowered 5-10 weeks after emergence (Doll 2002, Quakenbush and Anderson 1984). Nightshade berries mature 4-5 weeks after pollination (Quakenbush and Anderson 1984, Roberts and Lockett 1978) although maximum seed viability of eastern black nightshade was not reached until 6 to 8 weeks after flowering (Thomson and Witt 1987). Fruit production in all species continues until frost.
Pollination: All three species commonly self-pollinate but also are cross pollinated by insects (DeFelice 2003, Edmonds & Chweya 1997).
Reproduction: Eastern black nightshade plants growing outside in Ontario produced 50-100 berries, and at least 2,500-5,000 seeds each (Bassett and Munro 1985). In Minnesota, eastern black nightshade without competition produced 2,700-7,400 berries containing 252,000-825,000 seeds per plant. However, maximum seed production with soybean competition was 2,500 seeds per plant (Quakenbush and Anderson 1984). In Illinois, individual plants produced 6,000 berries with 500,000 seeds under the most favorable conditions (Stoller and Myers 1989). In California, black nightshade averaged 60 seeds per berry and 60,000 seeds per plant (DeFelice 2003), whereas hairy nightshade averaged 20 seeds per berry and 16,000 seeds per plant (Kempen and Graf 1981). Black nightshade berries fall off the plant when mature (Edmonds and Chweya 1979), but eastern black nightshade plants remain upright with some berries intact on the plant after frost has killed the plants (Uva et al. 1997).
Dispersal: Seeds of all three species are spread by birds, rodents and livestock that eat the berries (Tamboia et al. 1996). The seeds pass unharmed through the bird and mammal digestive tracts (Barnea et al. 1990, DeFelice 2003, Roberts and Lockett 1978). The berries also disperse by water (DeFelice 2003) as well as hay, straw, or crop seed (Werner et al. 1998). (Edmonds and Chweya 1997)
Common natural enemies: The nightshades are attacked by Colorado potato beetle (Leptinotarsa decemlineata) (Ogg and Rogers 1989), tobacco and potato flea beetles (Epitrix hirtipennis and E. cucumeris) and spinach leaf miner (Pegomya hyoscyami) (Metcalf & Flint 1951). They also host bean aphid (Aphis fabae) which can cause leaf curling and death of nightshade shoot tips (Edmonds & Chweya 1997). Like domesticated species in the nightshade family, these weedy nightshades are attacked by many fungal and viral diseases (Farr et al. 1989, Zitter 2001).
Palatability: Berries and foliage can be poisonous to humans and livestock, and immature berries are particularly toxic (Burrows and Tyrl 2006, Ogg and Rogers 1989). Nightshade plants mixed with forage remains poisonous and can cause intestinal dysfunction and many other symptoms in livestock (Werner et al. 1998). Toxicity is associated with alkaloids and high accumulations of nitrate (Edmonds & Chweya 1997, Ogg and Rogers 1989, Weller and Phipps 1978/1979). However, concentration of the these toxins apparently varies greatly, and is reduced in boiled leaves and ripe berries (DeFelice 2003, Edmonds & Chweya 1997). The nutritional value of leaves and berries is generally high although it can vary depending on soil fertility, age and species (Fortuin and Omta 1980, Edmonds & Chweya 1997). In the U.S.A., the berries of these weeds are sometimes used to make jam. In Africa, Central America and southeast Asia, people eat the fruit of black nightshade and use the leaves as a cooked vegetable (Edmonds & Chweya 1997). Domesticated varieties of black nightshade are grown for the fruit and leaves in many countries (Fortuin and Omta 1980, Edmonds & Chweya 1997) and are called 'garden huckleberry' in the U.S.A. (DeFelice 2003). Leaves of plants grown in shade were considered more palatable and less bitter than leaves grown in full sun (Fortuin and Omta 1980).
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