Weeds

Solanum carolinense L. - Horse-nettle.

Taxonomic position.

Family Solanaceae Juss., genus Solanum L.

Synonyms.

Solanum hirsutum Nitt., S.sodomeum L.

Biological group.

Perennial weed forming rootstocks.

Morphology and biology.

Plant is 30-120 cm in height. Stem is thick, straight, branched, covered with a large amount of stellate hairs and firm yellow thorns that are up to 5 mm in length. Roots are thick, vertical-horizontal. Produces above-ground shoots; horizontal roots diverge from thick vertical root branched in its upper part at depths of 10-30 cm. Vertical roots penetrate down to depths of more than 3 m. Leaves are entire, alternate, with short petioles, pinnatilobate; they are covered with stellate hairs along edges, middle ribs and petioles. Flowers are large, located in upper axillary inflorescences, bisexual, actinomorphic. Calyx consists of 5 lobes. Corolla consists of 5 oval petals having bluish-white to lilac colour. This plant flowers in May-September, bears fruits in July-November. Fruit is a succulent berry, yellow or orange, round, glabrous, containing 40 to 170 seeds. Seeds are yellow or brown, flat, rounded-oval, flattened laterally; their surface is oily and covered with small knobs. S. carolinense reproduces both by seeds and vegetatively. One plant can produce more than 5,000 seeds. Fresh seeds do not germinate, staying dormant for 5-6 months. Optimum temperature for seed germination is 23-25°C; germination also occurs by alternating temperatures from 20 to 30°C. Optimum depth for seed germination is 2-5 cm. Seeds remain viable in soil for more than 3 years. Vegetative reproduction of S.carolinense occurs by rootstocks and root fragments. Parental horizontal roots can reach 1 m before they produce new above-ground shoots, which produce their own vertical and horizontal roots. Thus patches of S.carolinense are formed, having a density of 20 and more shoots per 1 square meter. This plant successfully reproduces from root fragments at soil depths of 30 cm and more.

Distribution.

S.carolinense is an adventive plant; its homeland is the southwest USA. Within the Former USSR it occurs in Abkhazia, Adzharia, Mingrelian and Gurian regions of Western Georgia; sporadically distributed in the Far East, Ukraine, Moldova. Distributed also in North America, India, Japan, Australia.

Ecology.

S.carolinense grows in all types of soils but prefers loose sandy or gravelly soils. This plant is extremely drought-resistant, heat-loving and light-requiring. Its roots are characterized by low frost-resistance; therefore, the potential area of S.carolinense distribution stops at latitude 50°N

Economic significance.

S.carolinense is an extremely competitive weed. It infests corn and other grain crops; potato, soybean, tomato crops; fields of alfalfa and other perennial grasses, gardens, tea-gardens; as a ruderal plant it occurs in pastures and waste places. Plants of S.carolinense contain highly toxic glycoalkaloid solanine; they are poisonous for farm animals and people. S.carolinense is an alternate host for some pests and pathogens of crop plants (Septoria lycopersici, Tobacco Mosaic Virus). Control measures include quarantine phytosanitary measures (prevention of seed spread into new regions, systematic survey of lands, and eradication of initial and isolated foci of S.carolinense); measures of chemical control (herbicide use). Agronomic measures of control are not effective; but when the use of herbicides is impossible, hand weeding by soil digging and thorough removal of roots are recommended on small spots infested by S.carolinense; when sites of infestation are discovered in cultivated lands, the latter should be excluded from crop rotation and converted into clean fallows.

Reference citations.

Basset, I.J. & Munro, D.B. 1986. The biology of Canadian weeds. 78. Solanum carolinense L. and Solanum rostratum Dunal. Canadian Journal of Plant Sciences. 66(10): 977-91.
Moskalenko, G.P. 2001. Quarantine weeds of Russia. Moscow: Rosgoskarantin. 280 pp. (in Russian).
Nikitin, V.V. 1983. Weed plants of USSR flora. Leningrad: Nauka. 454 p. (in Russian).
Ulyanova, T.N. 1998. Weed plants in flora of Russia and other CIS countries. St.Petersburg: VIR. 343 p. (in Russian).

© Larina S.Yu.