Solanum elaeagnifolium Cav.

Code

SOLEL

Growth form

Broadleaf

Biological cycle

Vivacious

Habitat

Terrestrial

Algeria: Solanum elaeagnifolium germinates from winter to spring; suckering also takes place in winter-spring; flowering occurs from March to October.
Tunisia: S. elaeagnifolium has an active vegetative growth phase in spring (March-May). It stops its vegetative growth in June-August, investing its resources in flowering and fruiting. Vegetative growth resumes in September-October and decreases in November, when the plant enters its dormant period.

Solanum elaeagnifolium is a rhizomatous vivacious species.

Solanum elaeagnifolium is a vivacious rhizomomatous species. It reproduces both by seed and by active suckering from the rhizomes. Seeds are produced in very large numbers and spread by fruit-eating birds, water and livestock, especially sheep, whose intestinal transit favours germination. Vegetative reproduction takes place through root buds and rhizomes which give rise to new shoots.

Solanum elaeagnifolium is a mainly hydrochorous and zoochorous species (spread by water and animals).  Root or rhizome fragments can be spread by vehicles or agricultural tools. 

Solanum elaeagnifolium cn reach 120 cm high.

Table of distintive characters of some Solanum species
 

Algeria: Solanum elaeagnifolium is an invasive alien species in all annual and perennial crops, as well as in ruderal habitats (along roadsides, pavements, byways, wadis, and irrigation canals, wastelands) in the north of the country. The semi-arid bioclimate zones with temperate to warm winters as well as the subhumid bioclimate zones with warm winters are its preferred zone, whereas the Saharan climate zones are not suitable for it, although it has been able to establish itself in some oases in the northern Sahara. Solanum elaeagnifolium is particularly fond of cool, nitrogen-rich silty and clayey soils in low-lying areas (0 to 400 m), in arid to humid bioclimates (200 to 1200 mm∕an), with warm to cool winters.  All these edaphoclimatic conditions correspond to the synanthropic vegetation regions of Mediterranean Algeria to the Amnio visnagae-Capnophylletum peregrini zones (Chevassut & Abdelkrim, 1993). This association indicates a heavy marly soil with a remarkable level of humidity as well as a post-vernal phenology. Below 200 mm∕an, the species needs supplementation in the form of crop irrigation water (southern oases).

Sensitive to frost, Solanum elaeagnifolium requires high temperatures (between 20 and 34°C) and significant rainfall to germinate and grow. Once its root system is well established, the plant can withstand drought and develops particularly well in semi-arid conditions (300 to 500 mm of average annual rainfall). However, it adapts readily to a variety of wetter climates and soil types and is relatively tolerant of saline conditions. However, it seems to prefer sandy soils poor in organic matter and open, disturbed, sunny environments. Outside of disturbed areas (including cultivated areas and pastures), it is also invasive along roadsides and waterways.

South Africa: Solanum elaeagnifolium grows in the deciduous Acacia wooded grasslands of the Kalahari. Weed of crops, disturbed land, roadsides, canals.

Sexual reproduction of Solanum elaeagnifolium allows the colonisation of more remote open habitats and the connection of the most isolated population patches. Vegetative regeneration takes place by suckering of the reserve-rich rhizomes, and takes place a little later, when the soil warms up sufficiently from late March to early April (in Algeria). The suckers have the advantage of occupying the soil more quickly and efficiently (high local density of modules or ramets physiologically connected by hypogeotropic rhizomes) than do the seedlings, and as they grow older they bear long spines at the base, which discourage any attempt to remove them. By forming an uninterrupted front of aggregated modules, which spread slowly and thus exclude other plants from their territory (consolidation strategy), this clonal species presents a phalanx growth strategy (densely arranged in the manner of the Roman phalanxes), according to Lovett-Doust (1981), which is efficient in terms of space capture. However, it should be noted that the prevalence of the vegetative propagation mode does not promote an increase in genetic diversity, even if seed germination has sometimes been observed. At the same time, a very high rate of self-pollination has been observed in vegetatively propagated species, leading to genetic monotony and making them less able to respond to environmental changes. As a result, a conflict situation coexists between sexual and asexual reproduction, a trade-off between colonisation and spatial consolidation. A situation very similar to that of other vivacious weeds such as Oxalis pes-caprae L.

Toxicity

Solanum elaeagnifolium is known to be toxic to livestock, causing damage to the intestinal tract and nervous system and, in severe cases, can cause hallucinations, paralysis and death.

Local harmfulness

Algeria: Solanum elaeagnifolium is a major and invasive "weed". It is one of the most harmful species of field crops because it can colonise practically all ecological environments (very frequent species), moreover its great adaptation to the agricultural environment gives it a very important potential of invading plots (very abundant species). Due to its spring germination extending into summer, this taxon is very limited in development in autumn crops (winter cereals and pulses); there, it is more successful in sparse crops (broadcast winter cereals) or in rows (chickpeas sown in rows and harvested late in summer, in particular). It is particularly infesting in irrigated summer annual crops (maize, vegetable crops) as well as in palm groves. Orchards, especially citrus and olive groves, are particularly infested because of the multiple superficial mechanical interventions they require (cutting and spreading of rhizomes).

Global harmfulness

Solanum elaeagnifolium is considered a tenacious weed in many arid to semi-arid regions, including India, Australia, South Africa, the Pacific Islands and the USA. It is invasive in Cuba and Hawaii, and considered a major weed in India and Java. It has been declared a noxious weed in the US states of Arkansas, California, Idaho, Nevada and Washington, and designated as an 'A' weed for quarantine in Oregon and Washington. The species competes with crops, interferes with livestock, hosts insects and plant diseases...

In some crops and pastures, under semi-arid and irrigated conditions, Solanum elaeagnifolium behaves like a plant pest as it competes strongly for soil water resources and nutrient availability (due to its extensive and deep root system). Eventually, it can form dense, monospecific plant mats, causing severe yield losses. The young fruits and leaves are also known to be toxic to livestock (cows, sheep, horses). Cows seem to be more sensitive than sheep; goats do not show symptoms of poisoning. However, in South Africa, during severe drought conditions, the plant is consumed by cattle and some wild herbivores which do not seem to be affected.

Local harmfulness

South Africa: Solanum elaeagnifolium is an invasive alien species present throughout the country. It forms dense and extensive infestations that compete with cultivated plants. It is extremely difficult to eradicate because it has deep, extensive roots and the ability to regenerate from small root fragments. The plants are poisonous and unpalatable.

In California, Solanum elaeagnifolium is known as a vector of Lettuce chlorosis virus. It is also recorded as a secondary host of several insect pests such as the Colorado beetle (Leptinotarsa decemlineata) in Texas and the pepper weevil (Anthonomus eugenii Cano) in Florida.

Global control

Biological control: Several countries, including South Africa and Australia, have studied the feasibility of biological control of Solanum elaeagnifolium, but only South Africa has imported, tested and released agents so far. Two leaf-eating beetles, Leptinotarsa texana and Leptinotarsa defecta (Chysomelidae) have become established in South Africa following deliberate releases. The phytophagous nematode Ditylenchus phyllobius (= Orrina phyllobia) has established in India and was probably originally introduced with the plant. Consideration was given to releasing D. phyllobius in South Africa, but this was rejected because of doubts about its host specificity.

Local control

Algeria: Long-term integrated control methods of Solanum elaeagnifolium should combine :

  -  Mechanical control through deep to medium ploughing repeated several times a year (especially in summer) and for several years immediately followed by a collection/incineration or burial operation;
  -  Although difficult to achieve in the current environmental context, chemical control through the use of certain herbicides such as those based on glyphosate or trichlopyr is an option that can be considered to contain particularly dense stands on roadsides. However, this is not a sustainable solution;
  -  Cultural control by opting for alfalfa for its allelopathic effect;
  -  Solarisation as a hydrothermal technique for destocking infested soils, as well as careful and compulsory composting of manure;
 -   A ban on moving soil (such as during road development or tidal flats) that may contain pieces of rhizomes ensuring dispersal
  -  A ban on grazing in infested areas;

Now that the eradication measures for Solanum elaeagnifolium have been taken, a well-reasoned national control strategy remains to be put into practice.