Solanum americanum Mill.

Mayotte: Solanum americanum flowers and fruits all year round.
New Caledonia: The seeds of Solanum americanum germinate at the beginning of the rainy season and the plant develops very rapidly to realize its flowering in the rainy season, followed by fruiting in the cool season.

In Reunion island there are several forms of Solanum americanum, a smooth and winged stem one and another with a cylindrical and pubescent stem shape, a glaucous-colored form and a green-colored form. More precise observations of these different forms would be necessary to check if all of them correspond to the criteria of S. americanum.

Elements of distinction between Solanum americanum and Solanum nigrum L.
 

From a genome perspective, S. americanum is diploid (24 chromosomes) while S. nigrum is hexaploid (72 chromosomes); actually population genetic analyzes. suggest that S. americanum is the diploid parent of S. nigrum, a species which is the product of an alloautopolyploidization of S. americanum and S. villosum. Solanum villosum is a tetraploid species (48 chromosomes) which is said to be the result of autopolyploidisation of S. americanum. S. nigrum is a form of S. americanum which is very modified in terms of genome size - hence the absence of difference in terms of sterile parts - but the presence of difference (especially in size) concerning the fertile parts (flowers, fruits, seeds and pollen) which is often observed when there is such a radical change in the genome. Finally the most distinctive character is the size of the anthers (information according to Xavier Aubriot).

Table of distintive characters of some Solanum species
 

Comoros: Solanum americanum is present on the three islands up to 1200 m in humid and shady area. It occurs in very fertile soils.
French Guiana: Frequent species in ruderal vegetation and along the canals of the Mana rice polder and crop weed.
Madagascar: current spontaneous species in wetlands (eastern slope) in the plots after recently cleared forest (yet soils rich in organic matter).
Mauritius: Common species throughout the island and especially frequent near houses, It is a very important weed, growing in all conditions.
Mayotte: Solanum americanum is an exotic species sometimes cultivated for its leaves and fruits that are edible after cooking. It is also naturalized and very common in crops, pastures, villages, especially in hygrophilic and mesophilic regions.
New Caledonia: This ruderal and ubiquitous species is widely distributed throughout the country, especially in disturbed or cultivated areas. Adapted to fertile soils, it likes wet soils or dry irrigated areas and is found up to 1000 m altitude.
Reunion: The species is very common in Reunion, in all cool, shady places. It is found throughout moderately humid areas of Northeast coastline, irrigated dry areas, at an average altitude up to 1000 m. It is well suited to very fertile soils, especially rich in nitrogen and phosphorus
Seychelles: common weed of cultivated land from 0 to about 400 m altitude, especially on fertile soils in full sun, but also shaded.
West Indies: Solanum americanum is an indigenous species. It grows in both abandoned and cultivated areas. It has a relatively strong preference for humid and shady areas. It becomes abundant on regularly fertilised plots.
 

Toxicity:

Like many Solanaceae, the foliage and fruits of Solanum americanum are toxic. This toxicity disappear after cooking. It may also have high concentrations of nitrogen.

Global harmfulness

A part from its competitiveness effect on crop Solanum americanum is also a poisonous plant, through its toxicity appears to be variable. In Zimbabwe, for example, the leaves are reported to be eaten as a vegetable and the ripe fruit are also edible. On the hand unripe fruits are poisonous, sometimes only slightly, at other times very much so, especially to children, and cattle have also been affected by grazing on the foliage.

Local harmfulness

Benin: Solanum americanum is rare and scarce in paddy fields.
Comoros: Common weed of cassava crops and also very common in vegetable crops.
Cote d'Ivoire: Frequent and scarce in paddy fields.
French Guiana: Weed not very frequent and rarely abundant in vegetable crops.
Kenya: Rare and scarce in paddy fields.
Madagascar: Due to its vegetative development, it can be detrimental to rainfed rice (tavy rice).
Mali: Rare and scarce in paddy fields.
Mauritius: Weed very harmful in all the local cultures where it develops in abundance.
Mayotte: Solanum americanum is an infrequent weed, present in 5% of cultivated plots, mainly in vegetable crops.
Nigeria: Rare and scarce in paddy fields.
New Caledonia: It has been reported in New Caledonia since the mid-19th century and is now widespread throughout the country, particularly in disturbed and cultivated areas. This ruderal and ubiquitous species may prove to be a weed of the crops that is exhausting for other species because of its important development and nitrophilicity. It is favored by tillage and can be a problem for the establishment of forage species.
Uganda: Frequent and generally scarce in paddy fields.
Reunion Island: Solanum americanum is a weed that is harmful for its rapid development and nitrophilicity. It is common in fields of young sugarcane and vegetable crops.
Senegal: Rare and acarce in paddy fields.
Seychelles: Serious occasional weed of agricultural and horticultural crops such as orchards and vegetable crops. It is a serious competitor for light, water and nutrients from many crops, especially seedling stage.
Tanzania: Rare and scarce in paddy fields.
West Indies: Solanum americanum is a weed species present in all crops. It is not very harmful for sugarcane, banana and fruit crops. However, it is a major pest of vegetable crops when it becomes abundant.

Solanum americanum is a host plant for root-knot nematodes Meloidogyne spp.

Global control

Solanum americanum is moderately supsceptible to 2,4-D and MCPA but the plants are only satisfactorily killed as small seedlings. Mixtures containing bromoxynil, ionynil or dicamba are more effective. Contact herbicides are including bentazon give good control and various residual herbicides are effective as pre-or early post-emergence treatments, including atrazine, diuron, linuron, alachlor and pendimethalin. Metribuzin, however, is not effective against Solanum species.

Management recommandations for perenial broad leaved plants in rice fields: http://portal.wiktrop.org/document/show/20

Local control

New Caledonia: In case of a marked infestation on a pasture by an adult population of Solanum americanum, the association of the mechanical and chemical control easily comes to an end. Growth before flowering should be followed by a spray herbicide treatment on volunteers with sufficient leaves (2 to 3 weeks). A 2,4-D herbicide should be used (see table for products and doses).
Reunion :

Spectrum of effectiveness of herbicides on Solanum americanum in sugarcane cultivation

(doses are expressed in commercial product) - 2014

Data collected in Reunion Island on efficacy of herbicides products under the eRcane Cane Herbicide Network with funding from ODEADOM and ONEMA.
Action led by the French ministry in charge of agri-food and forestry agriculture, with the financial support of the National Office for Water and Aquatic Environments, on credits from the charge for diffuse pollution allocated to the financing of the Ecophyto
West Indies: In order to limit the harmfulness of Solanum americanum, chemical weeding must be complemented by manual and mechanical techniques before the end of the crop cycle.

Herbarium pictures ReCOLNAT: https://explore.recolnat.org/search/botanique/simplequery=Solanum%2520americanum