Revue Marocaine de Protection des Plantes, 2010, N° 1: 1-9.

Solanum elaeagnifolium Cav.: a threat to agriculture and environment in mediterranean region

Solanum elaeagnifolium Cav: une menace à l’agriculture et à l’environnement dans la région méditerranéenne

BOUHACHE M.

Institut Agronomique et Vétérinaire Hassan II, Rabat, Maroc

ABSTRACT

Native to tropical America (, north-east and south–west USA), Solanum elaeagnifolium Cavanilles (Silverleaf nightshade) is a deep rooted perennial broadleaved trans continents weed. It is propagated by seed and/or vegetative fragments of the all organs. It was reported as a weed or /and a colonizing invader species in many countries in Africa; Europe; Americas; Asia and Oceania. S. elaeagnifolium was introduced to these countries as seeds or vegetative fragments by contaminated seeds, fodder, ballast and bedding used in animal transport. The rapid dissemination of this species may be explained by its high vegetative regeneration capacity, high seed production per plant and diversification and efficacy of spreading means and ways. Since S. elaeagnifolium is officially declared as a noxious weed, a control strategy programme should be established on the basis of prevention and control. The prevention includes legislation or regulatory aspects, avoidance of spread means and extermination of isolated and small patches as they appear. Cultural, mechanical, chemical and biological control methods may be used separately or combined in an integrated way to keep this weed under control.

Key words : Solanum elaeagnifolium , silverleafnightshade, importance, impact, control.

RESUME

Originaire de l’Amérique tropicale (Argentine, Nord- Est du Mexique et Sud-ouest des USA), Solanum elaeagnifolium Cavanilles (Morelle jaune) est une adventice dicotylédone vivace et trans continentale. Elle est disséminée par la semence et/ ou les fragments végétatifs de toute la plante. Elle est reportée comme adventice et/ ou espèce envahissante dans plusieurs pays de l’Afrique, Europe, Amériques, Asie et Océanie. S. elaeagnifolium a été introduite dans ces pays sous forme de semences ou fragments végétatifs contaminant les lots de semences, les fourrages, les cargaisons, la litière lors de transport des animaux. La dissémination rapide de cette espèce peut être expliqué par sa grande capacité de régénération végétative, sa grande production semencière par plante et la diversification et l’efficacité des moyens ou facteurs de sa dissémination, Etant déclarée officiellement comme espèce nuisible, le programme d’une stratégie de lutte doit être établi sur la base de la prévention et le contrôle. La prévention englobe la législation ou aspects réglementaires, moyens de dissémination, éradication des individus isolés ou des petits foyers dès leur apparition. Les méthodes de lutte culturale, chimique et biologique peuvent être utilisées séparément ou combinées selon les principes de gestion intégrée de cette espèce.

Mots clés : Solanum elaeagnifolium , morelle jaune, importance, impact, lutte. 1

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SPECIES IDENTITY , Lesotho, Morocco, , Tunisia and in Africa; in Solanum elaeagnifolium Cavanilles Croatia, Cyprus, France, , , (Silverleaf nightshade) is a summer deep Macedonia, Serbia and Spain in Europe; rooted perennial broadleaved weed Argentina, , Guatemala, Honduras, belonging to family with a Mexico, Puerto Rico and USA (Alabama, predominant chromosomes number of Arizona, Arkansas, California, Colorado, 2n=24. Although it bears eight scientific Florida, Georgia, Hawaii, Idaho, Illinois, names and more than 25 vernacular or Indiana, Kansas, Kentucky, , common names, Solanum elaeagnifolium Maryland, Mississippi, Missouri, Cav. and Silverleafnightshade are Nebraska, Oregon, South Carolina, universally used to identify it (EPPO, Tennessee, Texas, Utah, Washington) in 2007). The species may display some Americas; in , Palestine/, Syria forms or variants that confuse its and Taiwan in Asia and in (all taxonomic status. For example, in states) in Oceania (EPPO, 2007). Morocco, two variants of this species were observed in infested areas, one has BIOLOGICAL AND ECOLOGICAL TRAITS white flowers and the other has violet flowers. Palynological, The rapid dissemination and /or phytodermatological and morphological weediness of this species may be studies showed no differences and explained by its high vegetative conclude that the two variants belong to regeneration capacity, high seed the same taxonomic unit. However, production per plant, diversification and karyological investigations indicated that efficacy of spreading means and ways, white flowers variant was characterized and its adaptation to a wide range of by the presence of B chromosome and a habitats. satellite. The violet flowers variant was characterized by the presence of Vegetative regeneration interchromosomal liaisons phenomenon (Khanas, 1996). S. elaeagnifolium is a perennial geophyte with a long, robust and extensive root ORIGIN AND GEOGRAPHICAL system that grows up to 5m vertically and DISTRIBUTION 2m horizontally. It regenerates from stem, root collar; vertical and lateral It is not certain that S. elaeagnifolium underground roots fragments (Tahri et originates from north or south Americas, al., 1988). However, root system gives but most likely between North east high vegetative regeneration and more Mexico and South west of than 45% of roots are located in top of America (USA) (Heap and Carter, 30cm. Root fragments as small as 0.5cm 1999). From there it spread to many long and as deep as 20 cm deep can places around the world that have similar regenerate. The polarity persists in cut climates to this putative area of origin. fragments with fewer shoots forming on The spread and weediness of the species fragments from horizontal roots than is due to some biological and ecological from vertical ones. Buried in soil, the traits. root fragments may maintain their viability for up to 15 months. In addition, Thus, it was reported as a weed or /and a 5 to 10 days old seedlings get the colonizing invader species in Algeria, perennial status and can regenerate

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vegetativelly once clipped. Furthermore, seed bank, in heavily infested area of a study of S. elaeagnifolium dynamic in Morocco, reached 9253, 13229, 20461 sugarbeet and wheat, grown in heavily and 33672 viable seed/m 2 to a depth of infested region in Morocco, showed that 60 cm , respectively for annual crops, the first emergence of the weed came fallow, orchards and roadsides or field from vegetative regeneration and this edges (Tahri et al., 1989). Although, soil way of reproduction dominated the seed bank of S. elaeagnifolium is huge, infestations of these crops (Ameur and only 22-42 % of fieds infestations came Bouhache, 1984). from seeds.

Seed production Dissemination and spread

Although reproduction by seeds is S. elaeagnifolium has already entered secondary, a plant of S. elaeagnifolium and/or established in different countries produces 50 -200 berries/season with 30- by a variety of efficient means or 180 seeds/. The seeds are flat and pathways of dissemination. Spread can coated with mucilage. Thus, a plant may occur both by seeds or vegetative produce 1500-36000 seeds over a long fragments of any part of the plant. Thus, period and with high levels of viability S. elaeagnifolium diaspora can be and dormancy. This physiological trait dispersed by contaminated seeds, fodder, allows the produced seeds to stay viable ballast and bedding used in animal in soil at least 10 years and explains the transport. However, livestock and low germination and/or emergence of the manure, irrigation water, agricultural species. In addition, some studies machinery, nursery plants and indicate that 10-67, 70 and 58% of S. contaminated straw or seeds are elaeagnifolium seeds may still alive after considered to be the main agricultural passing through the digestive tract of practices spreading the weed inside of a sheep, transporting by irrigation water country or a region, as it has been shown and contaminating organic manure, in Morocco (Bouhache and Ameur, 1999) respectively. The resistance to dispersal (Table 1). adverse, high dormancy and few germination of seeds are clues why soil

Table 1: Main sources of S. elaeagnifolium infestations in Morocco

Source Sample size Number of seeds/sample Viability (%) Organic manure 1kg 37 58 Sheep dung 100 units 26 66 Irrigation water 1trap/8hours 22 70 Machines 1kg 30 52 Crop Seeds (Wheat, 0.2 -0.3 kg 0 0 Cotton, Lucerne)

In addition, dead branches bearing or not first patches could be contained and ripe fruits may be disseminated on the prevented to spread if taken at a very ground by wind over hundreds of meters. early stage. This tactic should be based So, where S. elaeagnifolium is already on a monitoring and/or a scouting of a declared as a noxious species, the weed country and especially of the favourable can not be contained anymore. However, places of its introduction. 3

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Adaptation elaeagnifolium have allelopathic effect on several crops such as cotton, The adaptation of S. elaeagnifolium to a cucumber and on pastures establishment. wide range of habitats is another key It was also reported that S. factor behind its invasiveness or/and elaeagnifolium constitutes a reservoir for weediness around the world. The species Lettuce Chlorosis Virus in California and is thermophile, grows in the warm and Potato Virus Y in Tunisia and plays the temperate regions with an annual rainfall role of secondary host of several insect of 250-600 mm and may be found at an pests (EPPO, 2007). altitude of 1200m. In addition, the weed appears to be adapted to a wide range of In addition, infested lands lose soil textures. Thus, it infests cultivated considerable rental and resale values. For lands, orchards, managed and natural example, in Morocco, the value of grasslands, sides of roads; railways; infested lands (Tadla region) decreased canals and rivers and wastelands. It is by 25%. In extreme cases, infested farms also reported that established plants of S. have been abandoned in the USA (EPPO, elaeagnifolium are highly resistant to 2007). Although little information is drought (owing to their deep root system) available on its environmental impact, S. and tolerate saline conditions. However, elaeagnifolium could threaten natural frost and flooding conditions limit its areas and lands by replacing or displacing growth and development or its the native or/and naturalized vegetation distribution area (Heap and Carter, 1999; and as consequences jeopardize certain EPPO, 2007) touristic activities in certain countries, e.g. games in South Africa. IMPACT CONTROL METHODS Although S. elaeagnifolium may invade pastures and grasslands, the species is When S. elaeagnifolium is officially mainly limited to anthropised habitats. It declared as a noxious weed, a control competes with crops and valuable pasture strategy programme should be species for moisture and nutrients, established on the basis of prevention and releases allelopathic compounds, control. The prevention includes interferes with animal husbandry and legislation or regulatory aspects, harvesting practices and harbours insect avoidance of spread means and pests and pathgens (Boyd et al., 1984). extermination of isolated plants and small Since S. elaeagnifolium is a spring patches as they appear. Cultural, growing weed, its life cycle coincides mechanical, chemical and biological with those of spring crops. However, in methods may be used separately or autumnal crops, the weed is only present combined in an integrated way to keep during the second half of their life cycle this weed under control. (Tanji et al. 1984). Thus, crop production losses up to 64, 12 to 50, 5 to 75, and 4 to Cultural methods 10% were reported in maize in Morocco, wheat in Australia, cotton in USA, and Deep ploughing during summer, frequent sorghum in USA, respectively (Heap and clipping at flower initiation stage, dense Carter, 1999; EPPO, 2007). In addition, pasture and Lucerne are implemented as saponines in the fruits of S. methods to reduce the weed infestation.

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The sweep (V shape knifes) was tested in Zaki (2002) demonstrated that Alfalfa heavily infested region of Morocco to cut might reduce density, biomass and fruits root system at a soil depth of 20-25cm. production of the weed by 67-95%, 80- When used at flowering and fruiting 99% and 100%, respectively. The level of stages of the weed, this deep cultivation control was more infuenced by cutting tool allowed to reduce density by 89 and season. Besides frequent cut and shading, 80%, biomass by 90 and 86%, fruits Alfalfa has potential allelopathic effects production by 100% , respectively (Zaki (Bouhache and Assali, 1995). In et al., 1995). Good control of the species laboratory conditions, aqueous extracts was also achieved when deep soil from shoot and root of alfalfa inhibited ploughing was followed by one seeds germination and growth of S. application of glyphosate (Ameur and elaeagnifolium. Among nine isolated Bouhache, 1997; Ameur el al;, 2007). phenolic acids, ferrulic, P.coumaric, Alfalfa ( Medicago sativa ) grown for hay salicylic and gentisic showed high may be included in crops rotation to herbicidal effect (Table 2) (Bensellam, effectively suppress S. elaeagnifolium . 2003). Based on a three years trial, El Jadd and

Table 2: Effect of aqueous extracts of Alfalfa on germination and regeneration of S.elaeagnifolium

Compounds Presence Inhibition (%)

Roots Shoots Germination Regeneration Ferrulic ac. x X - 80 P. Coumaric ac. X x 100 Salicylic ac. x x 100 100 Gentisic ac. x 100

Chemical control afford treatments achieving a good A wide array of herbicides has been control. Systemic herbicides such as screened for their efficacy on S. trifluralin, pendimethalin, phenoxy acids, elaeagnifolium in concerned countries. clopyralid and bromacil gave a good For example, in Morocco, 102 herbicides control in cropped lands. The two first trials were conducted by researchers from compounds are more effective on 1987 to 2000 (Baye et al., 2007). In seedling and/or germinating seeds. In non contrast to low control achieved in South cropped lands, imazapyr, picloram, Africa and Australia and although the phenoxy acids, glyphosate, sulfosate and species has an exceptional root bromacil may be successfully used. Rates development that makes its control a little and conditions of application of these bit so difficult, some herbicides may herbicides are given in tables 3, 4 and 5.

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Table 3: Herbicides for S. elaeagnifolium control in orchards and sugarbeet

Crops Herbicides Rate Weed stage Observations (g/ha)

Orchards Glyphosate 2160 Full flowering –green -Same conditions as Sulfosate 2880 berry in intercopping strategy

Bromacil 6400- Pre-emergence -Used only in citrus 4 8000 years old Sugarbeet Clopyralid 300 Flowering 2 X 150 3 X 100

Table 4: Herbicides for S. elaeagnifolium control in Cotton

Herbicides Rate (g/ha) Application period

Fluometron (1) 1000-2000 -pre-emergence of crop Trifluralin (2) 2880 -pre-plant of crop Pendimethalin (3) 990 -pre-emergence of crop 2 +1 960 +1000 2 +3 2880 +990

Table 5: Herbicides of S. elaeagnifolium Control in Ruderal Places

Herbicides Rate (g/ha) Weed stage Observation

Imazapyr 625-750 Flowering -add non ionic adjuvant at 0.5%(v/v) 1000-1250 Fruiting -avoïd places with trees Bromacil 6400 -Pre-emergence - avoïd places with -Early post-emergence trees 2.4D ester 1000 Flowering -use soft water 2.4D +MCPA 1000 + 1000 -use two applications Dicamba 2400 /year 2.4D + Dicamba 1720 + 600 MCPP + 2.4D + 1625 +3880 + MCPA 2000

In addition, an intercropping season efficacy is determined by some factors strategy by using glyphosate, sulfosate such as drought stress, dustiness of and amitrole (aminotriazole) was leaves, air humidity and quality of water developed (Table 6). Glyphosate is the (Bouhache et al., 1996). Glyphosate. most commonly used in Morocco. Its (2150 g /ha) added to ammonium 6

sulphate (5%) at green berry stage of the and appeared to be influenced by S. elaegnifolium, and soft water as phonological stage of the weed herbicide carrier gave a successful and (Bouhache et al., 1993) long term control (>90%) during the following season. (Table 7) Total non- In Morocco, the combination of chemical structural carbohydrates (TNC) levels are (mainly glyphosate) and mechanical a good indicator for the period of (summer ploughing) control reduced spraying either systemic or contact density, biomass and fruit production of herbicides. The TNC were lowest at S. elaeagnifolium by >92, >94 and 100%, flower initiation stage and they built up respectively (Zaki et al., 1995). between flowering and fruit maturation,

Table 6: Intercropping season strategy to control S. elaeagnifolium

Herbicide Rate Weed stage Application conditions g/ha

Glyphosate 2160 Full flowering -pre-irrigation 1 week before Sulfosate 2880 to Green berry application -Use 300-400 /ha of soft water -Add Ammonium sulfate at 1.25% -Spray at sunrise (high RH & moderate T°) Aminotriazole 7200 Pre-irrigation (Amitrole)

Table 7: Efficacy of glyphosate based Intercropping strategy

Crops Sowing date Biomass reduction (%) Fruits reduction (Months after sowing harvest (%) treatment) Wheat 2-3 68 94 80 Sugarbeet 2-3 93 94 84 Cotton 8-9 93 83 94

Biological control only three candidates showed host specificity, climatic adaptation. They Adopted within an integrated showed no risk to native Solanum species management framework, biological and promising use, a nematode and two control may be used in combination with insects. specific management practices to keep S. elaeagnifolium under control. There have A foliar nematode parasite ( Orrina been extensive investigations for phyllobia (Thorne) Brzeski = biological agents in USA, South Africa Nothanguina phyllobia Thorne) which and Australia. Although, several attacks S. elaeagnifolium has been biocontrol agents have been investigated, identified and suggested for biological

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control in USA. The nematode causes localized and scarce at few release sites. hypertrophy and hyperplasia of leaves However, L. texana has multiplied, and stem tissues and as consequence become abundant in several sites, reached forms large galls. This biological agent under some circumstances high densities reduces plant density and foliar biomass. and caused considerable damage on the Thus, N. phyllobia is a good candidate fo host plant. The biological agent strips the S. elaeagnifolium in rangelands (Northam leaves, flowers and epidermal tissue from and Orr, 1982). S. elaeagnifolium. As consequences, vegetative growth and fruit production Released in South Africa in 1992 for S. are severely reduced (Offmann et al., elaeagnifolium biological control, two 1988; Olckers et al., 1999). Plants that leaf-feeding chrysomelid beetles have repeatedly been defoliated become Leptinotarsa texana Schaeffer and L. weakened and less or not competitive defecta Stal have been established on S. with pastures or crops. elaeagnifolium. L defecta remains

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