Quick Facts

Quick facts

What Does It Look Like?

What is it?

Silver-leaf Nightshade (Solanum elaeagnifolium) is a long-lived suckering herb up to 06–1 metre tall. Its roots are deep (up to 2 metres), and while the upper parts of the plant may die off each year, the roots remain viable and produce new plants each season. Individual plants are variable with respect to prickliness, leaf margin, hair colour and flower colour. The stems and leaves are usually densely covered with whitish stellate (star-shaped) hairs on both surfaces, giving it the silvery-white appearance of the common name. There are also populations which have a rusty green appearance, but these are less common. Stems usually have slender, 2–5 mm long, reddish or yellow spines which also sometimes occur on the leaf veins. Leaves have a petiole (stalk) up to 1 cm long lengthening to 20–30 mm in fruit. The oblong to long lance-shaped leaves are 20-100 mm long and 10-30 mm wide, with the upper leaves having wavy margins and lower ones sometimes shallowly lobed. 

Flowers are 20–40 mm diameter and are blue rarely white, pink or purple, on a stalk up to 10 mm long; they are a typical star-shaped "Solanum" flower of 5 fused petals with 5 conspicuous yellow stamens, the latter 7–8 mm long.

Fruits are berries, globular, green with darker green markings when immature, ripening to yellow or brownish and up to  14-15 mm diameter.  Shoots produce about 60 berries per season in Australia and each berry contains about 50 tomato-like Seeds (Heap and Wu 2018) that are flat, brown to light brown in colour and up to 4 mm long. (Navie 2004; Purdie et al. 1982; Washington State Noxious Weed Control Board 2007).

Recognition: This species can normally be recognised by the combination of the following characters; silvery foliage with leave that have a wavy margin; spines normally on stem and main leaf veins; fruit with green striate marking, green while unripe, turning orange when ripe; plant dies back to ground level sometimes leaving main stem with dry fruit.

For further information and assistance with identification of Silver-leaf Nightshade contact the herbarium in your state or territory.

Flower colour

Blue and White or Purple and White.

Growth form (weed type/habit)

Herb

Where it currently grows? Preferred habitat

Silver-leaf Nightshade is a weed of cultivation and of disturbed and waste areas (Navie 2004). In Australia it is found in semi-arid, temperate and sub-tropical regions (Navie 2004) and in rainfall areas of 250 to 600 mm (Parsons and Cuthbertson 1992), considerably higher than those cited above for American conditions. It is also establishing in higher rainfall areas on the urban fringes around Adelaide in South Australia (Chris Brodie pers. com. 2020). The plant does not appear to have any soil preferences in Australia but in the Americas it is recorded from coarse-textured, sandy soils.

Are there similar species?

Silver-leaf Nightshade is a member of the very distinctive Solanum group of plants and shares with the rest of the members of the genus the very distinctive Solanum flower shape (e.g. potatoes, tomatoes, capsicums) with 5 star-shaped petals with 5 prominent yellow stamens at right-angles to the petals.

However there are some 180 species of Solanum in Australia, many of them native and so care needs to be taken in identification, particularly as many of the native species may also occupy roadside and other areas of disturbance and look superficially similar. The silvery appearance may be helpful but because there are so many similar species it is best that confirmation of an identification of Silver-leaf Nightshade is made by your local weeds officer or by the herbarium in your state or territory.

Why Is It A Weed?

What are its impacts?

Silver-leaf Nightshade is a Weed of National Significance (WoNS). It is regarded as one of the worst weeds in Australia because of its invasiveness, potential for spread, and economic and environmental impacts on agriculture and primary production.  It is estimated that silverleaf nightshade probably causes losses to Australian agriculture of around $80M each year (Heap & Wu 2018).

Agriculture: Silver-leaf Nightshade impacts crops and pastures reducing yields through competition for nutrients and water,  and is difficult to manages so reducing land values.  It can also exude plant growth inhibitors, interfere with animal husbandry and harvesting practices, and is an alternative host for plant eating insects and plant diseases and their vectors (Heap & Wu 2018).  It is actively spreading in the cereal areas of southern Australia and has the potential to spread much more widely. It significantly lowers crop yield (Lemerle & Leys 1991; Hawker 2004) in winter cereal-growing areas and also affects such crops as cotton, sorghum, maize and lucerne. The food reserves in its root system and the ability of the roots to grow deeper than those of most crops allow it to establish itself earlier than any crop it is competing with (Washington State Noxious Weed Control Board 2007), and because it is summer-growing it depletes nutrients for later sown winter crops. Silver-leaf Nightshade may support populations of pests harmful to other Solanaceous crops (Washington State Noxious Weed Control Board 2007) such as potatoes, capsicums, tomatoes and eggplants.

Silver-leaf Nightshade may also have allelopathic effects in cotton (Parsons & Cuthbertson 2001). The spiny leaves and stems contaminate hay made from infested paddocks (Washington State Noxious Weed Control Board 2007).

Fruits can be toxic to some livestock. Cattle are more likely to be affected than sheep while goats are not affected at all (Washington State Noxious Weed Control Board 2007). Hawker (2004) reports the successful use of sheep and goats for suppressing growing shoots, but stock was not introduced to paddocks where fruits were present on plants in that study.

The Australian cereal cropping zone hosts a range of valuable major enterprises that are at risk from Silver-leaf Nightshade, including production of cereals (e.g. wheat, barley, triticale, oats), pulses (e.g. peas, beans, lentils, lupins, vetch), oilseeds (e.g. canola), hay, grazing (e.g. sheep, cattle), and myriad minor enterprises. In addition, horticultural enterprises such as wine, vegetable and fruit production are at risk. (Heap & Wu 2018)

Native ecosystems: Carr et al. (1992) suggests that it is not a weed of natural ecosystems, but this may be due to lack of opportunity to this time as recent observation indicate it can spread into and grow in open vegetation in semi-arid environments (Chris Brodie pers. com. 2020).

Urban areas: Known to spread along roadsides and fire breaks and under power-lines, it is also a weed of grassy areas in towns and cities.  Spines on plants may induce an allergic reaction in some people (Botanical Dermatology Database 1994 -). Whether fruits are toxic to man appears not to be documented but American Indians of south-western parts of the United States have used the fruits for converting milk to cheese and they have also used them in tanning of hides (Boyd et al. 1984).

How does it spread?

Silver-leaf Nightshade can spread by seed, by suckering, and by re-sprouting from the perennial roots, either in situ or from broken off pieces of root. 

Spread by seeds: Establishment of new Silver-leaf Nightshade infestations on clean land overwhelmingly originate from seeds ingested by livestock, mostly sheep and cattle. Silver-leaf Nightshade invasion at the district level typically begins with one roadside or paddock infestation, usually from seed. There are other invasion pathways but sheep, in particular, are the main vector for seeds (Heap & Wu 2018). Establishment of new Silver-leaf Nightshade infestations on clean land overwhelmingly originate from seeds ingested by livestock and seed excretion peaks about 24 hours after ingestion, and then there is a steady decline over seven days to a low level (Heap & Wu 2018). Sheep eat mature berries, and viable seeds may then be deposited in dung for the next two to three weeks (Heap & Wu 2018). Birds and other animals: Most information on wildlife as vectors is anecdotal and difficult to confirm. In any case, these are likely to be minor vectors compared to sheep. It is likely that birds spread seed. Water, soil and wind: Mature berries float in water and new infestations can arise downstream in irrigated land, creeks, drainage lines and wash ways (Heap & Wu 2018). Agricultural seeds and fodder: Regional opinion around Australia often suggests that Silver-leaf Nightshade was introduced to various areas in the early part of the 20th century as a contaminant of sowing seed or fodder. It is difficult to verify these claims, but Silverleaf Nightshade berries are found as a contaminant of some agricultural grains and hay.

Horizontal roots: Underground spreading roots can give rise to new plants some distance from the original. Creeping lateral root growth of Silver-leaf Nightshade can spread 1 to 2 m per year via creeping horizontal lateral roots. This is usually of minor importance, except where colonies grow under fence lines and allow livestock in adjoining clean paddocks to access and spread the berries, or occurs over 30 to 40 years when  a whole paddock can be covered as many individual patches grow into each other (Heap & Wu 2018).

Vegetative spread: Spread via root and stem fragments occurs when soil cultivation break up root fragments and these are dragged within a paddock, or to nearby paddocks. This is most likely to occur with the use of cultivators and deep seeding points. Long-distance spread is possible if contaminated machinery is transported to other areas and then used within a few weeks (Heap & Wu 2018). Root fragments possess small dormant growth buds that are activated when broken from the parent plant. The buds produce new roots and shoots, using energy and moisture stored in the fragment and soil.

Another vector of spread as noted by Heap and Wu (2018) is Machinery and vehicles: Contaminated machinery and vehicles are not likely to be significant vectors for Silverleaf Nightshade, but good machinery and vehicle hygiene are a fundamental part of any comprehensive farm bio-security plan;

In the United States, individual berries produce 24 to 149 seeds, which can add up to 5 million to 100 million seeds per acre (0.4 ha). These seeds may be dispersed by cultivation, by wind, water, machinery, agricultural produce or in animal droppings (some studies indicate that 10% of seed remain viable after passing through sheep).  Dead plants being blown about like tumble-weeds can also spread seed (Washington State Noxious Weed Control Board 2007). Birds may also be responsible for dispersing seeds.

What is its history in Australia?

By the late 1900s Silver-leaf Nightshade was known from Australia, Egypt, Greece, India, Israel, Zimbabwe, Sicily, South Africa, Morocco and Spain (Washington State Noxious Weed Control Board 2007). It was first recorded at North Melbourne in 1909 (Smith & Faithfull 1998; Parsons & Cuthbertson 2001) and a little later for South Australia (Kloot 1986). However, its weedy potential was not recognised until the 1940s.

How To Manage It?

Best practice management

Silver-leaf Nightshade is extremely difficult to control and so the best prevention is early eradication of plants as soon as they are recognised. Animals should not be allowed to eat fruiting plants, not only because the fruits can be poisonous, but also because it can increase seed dispersal. Vehicles and machinery need to be thoroughly cleaned. Recent studies (Hawker et al. 2006) have shown that there is a great deal of genetic diversity within the South Australian populations and that seeds seem to play the major role in spreading this plant. There are three major goals when managing dense, established infestations: 1) Prevent seed production. 2) Kill shoots during summer/ autumn to protect following crop and pasture yield. 3) Reduce the size and vigour of the root system over time (Heap & Wu 2018).

Chemical control: Silver-leaf Nightshade can be difficult to control with herbicides because of the horizontal root system from which new plants are able to establish. Glyphosate and picloram have been found to be effective in other countries. For effective control with chemicals foliar application is required with numerous applications need over 3-5  years to exhaust the root system. For a list of herbicides and methods for use in Australia see Heap and Wu (2018); Smith & Faithfull (1998) . Also see the Australian Pesticides and Veterinary Medicines Authority for chemical information http://www.apvma.gov.au .

Non-chemical control: Physical control: Manual (hand) removal or Mechanical (machine removal) is not recommended as roots are deep (up to metres deep) and need to be removed as new plants can grow from the smallest root fragment. Mechanical control that disturbed the roots will only spread roots and stimulate growth of new plants.

Cultivation: The ability of Silver-leaf Nightshade plants to re-sprout has meant that mowing or cultivation of the ground is not an option as this disturbed and spreads root fragments which are also capable of producing new plants.

Vigorous crops and pastures, especially those based on perennial summer-growing species can significantly suppress Silverleaf Nightshade growth (Heap and Wu 2018). Shading provided a crop canopy could be used a control mechanism in small patches, provided a crop canopy could be established before the plant matures (Washington State Noxious Weed Control Board 2007). Given that Silver-leaf Nightshade generally has a competitive advantage this can be difficult to achieve and this method is not likely to be useful in Australia's broad-acre farming areas, although a crop of Lucerne may be useful in this regard (Smith & Faithfull 1998).

Grazing: by sheep and goats could "reduce the size and number of Silver-leaf Nightshade shoots during the growing season, as well as suppressing flowering and seed set" (Hawker 2004). However, cattle and sheep should not be allowed to eat fruiting plants, not only because the fruits can be poisonous, but also because it can increase seed dispersal. Establishment of new Silver-leaf Nightshade infestations on clean land overwhelmingly originate from seeds ingested by livestock that have eaten ripe fruits. Animals  should be quarantined in a holding zone /paddock in for 7 days before being transport to other areas free of Silver-leaf Nightshade to help reduce risk of spread. The vast majority of seeds pass through animals with 7 days but some may still are excreted  2-3 weeks after ingestion.

Disposal: Any roots that are dug up should be disposed of as root fragments can produce new plants if left in or on the soil.

Biological control: Silver-leaf Nightshade has also been recognised as a target for biological control through a cross-jurisdictional government process. This allows activities to be undertaken to develop effective biological controls. A leaf galling nematode was tested as a biological control agent in Victoria in the 1980s but because it was found to affect other Solanum species grown as crops it was not able to be released. Other biological control agents have been tested but were also found to impact closely related crop plants. No biological agent is available in Australia.

Does it have a biological control agent?

NO

When does it grow? (lifecycle/growth calendar)

Silver-leaf Nightshade is a summer-growing perennial plant, with an extensive root system. Seeds germinate in autumn and there is a concentration on root growth initially. Roots can grow very deep (up to 2 metres) and extend horizontally d 1 to 2 metres per year via creeping horizontal lateral roots to produce new shoots at a distance the parent plant.  New shoots emerge from the horizontal roots in spring and plants begin flowering by November, continuing into summer. Fruits are produced in the summer months. Above ground parts of the plant die back at the end of summer but the dried plants with their attached fruits are persistent for some time (Parsons & Cuthbertson 2001).

Where Is It Found?

Which states and territories is it found?

ACT, NT, NSW, QLD, SA, VIC, WA

What areas within states and territories is it found?

Silver-leaf Nightshade is a widespread species found in cereal-growing area of southern Australia. It also occurs in south-eastern Queensland and there are some herbarium records from inland South Australia, Victoria, NSW, Western Australia, and at least one record from the Northern Territory. Silver-leaf Nightshade is spreading in the cereal areas of southern Australia and Western Australia. Current herbarium records indicate that it has the potential to spread much more widely than originally thought (AVH 2020; Barker pers. comm. 2007).  It is not recorded from Tasmania.

Where does it originate?

For many years it had been unclear whether Silver-leaf Nightshade originated in North America or South America but recent DNA studies have shown its relationships lie with other Mexican and southern USA species of Solanum and so this is likely to be its area of origin, with  and recent studies confirming that Silver-leaf Nightshade is probably native to the Monterrey region of north-eastern Mexico (Heap & Wu 2018). Early American colonists were presumably responsible for its spread outside this region into other areas of the Americas (Levin et al. 2006).  It is now a weed in may areas outside it native range.

National And State Weed Listings

Is it a Weed of National Significance (WONS)?

YES

Where is it a declared weed?

Declared in all Australian states and territories

Government weed strategies and lists – Weeds Australia

Is it on the National Alert List for Environmental Weeds?

NO

Government weed strategies and lists – Weeds Australia

Is it on the Agricultural Sleeper List?

NO

Government weed strategies and lists – Weeds Australia

Names And Taxonomy

Main scientific name

Solanum elaeagnifolium

Other scientific names (synonyms)?

Does it have other known common name(s)?

White Horse-nettle, Tomato Weed, White Nightshade, Bull-nettle, Prairie-berry, Satansbos, Silver-leaf Bitter-apple, Silverleaf-nettle, Trompillo.