Title: Solanum elaeagnifolium Cav.




Description

Appearance Herbaceous plant - Forb (flowering herbaceous plant - not a grass)
Properties Silverleaf nightshade is an erect summer perennial herb growing to a height of 80 cm.
Stems Stems of silverleaf nightshade are erect with many branches and densely covered with fine star-shaped (stellate) hairs which give them a silver-white appearance. They also usually have numerous slender, yellow to red prickles 2-4 mm long.
Leaves Silvery white due to a dense covering of stellate hairs and denser on the under surface. Alternate, lanceolate to oblong, growing to 15 cm long (usually about 6-10 cm) and 1-2 cm wide. Stalked, often with prickles on the underside of veins with undulating margins and often scalloped
Flowers Silverleaf nightshade flowers are purple to violet or occasionally white and grow to 3.5 cm in diameter. They consist of five fused petals with five yellow, long and tapering anthers.
Fruit

The fruit of silverleaf nightshade is a smooth globular berry.

They are green with dark striations when immature, yellow and orange mottled and becoming wrinkled and dry when ripe. Fruit are about 1.5 cm in diameter with up to 60 fruits per plant.
Preferred habitat Silverleaf nightshade prefers warm-temperate regions where it is not confined to any particular soil type. It grows well in areas with an annual rainfall of 250-600 mm. The weed is also drought tolerant.
Distribution It is found mainly in areas with an average annual rainfall of 300-560 mm and appears to favour light, textured soils. Larger infestations are found on wheat growing lands and pastures.
Source  
   


World map for Solanum elaeagnifolium
Present Distribution - Australia (source: ALA)

Present Distribution - World (source CABI)




Invasiveness Assessment

ESTABLISHMENT


1.Germination requirements? Seeds germinate in autumn in Australia. P & C (1992 p. 610)


2. Establishment requirements? Establishes in open areas (i.e. pastures and crops). P & C (1992 p. )

3. How much disturbance is required? Invades pastures and crops “Perennial pastures do not check its growth”. P & C (1992 p. 611)

GROWTH / COMPETITIVE


4. Life form? Perennial herb. Other. P & C (1992 p. 609)

5. Allelopathic properties? “It has been suggested that germination may be inhibited by the mucilaginous material surrounding the seed either because it forms a physical barrier to water imbibition or it contains a germination – inhibiting chemical”. “Allelopathic effects have been demonstrated in cotton”. ( P & C 1992 p. 611).

6. Tolerates herb pressure? Consumed by cattle, sheep and goats. However, probably not preferred due to its highly toxic properties. P & C (1992 p. 611)

7. Normal growth rate? “Competes directly with summer-growing crops and pastures and reduces production of winter crops such as cereals”. P & C (1992 p. 611)

8. Stress tolerance to frost, drought, w/logg, sal. etc? Tolerant of drought. (See distribution in P &C 1992 p. 609). “Not confined to any particular soil type”. P & C (1992 p. 609).

REPRODUCTION


9. Reproductive system? “Reproducing by seed and from roots”. P & C (1992 p. 609)

10. Number of propagules produced? About 75 seeds in each fruit x 30 fruits per plant = 2,250 seeds per plant P & C (1992 p. 609-610)

11. Propagule longevity? “Seeds are … long lived”. P & C (1992 p. 611)

12. Reproductive period? Perennial herbs: aerial growth dies at end of summer, but new shoots are produced each spring. P & C (1992 p. 610)

13. Time to reproductive maturity? “Seeds germinate in autumn…flowering commences in November”. P & C (1992 p. 610)

DISPERSAL


14. Number of mechanisms? Numerous - including birds.’ (P & C 1992 p. 611). Sheep are the most significant means of spread in Australia (via ingested seed and long-distance transport). It is also possible for seed to spread in contaminated hay. (John Heap, pers. com. 2012)

15. How far do they disperse? Birds could disperse seeds > 1 km


Impact Assessment

RECREATION


1. Restrict human access? “An erect summer-growing perennial herb, commonly 30 to 45 cm high.” The low growth habit would not restrict human access. P & C (2001)

2. Reduce tourism? “The stems are usually armed with numerous slender prickles 2 to 4 mm long. Aerial growth dies at the end of summer but the dead stems usually remain standing for several months.” The prickly property of the plant may affect some recreational activities.P & C (2001)

3. Injurious to people? See comment in 2 above. Prickles present for much of the year. Potential for minor injury. P & C (2001)

4. Damage to cultural sites? Dense patches may create a negative visual impact. P & C (2001)

ABIOTIC


5. Impact flow? Terrestrial species. P & C (2001)

6. Impact water quality? Terrestrial species.P & C (2001)

7. Increase soil erosion? Root system comprises deep, much branched, vertical and horizontal roots to 2 metres deep and wide. However, aerial growth dies at the end of summer leaving bare areas of soil. Potential for moderate probability of large scale soil movement. P & C (2001)

8. Reduce biomass? “An erect summer-growing perennial herb, commonly 30 to 45 cm high. Silverleaf nightshade competes directly with summer-growing crops and pastures.” Replaces biomass. P & C (2001)

9. Change fire regime? “In Victoria…it usually occurs in discrete patches.” Although aerial growth dies at the end of summer and dead plants remain standing, the plant would not influence fire regime. P & C (2001)

COMMUNITY HABITAT


10(a) Impact on composition of high value EVC? EVC=Plains grassland (E); CMA=North Cental; Bioreg=Victorian Riverina; VH CLIMATE potential. A weed of open pasture/cropping situations. Not known in natural ecosystems in Victoria. Minor displacement of grasses/forbs P & C (2001)

10(b) Impact on medium value EVC? EVC=Grassy dry forest (D); CMA=North Cental; Bioreg=Goldfields; VH CLIMATE potential.
Impact as in 10(a) above. P & C (2001)

10(c) Impact on low value EVC? EVC=Grassy dry forest (LC); CMA=Goulburn Broken; Bioreg=Highlands – Northern Fall; VH CLIMATE potential. Impact as in 10(a) above. P & C (2001)

11. Impact on structure? Primarily a weed of cropping, it also occurs in summer-growing pasture and, “ perennial pasture does not check its growth.” The extensive root system enables the plant to draw moisture and nutrients from a large volume of soil and thus compete effectively against other species. Although it infests broad areas, the infestations tend to be populated as discrete patches. Infestation aided by cultivation. Minor effect on 20–60% of the floral strata. P & C (2001)

12. Effect on threatened flora?

FAUNA


13. Effect on threatened fauna?

14. Effect on non-threatened fauna? Primarily a weed of agriculture. Limited threat due to fauna not co-existing within infested area.P & C (2001)

15. Benefits fauna? “Birds and animals eat the fruit.” Minor food source. P & C (2001)

16. Injurious to fauna? “Feeding trials have confirmed that all parts of the plant, but particularly the fruit either green or ripe, is toxic to animals.” P & C (2001)

PEST ANIMAL


17. Food source to pests? “Birds and animals eat the fruit.” Possible limited food source for minor pest animals. P & C (2001)

18. Provides harbor? A summer-growing perennial. Not known to provide harbor. P & C (2001)

AGRICULTURE


19. Impact yield? “Silverleaf nightshade competes directly with summer-growing crops and pastures, and reduces production of winter crops such as cereals because of the depletion of nutrients and moisture from the soil in the previous summer. In Texas…it considerably reduces cotton and grain sorghum yields.” Major impact on yield. P & C (2001)

20. Impact quality? “…the plant’s spiny leaves and coarse stems may lower the quality of hay taken from infested areas.” Contaminated hay may be rejected for sale outside infested area. WSNWCB

21. Affect land values? “Silverleaf nightshade is one of the most difficult weeds to kill.” The value of land infested with this plant would be reduced due the weed’s persistence and its potential impact on agricultural production. P & C (2001)

22. Change land use? In cropping situations, land use may not need to change depending upon the impact on production. In pasture situations, however, as “sheep are more resistant to the toxins and goats are unaffected,” choice of grazing animal may change. WSNWCB

23. Increase harvest costs? Not known to affect harvest costs

24. Disease host/vector? None evident


Management



Management principles



Invasive plants (weeds) may be managed using a variety of methods. The most effective management is usually achieved through a combination of techniques.

In general, the principles of a successful weed management program are:



Things to consider before you begin

It is important not to disturb native vegetation, culturally significant areas or waterways when undertaking weed control works. You will need to consult with the responsible authority to seek advice on the best approach for your circumstances.

Work with your neighbours and encourage everyone to work together to control weeds at the same time. This will help to reduce re-infestation from neighbouring properties and reduce the amount of follow up control work required.

Contact your local weed/environment authorities and/or community groups who will be able to provide advice and information that will assist your weed management program.

A long-term approach, regular monitoring and vigilance is necessary to successfully control weeds and many years of follow-up management may be required. This is because many weeds will regrow from seed and other plant parts stored in the soil.

Always remember to “manage your weeds before they seed”.

Physical Removal



Physical removal aims to remove the entire plant, including its roots, from the soil, therefore reducing the above-ground plant-mass before follow up methods are applied. This can be achieved by ‘grubbing’ out by hand or, if the plant is large enough, removal by machinery, e.g. tractor and chain, bobcat, or excavator fitted with a grab bucket. All root systems should be removed, as some plants will re-shoot from roots left in the ground. Removal by hand is only suitable for small-scale infestations.

Before undertaking physical removal of weeds you should check for the presence of hazards such as underground cables and take steps to minimise problems that may be caused by erosion or further spread of weed seeds from machinery used in the process.

If any control is to be undertaken which may result in any disturbance of native vegetation, culturally significant areas or waterways, you should contact the responsible authority prior to works being conducted.

Do no transport noxious weeds off your property. Before undertaking physical removal you must consider appropriate disposal of the weed material. Talk to your local authority for disposal advice.

Competitive Planting

Competitive crops and pastures Silverleaf nightshade can be effectively suppressed by crop and pasture competition. Competitive winter crops and their stubble can delay emergence, however silverleaf nightshade will emerge during summer if there is no active competition for summer rainfall. Delaying emergence will promote uniform flowering, making seedbank management operations more efficient. The choice of summer active crop or pasture species should be driven by what will grow well in your paddock and what will fit into your long term planning for that infested paddock.
Aim to maintain pasture biomass above 1.5 t/ha over summer. Manage stocking rates so that grazing occurs for short periods (several days to weeks) to utilise pastures quickly, but then give the pastures time to regenerate (one or two months) before grazing again (Wu).

Competition from the perennial sub-tropical pasture species finger grass and digit grass at a field site at Wellington, NSW, Australia, provided 94% suppression of silverleaf nightshade after two seasons (Stanton, Wu and Lemerle, 2011).

Mechanical control

The predominant source of new stems each season is the rootbank, rather than recruitment of new seedlings from the seedbank. Cultivation will damage the upper portion of a mature root system, however even fragments as small as 1 cm are capable of forming a new plant. In areas where cropping or pasture renovation will occur, cultivation should be kept to a minimum to avoid fragmenting the root system. To avoid unintentionally spreading root fragments, ensure that machinery is thoroughly cleaned prior to moving away from the infested area (Wu).

Allelopathy

Several Eucalypt species have been identified that suppress silverleaf nightshade. In appropriate areas, tree belts could be established and used for long term control of small infestations. As well as providing natural control of weeds, tree belts also provide refuge for native fauna and shelter for livestock (Wu).

Biological Control

(Source: CABI 2013) -- In the USA, the native leaf-galling nematode Ditylenchus phyllobius, which is able to kill plants, has been used as an inoculant on weed infestations with some measure of success (Northam and Orr, 1982). Although several countries have considered classical biological control of S. elaeagnifolium, only South Africa has imported, tested and released biocontrol agents. This has been largely because of concerns about possible attacks on non-target Solanum species, notably cultivated crops (potato and aubergine), and native species. Indeed, several species have been rejected because of unacceptably broad host ranges during quarantine evaluations (Olckers and Zimmermann, 1991; Olckers et al., 1999). Biocontrol in South Africa currently relies on two leaf-feeding beetles, Leptinotarsa texana and Leptinotarsa defecta, both of which are established following releases in 1992. While L. defecta has remained localized and relatively scarce, with no obvious impact on the weed, L. texana has proved very effective. Indeed, L. texana reaches very high population densities and causes considerable damage to the weed, stunting vegetative growth and fruit-production capacity (Hoffmann et al., 1998; Olckers et al., 1999). Indications are that the beetles have the potential to contribute substantially to the control of the weed, particularly outside cropping areas where chemical and mechanical control methods are not cost-effective.




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Assessment ratings originally made by the Victorian Department of Primary Industries.
The entry of this assessment was made possible through the generous support of The Weed's Network Membership.






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Date: 6 February 2013; 2:31:59 pm Australian Eastern Daylight Time

Author Name: Zheljana Peric
Author ID: zper12