Tropical soda apple (Solanum viarum)

Tropical soda apple is a prickly shrub with white flowers and yellow fruit. It forms dense thickets that quickly outcompete pastures and can restrict livestock movement.

Profile

How does this weed affect you?

Tropical soda apple is a weed that can significantly reduce pasture productivity. It spreads very quickly and:

• can replace one hectare of pasture in 6 months from just a few plants
• forms dense thickets that prevent livestock from accessing shade and water
• has sharp prickles that can injure people and animals
• can be poisonous to people if eaten in large quantities
• outcompetes native plants
• hosts many crop pests and diseases including viruses, fungi and insects that damage fruit and vegetable crops especially tomatoes, potatoes and capsicum.

Each plant produces up to 45 000 seeds per year. In the USA, this plant infested over half a million hectares in just 5 years.

What does it look like?

Tropical soda apple is an upright, branching, perennial shrub growing up to 2 m. In cooler climates with multiple frosts it is an annual plant. It has cream coloured, tapered prickles up to 12 mm long on most parts of the plant.

Leaves are:

• green with cream-coloured veins
• 10–20 cm long and 6–15 cm wide
• divided with 5–7 lobes
• covered in short soft velvet-like hairs
• prickly along the veins especially the main vein.

Flowers are:

• white
• 1.5–2.0 cm wide
• star shaped with 5 pointed petals that curve backwards
• in clusters of 3–6 on a short stem
• present all year round when temperatures are warm enough, but flowering does not occur when night temperatures are 8°C or below regardless of daytime temperatures.

Fruit are:

• round
• 2–3 cm in diameter
• pale green with dark green veins when young (they look like small watermelons)
• yellow and golf ball-size when mature
• abundant, with up to 150 on each plant yearly, each containing up to 400 seeds.

Seeds are:

• reddish brown when mature and white when immature
• 2.5–3 mm wide
• flat
• covered in a sticky coating.

Stems are:

• broad at the base
• branched with cream-coloured prickles to 12 mm long.

Roots are:

• extensive and include lateral roots up to 30 cm deep that spread up to 1.8 m from the base of the plant.

Similar looking plants

Tropical soda apple looks like several other solanum weeds:

• Giant devil’s fig (Solanum chrysotrichum), which is often taller (up to 4 m) and has shorter (2–6 mm) green prickles. Its flowers are in larger clusters of up to 50 flowers,nd the leaves have reddish hairs when young with no hairs on top when mature.
• Devil’s fig (Solanum torvum), which is up to 3 m tall. It does not always have prickles on the leaves and the leaves are not as deeply lobed. Its flowers are in clusters of 15 - 100 rather than just 3-6.
• Devil’s apple (Solanum capsicoides), which has bright red fruit when ripe, yellow prickles and is usually only up to 1 m tall.

More similar species are described in the Tropical Soda Apple Best Practice Manual - see the link in more information below. 

Where is it found?

Tropical soda apple was first identified in Australia in the upper Macleay valley in August 2010. In NSW all infestations are under control programs to eradicate the plant.

Currently infestations are:

• across the North Coast region with dense infestations along the Macleay and Clarence rivers
• in the Northern Tablelands within the upper Macleay valley, near the Gibraltar Range and in Tenterfield Shire
• in the Hunter region on the mid coast.

Tropical soda apple is a native of north eastern Argentina, south eastern Brazil, Paraguay and Uruguay. It has naturalised in the USA, Africa, India, Nepal, West Indies, Honduras, Mexico, and outside its native range in South America. In Australia it is also present in Queensland.

What type of environment does it grow in?

Tropical soda apple grows in tropical, subtropical and temperate climates. Plants grow best in areas that have rainfall between 700 and 2000 mm per year.

Tropical soda apple:

• can grow in a variety of soil types but grows best in well-drained soils with high levels of organic matter and available phosphorous
• will tolerate saline soils
• is not tolerant of extended periods of waterlogging, dying if waterlogged for more than three weeks
• will tolerate some frost however, leaves will be damaged, and flowering and fruiting will stop (leaves may reshoot after two weeks)
• can survive dry conditions and responds by dropping leaves
• is tolerant of some shade but prefers to grow in full sun

Note that fruit that remains on plants effected by waterlogging or dry conditions may still contain viable seeds.

Plants have been found growing:

• in pastures
• along waterways and on flood plains
• along roadsides
• in open woodlands and the edge of forests
• in horticultural and cropping areas.

Maps and records

• Recorded presence of Tropical soda apple during property inspections (Map: Biosecurity Information System - Weeds, 2017-2024)
  These records are made by authorised officers during property inspections under the Biosecurity Act 2015. Officers record the presence of priority weeds in their council area and provide this to the NSW Department of Primary Industries. Records reflect the presence of the weed on the date of inspection.
  
  

How does it spread?

By seed

Tropical soda apple plants can produce fruit 75 days after germinating. Plants may produce thousands of seeds per plant per year. The seed has high viability and germination rates are often over 90% and as high as 100%. Most seed sprouts within 24 months of the fruit splitting. Seeds passing through an animal are more likely to germinate.

Seeds are viable in:

• ripe (yellow) fruit over 1 cm in diameter
• immature green fruit over 1.5 cm

In NSW most seed are spread by cattle. They seek out and eat the sweet-smelling fruit and spread seeds in their manure. Infestations have been found by tracing cattle movements from infested properties using the National Livestock Identification Scheme database. Other animals that eat and spread the seeds include:

• horses
• feral deer
• rodents
• birds
• pigs.

 Seeds are also spread:

• in water, especially flood water as the fruit can float
• in contaminated fodder
• in contaminated soil
• by sticking to vehicles or machinery.

By plant parts

Tropical soda apple can regenerate from root and stem material which can be moved by machinery or poor disposal. 

References

Akanda R.U., Mullahey J.J., Shilling D.G., (1996). Environmental factors affecting germination of tropical soda apple (Solanum viarum). Weed Science, 44(3), 570-574.

Bryson, C. T., & Byrd Jr, J. D. (2007). Biology, reproductive potential, and winter survival of tropical soda apple (Solanum viarum). Weed Technology, 21(3), 791-795.

Bryson, C. T., Reddy, K. N., & Byrd Jr, J. D. (2012). Growth, development, and morphological differences among native and non-native prickly nightshades (Solanum spp.) of the south-eastern United States. Invasive Plant Science and Management, 5(3), 341-352.

Call, N. M., & Coble, H. D. (1998). Phosphorus effects on tropical soda apple (Solanum viarum Dunal) growth and development. Southern Weed Science Society (USA).

Mullahey, J. J. (2012). Biology Ecology and Control of Tropical Soda Apple (Solanum viarum). Pakistan Journal of Weed Science Research, 18: 447-456, Special Issue.

PlantNET (The NSW Plant Information Network System). Royal Botanic Gardens and Domain Trust, Sydney. Retrieved 20 January 2021 from: https://plantnet.rbgsyd.nsw.gov.au/cgi-bin/NSWfl.pl?page=nswfl&lvl=sp&name=Solanum~viarum 

Trenholm, L. E.; Sturgis, A. K.; Ninaji, A.; Gallaher, R. N.; Akanda, R. U.; Mullahey, J. J. (1995). Growth and nutrient accumulation in tropical soda apple (Solanum viarum Dunal). Agronomy Research Report AY-95-04. Gainesville, FL: University of Florida, Department of Agronomy. 27 p

van Driesche R et al. (2002). Biological control of invasive plants in the eastern United States, USDA Forest Service.

Welman, W. G. (2003). The genus Solanum (Solanaceae) in southern Africa: subgenus Leptostemonum, the introduced sections Acanthophora and Torva. Bothalia, 33(1), 1-18.

More information

back to top

Control

Successful weed control requires follow up after the initial efforts. This means looking for and killing regrowth or new seedlings. Using a combination of control methods is usually more successful.

If you find tropical soda apple, contact your local council weeds officer as soon as possible for advice and assistance to eradicate it from your property. Tropical soda apple grows quickly and seeds prolifically. A few plants can form a hectare sized thicket in six months. Inappropriate control efforts can accidentally spread this weed.

To manage tropical soda apple:

• seek advice on the control of mature plants as soon as you become aware of them
• check stock quarantine areas for new seedlings emerging from dung 1 to 2 weeks after the quarantine, and kill any seedlings
• check for new plants in spring and summer
• kill plants before they are 2 months old to prevent fruit and seed set
• collect and dispose of fruit to reduce seedling numbers.

Prevention

Hold new cattle for 6 days

To mitigate the very high risk of introducting this plant, any new cattle coming onto any property must be held for 6 days, in an area that can be closely inspected for seedlings. Tropical soda apple seeds become ready to sprout when they are eaten by cattle and passed within 6 days. After 6 days, any seeds that are passed won't sprout. Studies of seed viability after being consumed by horses have not yet been done, and any new horses coming onto a property should also be held for 6 days in an area that can be checked for seedlings. 

Rotational paddocks, holding paddocks, quarantine paddocks or electric-fenced areas are all suitable, and must be checked regularly for the presence of seedlings. Plants can produce fruit within 2 months of germinating.  

Hold stock before sale or movement

Hold livestock in a paddock free of tropical soda apple for at least 6 days before selling them or moving them off your property.

Livestock movements and the law

It is illegal to knowingly transport the seeds of this plant inside an animal, or to knowingly buy or sell an animal that contains seeds. The movement of seed in cattle is traceable, and knowingly moving seeds in animals, or buying or selling animals containing seeds can result in prosecution and fines

Check your property regularly

Check your land as often as possible, particularly during spring and summer. Check:

• cattle camps, stock yards, feed-out areas and holding paddocks
• waterways, drains, gullies, floodplains, flats and areas with flood debris
• fence lines, tracks and roads
• forested areas and areas where feral animals may have been.

Check all control sites every 2 months.

Physical Control

By Hand

Small plants and plants in soft soil can be pulled or dug out with a hoe or mattock. Plants need to be disposed of so that they do not reshoot from seeds or stems. Wear gloves or use pliers to grip the stems to avoid injury from prickles.

Disposal

Plants can be burnt in a hot fire. Check the burnsite regularly for any seedling growth. If storing fruit, keep it in a container away from soil, flood zones livestock and vermin.

Contact your local council for other appropriate disposal methods.

Chemical control

Spraying

Spraying is effective and especially suitable for dense infestations. Ensure that all the leaves are covered in the herbicide. Use appropriate herbicides if plants are near waterways. Ensure that a wetter is added to the herbicide mix.

Herbicides kill the plants, but do not kill the seeds inside the fruit. All fruit must be removed by hand, even small green fruit can have viable seeds.

Cut stump

Large scattered plants can be controlled by the cut stump method. Cut the stem close to the ground and then apply the herbicide within 10 seconds to the stem left in the ground.

If using gel type herbicide, apply a 3-5 mm layer of gel for stems less than 20 mm. Apply a 5 mm layer on stems above 20 mm. Liquid herbicides can be painted onto the stem.

Dispose of the cut plant and any fruit after treating the stump.

Herbicide options

See Using herbicides for more information.

---

PERMIT 9907 Expires 31/03/2025
Glyphosate 360 g/L (Various products)
Rate: 200 mL in 10 L of water
Comments: Spot spray application
Withholding period: Nil.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
Resistance risk: Moderate

---

PERMIT 9907 Expires 31/03/2025
Glyphosate 360 g/L (Various products)
Rate: 1 part per 1.5 parts of water
Comments: Cut stump application
Withholding period: Nil.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
Resistance risk: Moderate

---

PERMIT 12942 Expires 30/08/2025
Glyphosate 360 g/L with Metsulfuron-methyl 600 g/kg (Only products registered for aquatic use)
Rate: 2 L glyphosate plus 10g of metsulfuron in 100 L of water
Comments: A wetter must be used at a rate of 500 mL per 100 L. Apply a maximum of 2 times per year at a minimal interval of 60 days. Ensure spray covers all foliage and stems as incomplete application will result in regrowth.
Withholding period: Nil.
Herbicide group: 9 (previously group M), Inhibition of 5-enolpyruvyl shikimate-3 phosphate synthase (EPSP inhibition)
Resistance risk: Moderate

---

PERMIT 12942 Expires 30/08/2025
Picloram 100 g/L + Triclopyr 300 g/L + Aminopyralid 8 g/L (Grazon Extra®)
Rate: 350 to 500 mL in 100 L of water
Comments: A wetter must be used at a rate of 500 mL per 100 L. Apply a maximum of 2 times per year at a minimal interval of 60 days. DO NOT use products containing picloram and triclopyr within 5 m of a waterway. Ensure spray covers all foliage and stems as incomplete application will result in regrowth.
Withholding period: Where product is used to control woody weeds in pastures there is a restriction of 12 weeks for use of treated pastures for making hay and silage; using hay or other plant material for compost, mulch or mushroom substrate; or using animal waste from animals grazing on treated pastures for compost, mulching, or spreading on pasture/crops.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

---

PERMIT 12942 Expires 30/08/2025
Triclopyr 300 g/L + Picloram 100 g/L with Metsulfuron-methyl 600 g/kg (Various products)
Rate: 350 to 500 mL plus 10g metsulfuron in 100 L of water
Comments: A wetter must be used at a rate of 500 mL per 100 L. Apply a maximum of 2 times per year at a minimal interval of 60 days. DO NOT use products containing picloram and triclopyr within 5 m of a waterway. Ensure spray covers all foliage and stems as incomplete application will result in regrowth.
Withholding period: Nil.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

---

Picloram 44.7 g/L + Aminopyralid 4.47 g/L (Vigilant II ®)
Rate: Undiluted
Comments: Cut stump application. Apply a 3-5 mm layer of gel for stems less than 20 mm. Apply a 5 mm layer on stems above 20 mm.
Withholding period: Nil.
Herbicide group: 4 (previously group I), Disruptors of plant cell growth (Auxin mimics)
Resistance risk: Moderate

---

back to top

Biosecurity duty

The content provided here is for information purposes only and is taken from the Biosecurity Act 2015 and its subordinate legislation, and the Regional Strategic Weed Management Plans (published by each Local Land Services region in NSW). It describes the state and regional priorities for weeds in New South Wales, Australia.

Area	Duty
All of NSW	General Biosecurity Duty All pest plants are regulated with a general biosecurity duty to prevent, eliminate or minimise any biosecurity risk they may pose. Any person who deals with any plant, who knows (or ought to know) of any biosecurity risk, has a duty to ensure the risk is prevented, eliminated or minimised, so far as is reasonably practicable.
All of NSW Tropical Soda Apple Control Zone: Whole of NSW	Control Order Tropical Soda Apple Control Zone (Whole of NSW): Owners and occupiers of land on which there is tropical soda apple must notify the local control authority of new infestations; destroy the plants including the fruit; ensure subsequent generations are destroyed; and ensure the land is kept free of the plant. A person who deals with a carrier of tropical soda apple must ensure the plant (and any seed and propagules) is not moved from the land; and immediately notify the local control authority of the presence of the plant on the land, or on or in a carrier.

back to top

Reviewed 2024