Tropical soda apple (Solanum viarum)

Profile

Impact

Tropical soda apple (Solanum viarum), is an aggressive, prickly, perennial shrub 1–2 m high. It invades open to semi-shaded areas, particularly pastures and riparian zones, but also forests, roadsides, recreational areas, and horticultural and cropping areas. It reduces biodiversity by displacing native plants and disrupting ecological processes. Its foliage is unpalatable to livestock, thus reducing carrying capacities, however cattle eat the fruit and spread viable seeds in manure. Thorny thickets of this plant create a physical barrier for animals preventing access to shade and water. The plant is a host for many diseases and pests of cultivated crops, and it contains solasodine which is poisonous to humans.

Tropical soda apple is spread when cattle eat the fruit or the fruit float and move in water. If not controlled a few plants will form a hectare sized thicket in 6 months, with each plant producing 150 fruit containing 45 000 seeds each year. Herbicides kill the plants, but do not kill the seeds inside the fruit. In the USA, this plant infested over hald a million hectares in 5 years. In NSW it is critical to achieve site-based eradication of this plant before it becomes widespread. 

Distribution

Tropical soda apple is a native of north eastern Argentina, south eastern Brazil, Paraguay and Uruguay. It was first recorded in Florida in 1987 and was known to infest 10 000 ha by 1990 and half a million hectares by 1995. By 2007 it had spread to nine other south eastern states in the USA, where it is now a Federal Noxious Weed. Tropical soda apple has also naturalised in Africa, India, Nepal, West Indies, Honduras and Mexico and outside its native range in South America.

It was first identified in Australia in the upper Macleay Valley in New South Wales (NSW) in August 2010, however it is believed to have been present in this area for a number of years. Subsequent surveys found infestations at Wingham, Grafton, Bellingen, Coffs Harbour, Bonalbo, Casino, Murwillumbah and Wauchope. The smaller infestations have been eradicated and the larger infestations are subject to active control programs. In 2011 infestations were discovered in the Namoi and Border Rivers-Gwydir catchments associated with the movement of cattle from infested coastal areas. Infestations were traced to properties near Tamworth, Attunga and Inverell and are currently the focus of an eradication campaign.

Tropical soda apple has the potential to spread in coastal regions of NSW and Queensland, and inland through cattle movements.

Spread

Tropical soda apple reproduces via seed and can regenerate from root and stem material. The fruit are sweet and cattle will smell and seek them out, spreading viable seed in their manure for up to 6 days after consuming the fruit. After 6 days any consumed seeds that are passed are no longer viable. In NSW cattle movements are currently the major vector of spread and infestations have been found by tracing cattle movements from infested properties using the National Livestock Identification Scheme database. Horses have also been observed to eat the fruit and seedlings have germinated in horse manure. 

Seed is also moved when the pithy fruits float in water, and infestations along waterways and floodzones have occured.

The sticky seeds can also be spread by feral animals and birds that feed on the fruit; and via contaminated fodder, produce, soil and equipment.

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.  

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 for new plants

It is important to find plants early. Checking as often as possible, particularly during spring and summer is critical for finding new plants. Landholders in areas where the plant is known to occur need to be vigilant.

Check cattle camps, stock yards, feed-out areas and holding paddocks.

Check waterways, drains, gullies, floodplains, flats and areas of flood debris.

Check fence lines, forested areas, tracks, roads and feral animal haunts.

If you find tropical soda apple, contact you local council weeds officer as soon as possible for advice and assistance to eradicate it from your property.

Description

Tropical soda apple is an upright, branching, perennial shrub growing to 2 m in height. It has broad-based, straight, cream-coloured prickles to 12 mm long scattered on most plant parts.

Key identification features

  • Leaves are mostly 10–20 cm long and 6–15 cm wide. The upper and lower leaf surfaces are densely covered in short hairs; mid-veins and primary lateral-veins are cream-coloured on both sides of the leaves.
  • Flowers are white, 1.5-2 cm wide, with 5 petals. They occur in clusters of 3–6 off a short stem.
  • Mature fruit are yellow and golf ball-size (2–3 cm in diameter). When immature they are pale green with dark green veins, like immature water melons. In the USA plants produce an average of 45 000 seeds.

Acknowledgements

Authors: Rod Ensbey, John Hosking, Birgitte Verbeek, Tony Cook; Prepared by: Jessica Grantley, Birgitte Verbeek, Elissa van Oosterhout.

References

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

back to top

Control

Landholders who have found this plant must contact their local council weeds officer for assistance with identification, control and eradication. Infestations can be spread by inappropriate control activities.

Landholders in affected areas should focus their efforts on checking for this plant, and holding any new cattle that come onto their properties. 

Herbicide options

WARNING - ALWAYS READ THE LABEL
Users of agricultural or veterinary chemical products must always read the label and any permit, before using the product, and strictly comply with the directions on the label and the conditions of any permit. Users are not absolved from compliance with the directions on the label or the conditions of the permit by reason of any statement made or not made in this information. To view permits or product labels go to the Australian Pesticides and Veterinary Medicines Authority website www.apvma.gov.au

See Using herbicides for more information.


PERMIT 9907 Expires 31/03/2020
Glyphosate 360 g/L (Roundup®)
Rate: 200 mL in 10 L of water
Comments: Spot spray application
Withholding period: Nil.
Herbicide group: M, Inhibitors of EPSP synthase
Resistance risk: Moderate


PERMIT 9907 Expires 31/03/2020
Glyphosate 360 g/L (Roundup®)
Rate: 1 part per 1.5 parts of water
Comments: Cut stump application
Withholding period: Nil.
Herbicide group: M, Inhibitors of EPSP synthase
Resistance risk: Moderate


PERMIT 12942 Expires 30/06/2022
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: Hand gun application, plus wetter
Withholding period: Nil.
Herbicide group: M, Inhibitors of EPSP synthase
Resistance risk: Moderate


PERMIT 12942 Expires 30/06/2022
Picloram 100 g/L + Triclopyr 300 g/L + Aminopyralid 8 g/L (Grazon Extra®)
Rate: 350 to 500ml in 100 L of water
Comments: Hand gun application, plus wetter
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: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


PERMIT 12942 Expires 30/06/2022
Triclopyr 300 g/L + Picloram 100 g/L with Metsulfuron-methyl 600 g/kg (Various products)
Rate: 350 to 500ml plus 10g metsulfuron in 100 L of water
Comments: Hand gun application, plus wetter
Withholding period: Nil.
Herbicide group: I, Disruptors of plant cell growth (synthetic auxins)
Resistance risk: Moderate


Picloram 44.7 g/kg + 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: I, Disruptors of plant cell growth (synthetic auxins)
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 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


For technical advice and assistance with identification please contact your local council weeds officer.
For further information call the NSW Invasive Plants and Animals Enquiry Line on 1800 680 244 or send an email to weeds@dpi.nsw.gov.au

Reviewed 2017