Tropical soda apple

Close up of leaf showing thorns on top.	Tropical soda apple invading pasture.	Tropical soda apple with immature (green) and mature (yellow) fruit.

Tropical soda apple (Solanum viarum) is an aggressive prickly perennial shrub 1-2m high.

It invades open to semi-shaded areas, including pastures, forests, riparian zones, roadsides, recreational areas, horticultural areas and cropping areas. It reduces biodiversity in natural areas by displacing native plants and disrupting ecological processes. Its foliage is unpalatable to livestock, thus reducing carrying capacity. Prickles on this plant restrict native animal and stock grazing and can create a physical barrier to animals, preventing movement 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 was first identified in Australia in the Kempsey area, on the Mid North Coast of NSW in August 2010. However, this weed is believed to have been present in this area for a number of years. The current extent of that infestation is about 50ha. Subsequent surveys have identified other smaller infestations in surrounding areas, including Wingham, Casino and Grafton. In Australia it has the potential to spread in coastal regions of NSW and Queensland.

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

Identification

• Tropical soda apple is an upright much-branching perennial shrub growing to 2m in height. It has broad-based, straight, cream-coloured prickles to 12mm long scattered on most plant parts.
• Leaves are mostly 10-20cm long and 6-15cm 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, with five petals 2-4mm long. They occur in clusters of three to six, off a short stem.
• Mature fruit are yellow and golf-ball size (20-30mm in diameter). When immature they are pale green with dark green veins, like immature water melons.

Spread

Tropical soda apple reproduces by seed and can regenerate from root material. In NSW, cattle movement is likely to be the major vector of spread. The occurrence of the weed near sale yards (Casino) in NSW supports this theory. However, seed can also be spread by feral animals and birds that feed on the fruit, and via water and contaminated produce, soil and equipment. It is strongly recommended that stock from affected areas are held in a weed-free area for 48 hours before being transported to other properties or to sale. Operators of cattle handling facilities are encouraged to be on the lookout for Tropical soda apple seedlings at their site.

Control

• Individual plants can be manually removed, but care must be taken to remove all the root material, as plants will regrow from root fragments.
• Fruit should be collected and disposed of appropriately (deep burial or burnt).
• There are herbicides approved for Tropical soda apple control.
• Prevent stock from grazing and moving through infested areas and manage feral animals where appropriate.
• Landowners should check cattle camps, yards and feral animal haunts for new infestations.
• Particular care should be taken to remove plants in flood-prone areas.

Distribution map as at May 2017

Predictive mapping supplied by Queensland Biosecurity