African boxthorn is a woody dense shrub with sharp spines forming thickets that displace native vegetation, affect local fauna, threaten agriculture and may harm people, animals and pets.
Description
African boxthorn is a long-lived upright dense shrub growing up to 5 m high and 3 m across with thorny spines along rigid branches and spine-tipped stems that can form impenetrable thickets.
The plant has an extensive, deep central taproot and branched root system that endures periods of drought, fire and stress. The taproot will sucker and produce new growth if broken.
Leaves are oval-shaped light green and fleshy 10 to 40mm long. They occur in clusters along branchlets. Leaves often fall off over winter or when stressed. Plants may appear dead, with new leaves shooting in spring or after rain.
Flowering and fruiting occurs mostly over spring and summer. Tubular at the base, flowers are pale lilac or white in colour with darker purple inner markings. Flowers have 5 petals bent backwards with protruding stamens.
Large fruiting plants can produce thousands of round orange-red berries partially encased by a green calyx (cup of leaves). Each berry contains 20 to 70 light brown seeds 2.5 mm long. Although seeds are considered to not live long in the soil, they can germinate any time of the year when conditions are favourable.
Similar species
Native Australian boxthorn (Lycium australe) is similar to African boxthorn but has small, relatively narrow, thick and fleshy, greyish-green leaves. Flowers are creamy white to mauve, stamens do not protrude past the petals. Berries are smaller and oval-shaped not round and contain only 5 to 20 seeds.
Impacts
Thickets of African boxthorn outcompete native plant species affecting native fauna, alter flow patterns in watercourses, block access along tracks, and reduce the value of pastoral land. African boxthorn can cause harm to livestock, animals and people with all parts of African boxthorn being poisonous. Leaves are considered toxic to poultry.
Sharp spines limit grazing and provide shelter for pest species such as rats, rabbits and foxes. The fruit of African boxthorn can host fruit fly, affecting agriculture and suburban food production.
In some situations African boxthorn plants are providing valuable habitat for some of our threatened bird species like the coastal white fairy wren, where their natural habitat has been removed or degraded. If no shrubs other than African boxthorn are present, then consider establishing replacement planting prior to staged removal of the weed.
Distribution
African boxthorn originates from southern Africa and was originally planted in Australia as a hedging plant and windbreak. In the Green Adelaide region, African boxthorn can be found along roadsides and waterways, on idle farming lands, in reserves and native vegetation and is abundant along coastal areas.
African boxthorn requires an annual rainfall of 200 mm and tolerates poor soils, variable climates, exposed sites and salty conditions. It colonises degraded or naturally disturbed landscapes with new infestations commonly found under trees, along fences and under powerlines germinating from seed excreted by perching birds.
Digestion of seed by birds and other animals is the most common method of spread but movement of contaminated produce, machinery, vehicles, and soil, and dumped garden waste also spreads seed. Roots have the ability to produce new growth from broken segments and the branched root system can produce sucker shoots.
Management
African boxthorn (Lycium ferocissimum) is a declared weed under the Landscape South Australia Act 2019 and a Weed of National Significance.
To prevent the spread in the Green Adelaide region, the sale of this plant or contaminated goods is prohibited and the movement of either on a public road is restricted.
Land owners must take reasonable steps to control plants on their property.
We encourage control of plants where there is a risk to human health, agriculture, and biodiversity. Undertaking weed control needs to be done carefully to prevent damage to native vegetation.
Control methods
Hygiene
Prevention of seed set will minimise infestation and is best achieved by removing young plants. When controlling African boxthorn, care must be taken to remove all root stock and collect all plant material to burn on site with consideration of local fire regulations.
Mechanical
Ideal for paddocks and degraded sites, small infestations and single plants can be removed manually using machinery any time when plants are not in seed. Plants are easier to remove if the ground is moist.
Chemical
Foliar spot spraying in non-crop and pasture areas is effective when plants are actively growing usually late winter/early spring and prior to bud burst. Ensure plants are not moisture-stressed and complete coverage of plant is achieved for maximum chemical uptake.
Basal bark (spraying of trunk) treatment in non-crop and pasture areas is suitable on stems up to 5 cm diameter. Larger stems can be cut and swabbed anytime.
African boxthorn will react to the herbicide by losing its leaves and appear dead but may regenerate with new shoots and leaf growth. Repeat chemical application until the plant dies.
For advice on chemical options please refer to Controlling declared weeds in SA from PIRSA.
Observations of weeds can be entered into iNaturalist, an app which can assist with identification.