Alien Vegetation in our region: Solanum mauritanium
The Layman’s Guide to Invasive Alien Vegetation in our region
Southern Cape Weeds Forum
Ena & Bob McIntyre – Garden Route Branch.
Solanum mauritanium (Bugweed)
Bugweed (Solanum mauritanium) – origin South America – is a category 1b weed thought to have been introduced as a garden plant. S. mauritanium was first reported as showing invasive tendencies in KZN in the 1860’s. Since, it has spread all along the coast to the Cape.
Apart from the unripe fruits being poisonous, the fruit acts as a host to the fruit fly with obvious negative implications for the deciduous fruit industry. Birds are attracted to the fruit and are unaffected by the poison. Where bugweed occurs in young plantations, fruit eating birds perch on young pine trees, breaking the growing tips causing deformed growth. It has also been noted that where the plants occur, birds appear to have developed a preference for the bugweed seed over seeds of indigenous trees and shrubs. Consequently birds are acting as seed dispersers for the weed with negative consequences for biodiversity in general and local forestry.
Identification: Solanum mauritanium is a fast-growing shrub or small scraggly tree with large dull grey-green leaves, velvety above and white felty undersides making the plant easily identifiable. All parts except older stems are also covered with whitish-felty hairs. Clusters of purple flowers occur throughout the year. The fruits are born in compact terminal clusters of berries of 10mm across, turning yellow when ripe. Common along degraded road-sides, plantation logging tracks and water-courses Bugweed is often confused with the indigenous Solanum giganteum (Healing-leaf tree). Very similar in appearance, S.giganteum is readily identified when not in fruit by short straight spines on the stems and branches and when in fruit – bright red ripe fruits as opposed to S.mauritanium’s yellow fruits.
Control: Foliar herbicide application is impractical due the rapid growth, as the foliage is generally out of reach. Felling the plants and treating the stump with the herbicide Timbrel is very effective. Alternatively frill the stump and treat the frill with Timbrel. Any clearing must have a follow up program to address seed germination that will occur. On the biological control front two leaf-feeding beetles released in 1992 are showing very good results. Mechanical clearing dislodges clouds of the fine hairs on stems and foliage which is reported to contain toxins blamed for respiratory problems in workers exposed to the dust.
Line drawing with acknowledgement to “ALIEN WEEDS AND INVASIVE PLANTS” by Lesley Henderson. Copyright © 2001 Agricultural Research Council.
Contributor: Lorna Watt (WESSA)