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The weed

Bugweed (Solanum mauritianum Scoop.) is a fast-growing, soft-woody, evergreen shrub to small tree of South American origin. It has​ a dense covering of soft, white hairs on the stems, flower stalks and underside of the leaves. The leaves are large and soft, especially when growing in the shade; they can reach a length of 250 mm, the upper surface being dull green and velvety, while the lower surface is white and felty. Purple to lilac flowers are borne in terminal clusters and give rise to round berries, approximately 10 mm diameter, which change from green to yellow when ripening. The berries, which are popular amongst frugivorous birds, contain an abundance of seeds. These are dispersed in the droppings of the birds, resulting in large numbers of seedlings germinating in disturbed habitats kilometres from the mother plant. Bugweed invades forest margins, plantations, roadsides, urban spaces, but also sparsely forested ravines in protected areas. Besides shading out indigenous vegetation, bugweed causes great economic losses in plantations, its hairs act as skin and respiratory irritants, and the unripe berries are toxic.

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Control

In terms of the Alien and Invasive Species Regulations (AIS), National Environmental Management: Biodiversity Act (Act No 10 of 2004), bugweed has been declared a category 1b species, which necessitates its control, or removal and destruction if possible. No trade or planting is allowed. Small plants can be uprooted manually, and large plants may be ringbarked at ground level, or cut down close to the ground and the stumps treated with recommended herbicides. The seeds of inaccessible plants will, however, always cause re-invasion of cleared areas, and biocontrol is therefore deemed the most sustainable control option. The natural enemies of Solanum species are notorious for their lack of host-specificity, and decades of research (initially at ARC-PPRI and later at University of KwaZulu-Natal) into effective, host-specific biocontrol agents have culminated in the release of only two insect agents: a leaf-feeding lacebug, Gargaphia decoris, and a flower-bud feeding snoutbeetle, Anthonomus santacruzi.  

More information

​Contact: Dr Terry Olckers, University of KZN, E-mail: olckerst@ukzn.ac.za​.