Euston-Brown, D., Rathogwa, N & Richardson ... - DWA Home Page

Species Common
name
Solanum seaforthianum
Potato
creeper
Weed status in
South Africa
(Nel et al. 2004)
Major invader
(widespread–
common)
Growth form Habitat preference Priority Notes
Slender,
herbaceous,
softly woody
climber
Tagetes minuta kakiebos Erect
herbaceous
annual to 2 m
Tithonia diversifolia
Xanthium
spinosum
Xanthium strumarium
Mexican
sunflower
Spiny
cockelbur
Large
cocklebur
Emerging
invader
(Moderate–
moderate)
Erect annual or
perennial up to
3.5 m
- Spiny annual
up to 1.2 m
Savanna, woodland,
riparian habitat
Widespread,
disturbed places,
cultivated lands,
grassland and
savanna
Savanna, grassland,
roadsides, open river
banks
Open river banks,
cultivated lands, old
lands
Major invader Annual to 1.2 m Cultivated lands, old
lands, roadsides,
open river banks
1 Poisonous fruits, leaves and
stems
2 Extract from leaves used
in perfume industry; Drives
away nematodes in soil;
Odour downgrades maize.
2 High visual impact
1 Herbicide registration.
Poisonous seedlings, seeds
and burs.
1 Herbicide registration.
Poisonous seedlings, seeds
and burs.
It is essential that managers and clearing teams learn how to identify the invasive plants listed in
Table 2. It was noted that at many sites where WfW have been clearing that some of the less obvious
herbaceous weeds (e.g. Ageratum conyzoides, Solanum seaforthianum, Xanthium spp etc) were left
untreated. Identification of these weeds in savanna systems is not simple because there are also a large
diversity of indigenous herbs, shrubs and trees some of which also display “weedy” characteristics. An
alien clearing operation needs to plan to deal with these other invasive plants, especially in follow up
situations when they tend to establish readily.
4.2.5 Description and assessment of the invasion problem
The invasion by these two species into the area under consideration is still fairly recent. Thus there are
many suitable habitats, especially in Mpumalanga and Limpopo provinces, that are still relatively free
of dense infestations. Chromolaena is virtually absent from lower rainfall areas, but there are sporadic
outbreaks in drier parts after rainfall events, but these tend to die back and disappear in drought
periods. Lantana appears to be more tolerant of droughts than chromolaena and can persist through
drought periods.
Although there are obvious differences between the two species, the process of establishment and
spreading into new areas seems to be facilitated by veld degradation through a combination of factors
such as overgrazing by cattle, disruption of frequent fires, and bush encroachment that reduces grass
cover and fire behaviour. Thus, if the factors leading to veld degradation are not remedied, the system
remains highly susceptible to re-invasion by the same species. It is possible for the situation to become
even worse because the disturbance created by clearing usually stimulates the invasion of a range of
other herbaceous weeds. If follow up operations are not done in good time, or worse if they are not
done at all, then it is possible to end up with a wider diversity of alien species at higher density. This
situation is far more difficult to manage than the initial situation with one alien species dominating.
Development of a clearing protocol based on ecological criteria for Mesic Savannas and Sweet Grassveld for the Working for Water Programme
21