Grassroots September 2016, Vol. 16, No. 3 | Page 39
Congress
Workshop: Invasive Species
Elbé Hugo
T
ARC (Grain Crops Institute), Potchefstroom
[email protected]
he 51st Annual Congress of the Grassland
Society of Southern Africa was recently
held at The Wilderness Hotel in Wilderness
and was followed by an Invasive Species
Workshop which was held on the last day of the
congress. The Workshop was organised partly by
the Society’s organising committee and partly by
Dr PJ Pieterse. Fifty one delegates from across
environmental, pasture, forest and agricultural
fields involved in invasive species attended the
Workshop. There were nine guest speakers
covering veld management with regard to invasive
plants in rangeland and its control strategies. Dr
Sue Milton, a veteran in her field, gave an
informative overview with regard to the differences
between invaders and survivors. Typical invader
species lack natural enemies, produce abundant
seed that can be dispersed over long distances and
usually be long-lived for several years. These
species also have certain characteristics that can
protect or defend them against herbivores and that
can provide multiple recovery tactics. Survivor
species on the other hand are species that remain
after poor or neglected field management. These
species are usually unpalatable or poisonous,
proliferate seed poorly and have a week seedbed
that is not retained in soil for long periods. Prof
Nico Smit reported on bush encroachment being
one of the biggest problems in the savannah biome.
He suggested that the cost effectiveness of
chemical control of invasive bush species should be
carefully looked at and managed since it depends
on the rate of re-establishment of species and the
necessary follow-up control which will result in
secondary costs. He warned that landowners should
rather do nothing, than do the wrong thing since
disturbance may only be a trigger to enhance bush
encroachment. He emphasised that the management
of bush encroachment is a long-term control
strategy and where possible should be seen and be
approached as a resource rather than a problem.
Dr Pieter Winter from the South African
National Biodiversity Institute (SANBI) gave an
informative presentation on why it is necessary to
identify invasive species correctly. There has to be
a knowledge base since invasive biology is
dynamic and change over time. The South African
National Biodiversity Institute contains various
herbarium collections which require constant
examination, therefore the expertise of taxonomists
should not be overlooked. Dr Seb Rahlao also from
Grassroots
SANBI gave an overview of the National Status
Report on the biological status of invasive plant
species. The Alien and Invasive Species
Regulations (2014) and the respective lists of
invasive species (559 spp.) are available on the
website, www.invasives.org.za. These invasive
species are categorised according to the National
Environmental Management: Biodiversity Act
(NEMBA) into four groups (i.e. 1a, 1b, 2 and 3)
according to their invasive status. The ideal is to
update these lists every six months, however the
feasibility is questionable. The National Status
Report gives information on the distribution, rate of
spread and risk assessments involved of invasive
species.
Dr Graham Harding elucidated the role of
herbicides in invasive alien plant management and
stated that chemical control is an essential tool in
management strategies. He accentuated the
importance of understanding the application and
use of the different products registered to be used
in controlling various invasive species. It is not
realistic to ban chemical control from management
strategies, rather use less herbicides, but use it
correctly, at the right time and adhere to label
recommendations of each product.
Dr Helmuth Zimmerman ended the workshop
with the exceptional successes with the biological
control of invasive Cacti in the north-western
grasslands. He gave an overview of the work that
has been done to control Opuntia engelmannii with
four cochineal species (sap-sucking insects). It was
a journey with trial and error, but at the end all the
research and hard work paid-off. Biological control
cannot eradicate invasive species completely, but
the main objective with biological control is to get
a balance between the host and the predator.
Dr Zimmermann also informed the workshop
that new invaders are always on the horizon and
gave an update on invaders such as Opuntaelata
Harissiatortuposa, Thephrocactus articulates,
Cylindropuntia spinosior and C. pallida.
Other speakers included Mr. Justin du Toit from
Department of Agriculture, Forestry and Fisheries
who explored invasive plant management strategies
in
grassland
especially
where
slangbos
[Seriphiumplumosum (syn. Stoebe vulgaris)] and
katbos (Asparagus laricinus) were predominant. Mr
September 2016
Vol 16 No. 3