Alien Invasive Plants in South Africa Management and Challenges

Alien Invasive Plants in South Africa:
Management and Challenges
Carl Reinhardt
University of Pretoria
Republic of South Africa
E-mail: dr.charlie.reinhardt@gmail.com

Africa in relation to Europe

Contrast between small and commercial scale farming in Africa is large

Maize and cassava are staple crops,
here with peanuts as intercrop to
contribute nitrogen.
Subsistence farming is a way of life
for the majority of Africans living in
rural areas.

Many projects in Africa fail due to lack of appropriate knowledge ‒
resulting in disturbance of ecosystems
Failed biodiesel project in Mozambique
– Jatropha curcas on 10,000 ha

South Africa is for the greater part a water-stressed country.
Most regions receive

Disturbance of natural habitats:
• Fire is a natural factor which is
exploited by humans for vegetation
management
• Mechanical clearing of
vegetation is most destructive ‒
creates space for alien invasive
plants

Indigenous species can
“densify” and dominate due
to disturbance of vegetation –
in this case due to overgrazing
Stoebe spp
Asparagus spp

South America origin: Opuntia ficus-indica
Biocontrol with insect,
Dactylopius opuntiae

Examples of alien species deliberately planted for shelter,
fuel (firewood), building material
Populus canescens
Eucalyptus spp

European origin: Populus canescens
Typically invades wet habitats

Campuloclinium macrocephalum ‒
imported for horticulture, but devastating
to grassland
Origin: South America

Conyza spp on fallow crop fields

Solanum elaeagnifolium in Roundup Ready® maize

Alien Invasive Plants in the Kruger National Park, South Africa
Alien invasive plants represent a
serious threat to natural biodiversity in
this conservation area of 20,000 km 2 .
More than 350 alien plants occur
in KNP, of which about 30 are
highly invasive.

Parthenium hysterophorus (Asteraceae) ‒ annual/biannual; herbaceous
A recent invader whose
spread is promoted by
humans and natural forces

Parthenium preferentially invades
disturbed areas.

Field trial: Interference potential of P. hysterophorus with indigenous
grass species in the KNP

Parthenium plants on 18 Jan 2004

10 Feb 2004
One meter
height
increase in
3 weeks!

Lettuce grown together with Parthenium plants in hydroponic solution
Control 2 Parthenium 4 Parthenium

Parthenin content in various parts of P. hysterophorus
Parthenin
mg/g
16
14
12
10
8
6
4
2
0
14.5
4.5
3.7
1.1
0.17 0.1
root stem leaf flower fruit pollen

-----------
---- dip ----
-----------
-----------
homogenisate
-----------
Parthenin [mg/g]
Parthenin in TBME leaf-dips, and in leaf-homogenates after dipping
14
12
10
8
6
4
2
0
In TBME (organic solvent)
13.4
11.2
12.0
1.4
In leaves post-TBME
1.2 1.0
Old Intermediate Young
Old Intermediate Young
Leaves of different age
Leaves of different age
•REINHARDT, C.F., VAN DER LAAN, M., BELZ, R.G., HURLE, K. & FOXCROFT, L., 2006. Production dynamics of the
allelochemical parthenin in leaves of Parthenium hysterophorus L. J. Plant Diseases and Protection 20, 427-433.
•BELZ, R.G., REINHARDT, C.F., intermediate
FOXCROFT L.C. & HURLE, K., 2007. Residue allelopathy intermediate
Parthenium hysterophorus L. –
Does parthenin play a leading role? Crop Protection 26, 237-245.
•VAN DER LAAN, M., REINHARDT, C.F., BELZ, R.G., TRUTER, W.F., FOXCROFT, L.C. & HURLE, K., 2008. Interference
potential of the perennial grasses Eragrostis curvula, Panicum maximum and Digitaria eriantha with Parthenium
hysterophorus. Tropical Grasslands 42, 88-95.
old leaf leaf juvenile
leaf
old leaf leaf juvenile
leaf

Management of alien invasive plant species
• Maintaining natural biodiversity is key ‒
disturbance/degradation directly or indirectly by humans is a
major destroyer of diversity.
• Chemical control (herbicides) has limitations in natural
ecosystems: non-selectivity; environmental contamination.
• Biocontrol using natural enemies are highly selective and
takes a long time to be effective.

Before biocontrol
Aquatic alien invader Pistia
stratiotes in Sunset Dam, KNP
Insect biocontrol agent
After biocontrol

Special thanks to THE TEAM