Weeds in our Area (Part One Hundred and Twelve)
By Bob and Ena McIntyre – Garden Route
BIOLOGICAL CONTROL CONTINUED
Sesbania punicea (Red Sesbania)
Over fifty species of Sesbania are found world wide. A perennial shrub native to South America,
Red Sesbania (Sesbania punicea), is a problem in South Africa and many other countries. Like so
many others, in all likelihood introduced into South Africa as an ornamental garden plant, it has
since the 1960’s spread alarmingly throughout all of South Africa except for the dry north-western
region. Already in 1979 it was declared a noxious weed and is now classified as a Category One
Invasive species.
Impacts: Red Sesbania establishes itself in mono-specific stands impacting on indigenous plant
diversity. The main impact however, is its toxicity. All parts of the plant have a low level of toxicity
while the seeds are particularly lethal to birds and also affect sheep. As few as 6 seeds are known
to kill a chicken and pigeons are common casualties.
Three biological control agents have been released. In the 1970’s a
flower-bud feeder Trichapion lativentre was released. Two other
agents, a stem borer Neodiplogrammus quadrivittatus and a seed
feeder Rhyssomatus marginatus were released in 1984. The
combined effect of the three is said to now control the spread of
this weed. Despite this, pockets of Sesbania do appear in our area.
Sesbania is found mainly in wet areas but also establishes itself
readily in disturbed ground. Once established, it can transform an
area into a dense mono-specific stand.
Identification: S. punicea is a deciduous small tree or shrub up to
4m with many slender branches, giving it a rather delicate
appearance. The leaves
are pinnate, 100-200mm
long. Leaflets are dark
green,
oblong
with
pointed tips. Showy dense sprays of orange-red peashaped flowers appear between September and March.
The seeds are contained in brown pods with four
longitudinal wings. The distinctive four-winged pods (see
photo) are 60-80mm long x 10mm wide and the tip is
sharply pointed. The plants are common along the Road to Knysna and isolated patches have been
seen in Hoekwil.
Control: As manual control, strip barking is effective. However follow-up is necessary to ensure
that the plant does not put out shoots from the root ball. Should this happen, remove any new
shoots. A word of warning - slashing without stump treatment induces vigorous re-growth. Many
herbicides are registered for cut stump and foliar applications. Seedlings and re-growth may be
sprayed with a foliar glyphosate spray such as Round-up or Mamba. Garlon or one of the other
triclopyr herbicides may also be used. Cut stumps should be treated with Chopper or a
Garlon/diesel mix.
Substitute: Several stunning local shrubs such as Cape Indigo (Indigofera frutescence) and the
dwarf Coral Tree (Erythrina humeana) will thrive in local conditions and bring colour and texture to
any garden.
References: Alien Weeds and Invasive Plants by Lesley Henderson, Copyright © 2001 Agricultural
Research Council. Problem Plants of South Africa by Clive Bromilow 2001.
http://www.wikipedia.org and http://www.arc.agric.za.