Download Article 61 Acacia Longifolia

Weeds in our Area (Part Sixty One)
By Bob and Ena McIntyre – Garden Route Branch
Acacia longifolia
Long ago, in July 2004 (Part Six) we looked at the invasive Australian Acacia species as a group. For
the sake of clarity there is much merit in examining them individually as more detailed
descriptions greatly improve one’s ability to correctly identify the different species.
One of the most common species that were introduced deliberately in 1827 for the purpose of
dune reclamation must certainly be the prolific Acacia longifolia. It was only in 1945 that the
species started revealing its invasive tendencies. These particularly persistent invaders are now
very widely spread from dense infestations in the Western Cape, eastward along the coast and all
the way up into the country as far as Mpumalanga and the Northern Province. It prefers moist
sites in fynbos, woodlands and watercourses. It quickly becomes dense thickets and can totally
transform the landscape.
Identification: Locally the species is very
common particularly in the Belvidere, Brenton
and Knysna areas where roadsides and
degraded forest areas are heavily infested. The
plants are quite easy to identify. Many sporting
mean-looking smooth spherical galls on their
stems – this is caused by an introduced wasp.
The gall starts out as green in colour, turns
brown in time and replaces the flower and leaf
buds. In stark contrast to all other invasive
Australian Acacias that have globular flower
heads, the flowers of A. longifolia are long
cylindrical flower heads (up to 50mm and
about 7 mm wide) borne in the axils of the
leaves from July to September. The flowers
are also bright yellow in colour. The leaves, as
with many Australian Acacia are phyllodes
(leaf-like petiole with no blade) bright green and up to 180mm
long with 2-5 prominent longitudinal veins.
Control: Happily A. longifolia does not coppice easily which
means that felling and burning (only when conditions are safe
and with the required permission of the local authority) is an
accepted control method. Seed germination may be controlled
with the use of a herbicide. Garlon 4 at 1% should be applied to
young actively growing saplings up to 2m in height. The release
of a gall wasp Trichilogaster acaciaelongifoliae in 1982 and a
seed feeder Melanterius ventralis in 1985 have had a significant
impact on reducing the spread of this species.
Substitutes:
Salix mucronata (Safsaf willow), Rhus lancea
(Karee), Brachylaena discolour (Coast silver oak), Acacia caffra
(Haakdoring) are some of our local indigenous shrubs and trees
that are excellent choices. For sand stabilisation, bushy shrubs such as Rhus crenata and Metalasia
muricata (White bristle bush) are suitable.
Illustrations: “ALIEN WEEDS AND INVASIVE PLANTS”: Lesley Henderson. Copyright © 2001
Agricultural Research Council.