Download Article 63 Acacia saligna - Botanical Society of South Africa

Weeds in our Area (Part Sixty Three)
By Bob and Ena McIntyre, Botanical Society of S.A. – Garden Route Branch
The South African connection with the Australian Acacia species has a long history. This time we look at Port
Jackson Willow (Acacia saligna). The Port Jackson Willow is native to south-western Australia and was
imported into South Africa in the mid 1800’s. Baron von Ludwig refers to a batch of Australian Acacias
imported in 1835 but does not name any individual species. It is however recorded that the Colonial
Secretary, the Hon John Montagu, had imported Port Jackson by 1847. These, together with other Australian
plants were used to bind the drift sands along the first road to be constructed across the Cape Flats - from
Cape Town to Bellville and beyond. The stabilisation effort was very successful and still today, the area is
dominated by Port Jackson Willow (Acacia saligna) and Rooikrans (A. Cyclops) wherever there is vacant
land. The spread of Port Jackson (A. saligna) is predominant in coastal areas with a mean annual rainfall
exceeding 250mm. Although mainly confined to the region between the Olifants River in the West and the
Kei River in the Eastern Cape, infestations are found as far as Kosi Bay and the Gariep (Orange) River. The
plants are found in mountain and Lowland Fynbos, forest areas, grasslands and Succulent Karoo.
Identification: As with all Australian Acacias
Port Jackson is an unarmed (no thorns) shrub
or tree 3-10 m high with a willow like
appearance. The introduction of a rust
fungus as a bio-control agent has resulted in
badly deformed stems, characterised by
large, brown, irregularly shaped galls. The
leaves are phyllodes (leaf-like petiole with no
blade) blue-green turning green up to
200mm long and 10-50mm wide mainly
pendulous, with a single mid-vein. They are
broader and somewhat wavy on young
plants. The flowers are a bright yellow with
globular flower-heads from August to
November. The seed pods are brown with hardened whitish margins.
Control: Young Port Jackson Willow (up to 3m), can be sprayed with a glyphosate (RoundUp) at a 3% mix
with water. Felled plants need a cut stump treatment with an effective herbicide to prevent coppicing.
Freshly coppiced plants can be treated as for young plants (see above). A bio-control agent Uromycladium
tepperianum that produces galls on any young tissue (see photo) was released in 1987. The effect of this
agent is evident on most Port Jackson plants and is considered to be successful. A seed feeder, Melanterius
compactus released in 2001 has had moderate impact.
Substitutes: Many of our indigenous smaller trees and/or large shrubs will fit the bill. Buddleja saligna
(False olive), Calpurnia aurea (Natal Laburnum), Rhus crenata, Allophylus decipiens (False currant), Brachylaena
discolour (Coast silver oak), are a few indigenous alternatives.
Illustrations: “AFRICA invaded”: Published by The Global Invasive Species Program 2004
BotSoc Forthcoming Events
Knysna: Sunday, 11 June, 10.00 am: Collection and planting of fynbos plants for Pledge Nature Reserve.
Bring forks, plastic bags and lunch. Meet in the parking lot at Pledge at 10h00. To participate please contact
Chris or Ariane below.
Plettenberg Bay: Saturday, 17 June - Hack at Lookout Park. Bitou municipality are on course to declare
this a Nature Reserve. To participate please contact Jean or Maaike below.
BotSoc Contacts in your area: George/Wilderness: McIntyre’s 044 877 1360
Knysna: Chris Gow 044 387 1978, Ariane Rohloff 044 382 7993
Mossel Bay: Lucretia van der Walt 044 691 3230
Plettenberg Bay (Bitou Twig): Jean Sparg 044 533 2625, Maaike Murphy 044 531 6857
Stilbaai: Janet Naude 028 754 1106