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July 2014

This month, we look at the more problematic Eucalyptus genus, better known as Gums. The genus Eucalyptus, with about 800 species, belongs to the myrtle family and is almost entirely native to Australia. They are best known for their commercial use as timber trees and windbreaks. They are also cultivated for ornament, shade, firewood and honey production. Eucalyptus leaves contain highly volatile and flammable oils, which together with the accumulation of dense leaf litter, can result in very fierce fires, endangering properties, humans and the native fauna and flora. It is likely that most Eucalypts are also allelopathic. (having the potential to suppress under-storey plants through chemical inhibitors that leach into the soil)

Most invasion occurs along water courses, but also on forest margins, in gaps within native forest and plantations, as well as into Fynbos and grassland. Eucalypts are well known for their ability to use large volumes of water and this usage increases with abundant availability of water - such as along watercourses.

Lesley Henderson’s SANBI Weed ResearchProgramme lists 2 species as problematic in our area, namely the Red River Gum (Eucalyptus camaldulensis) and the Saligna or Rose Gum. (Eucalyptus grandis)
The Red River Gum is not used for commercial afforestation, but is widely cultivated in SA in farm woodlots and shelter belts under cool, dry conditions. The Saligna Gum is grown commercially and extensively for timber in the NE provinces of SA.

  • Red River Gum: Originates from Australia where it has widespread occurrence in every state except Tasmania; it is large tree with an open pale-green crown of intermediate spread; bark is attractively mottled, greyish-white; mature leaves arise alternately on different sides of branchlets and are 12-22 cm. in length, stalked and pendulous, lance-shaped and obliquely veined along the midrib; flowers are produced in stalked clusters in leaf axils throughout summer and yield abundant nectar and pollen; fruit is 7-8 mm long, hemispherical in shape with a domed rim; very frost hardy.

  • Saligna Gum: Originates from the warm, humid coastal regions of Queensland and New South Wales in Australia. A tall tree, with a clean bole; bark peels in long thin strips, exposing a smooth, powdery grey, white or greenish surface,with some rough flaky bark at the base up to 4 m. Leaves: Are long and narrow, lance-shaped and have numerous fine veins. Flowers: Are found in clusters in the axils of the upper leaves. Fruit: Is short-stalked and pear-shaped. This species invades forest gaps and watercourses.

 

Control: Cut stump, application of Hatchet or Chopper on cambium (inner bark) area of low cut stump. Use 10% solution in water on Red River Gum and 5% solution on Saligna Gum.  Any stump re-growth can be treated (when knee height), with a foliar application of Brush Off or Nicanor at strength of 125gm. per 100L. of water. Use should be made of a wetter to prevent herbicide run-off.
References:

  • Our Green Heritage: The SA Book of Trees 1973
  • Sapia News – Vol. 12
  • Mike Martyn - Silvex

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