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13 - 19 March 2018
Invasive plant species are not water-wise Much has been written in the last few months regarding water-wise gardens to save water. But the invasion of other plant species is destroying the environment of the Overberg. They are also a fire hazard and use much more water than indigenous plants, writes local botanical experts, MIKE AUSTIN and BRUCE BAYER.
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he most common invasive weeds in the Overberg are Port Jackson, myrtle, rooikrans, pine and, to some extent, eucalyptus. These are all listed as category 1a or 1b in this area and have to be removed from public and private land, in terms of the National Environmental Management: Biodiversity Act. It is therefore illegal to have these and other listed weeds on your property. The methods of removing them are also specified in the regulations. They are all Australian imports and are a real problem in the Overberg, as a 2-year old tree can produce thousands of seeds which spread onto adjoining plots. Port Jackson (Acacia saligna) Port Jackson is by far the most wide-spread invader. This is an evergreen tree and can grow up to between 3 and 7 metres. The leaves are blue-green through to bright green. It has bright yellow globe-shaped flowers from August to November. It develops brown pods with
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hardened whitish margins. Extensive invasion has occurred in the last decade within the Overberg built up areas and its surrounds. This is a major fire hazard, with a tentimes more intense burn than fynbos, which the Port Jackson is replacing. Removal methods for Port Jackson The removal of young seedlings is the easiest and cheapest way, leaving nothing to cart away. They must be pulled out or cut off just below ground level. The root tends to
go straight down when young. If the base of the plant is not removed, it branches profusely. Within a year it will regrow much quicker because the root system is left intact. With the profuse branching, the infestation is five or six times worse, because of the multiple branching from the base. These branched stems are much more difficult to remove and costs of removal will therefore skyrocket. Bigger specimens have to be cut off close to the ground and painted, and not sprayed with herbicide such as Garlon
or Confront immediately after cutting. The spraying of chemicals onto the stump will cause damage to surrounding plants and uses as much as 10 times the amount of expensive chemicals, which then severely pollutes the environment. Australian myrtle (Leptospernum laevigatum) This is the second most invasive species in the Overberg. This is a large denselybranched, untidy, spreading small tree up to 8 metres high. It has dull grey-greenish leathery leaves and has solitary
white flowers from August to October with green fruit which turns yellow and then grey. The removal of this species is more complicated because of difficult access to the base to chop it down. It also roots from branches touching the ground. All stems need to be removed as well as any exposed roots. Large stems should be painted with herbicide. Follow-up treatment within a year is very important. Eucalyptus There are many invasive plants in this genus and the Spider gum, Eucalyptus conferruminata, is the most common in the Overberg. It can grow into a large tree with smooth whitish grey bark. Adult leaves are elliptical and 9 X 2.5cm in size, glossy and light green. It has yellowgreen flowers in spring and summer. The seed capsule is greyish-brown, 50 to 80mm long. It can be a real danger close to buildings as large branches often break off. The spreading of these plants is not a great problem in the Overberg and mature trees can be left in place. Young trees should be cut down and the stumps
treated with herbicide. Pines There are a number of different invasive pines such as cluster, slash and patula. They are spreading into the Fynbos and should be controlled. Mature trees can be left but young growth should be controlled. They are easy to remove: simply cut them down. The stump does not even need to be treated, as the growing points are at the ends of the branches. Other species Other declared invasive tree species e.g. bottlebrush, Brazilian pepper and Spanish broom are present in the Overberg but are not problem species at this stage. There are also grasses and herbs that are seriously problematic, such as Paterson’s curse, kikuyu and buffalo grass. If you are not sure about a particular plant, Bruce Bayer can assist you with identification and the best removal advice. If you need agricultural, ecological or building planning advice, contact Michael Austin or go to his website www.greenheart.co.za. For more information send an email to mike@greenheart.co.za