By Bob and Ena Mcintyre Garden Route Branch s1

Weeds in our Area (Part Seven) By Bob and Ena McIntyre – Garden Route Branch.

Australian Acacia Species Continued.

In the previous article we looked at Category One Australian Acacia species that occur in our area, today we examine Category Two.

Some of the more prolific Category Two Acacia invaders in our area are Acacia mearnsii (Black Wattle) and A. melanoxylon (Blackwood). The classification stems from their economic value in controlled environments. In uncontrolled environments they are particularly invasive.

Black wattle was introduced from Tasmania to the Camperdown area of Natal duirng the 19 th century. It was planted commercially for the production of tannic acid, used in the leather industry. The wood is currently widely harvested and exported as pulp to Japan for use in the production of high quality paper.

In our natural areas it has however become a serious problem, as have all other invaders. The distribution map of A. mearnsii (Black wattle) indicates the extent of invasion in South Africa. In spring when the trees produce their yellow to cream flowers, the extent of the infestation of watercourses and wooded areas become very obvious. Black wattle coppices readily and requires herbicide application when felled (any of the four methods of herbicide use discussed in Part Six can be used). Follow-up operations are imperative as a mature tree produces vast quantities of seed that can remain viable for up to 50 years or longer.

Australian Blackwood was introduced for timber production and is widely used in the furniture manufacturing industry. Blackwood coppices readily and also regenerates from vigorous root suckers. Any attempts to eliminate this species must include the use of an appropriate herbicide. This species produces prolific quantities of long-lasting seed.

A quick and effective method to reduce the seed bank is the use of fire. This practice accelerates germination but should only be used when weather conditions permit and there is no possibility of unintentionally triggering a runaway fire (contact your local authority to ascertain any local burning restrictions). Follow-up weeding or applying herbicide to the seedlings is critical. Only consider spraying herbicide when it can be done with little or no impact on any indigenous plant re-growth. If burning is possible, most of the biomass should be removed to reduce the heat intensity in order to ensure that indigenous seed banks are not destroyed as well.

During 2003 the authorities were considering legislation requiring landowners intending to sell to clear the land in question of weeds and invader plants. Whatever the outcome, now is always the best time to implement a clearing plan in order to avoid pitfalls later.