Controlling an invasive species demands a well-planned management, which includes the determination of the invaded area, identifying the causes of invasion, assessing the impacts, defining the intervention priorities, selecting the adequate control methodologies and their application. Afterwards it is fundamental to monitor the efficiency of the methodologies and recuperation of the intervened area as to perform, whenever necessary, the follow-up control.
The control methodologies used for Acacia dealbata include:
Physical control
Hand pulling: preferential methodology for seedlings and small plants. When in more compacted substrates, pulling must be made during the rainy season as to facilitate the removal of the root system. It should be guaranteed that no roots of large dimensions are left in the ground.
Cutting with brushcutter: preferential methodology for plants resulting from the germination that are still very small. It should just be applied on warm days as long as the security conditions are respected.
Ring-barking: preferential methodology for adult plants with a smooth, unwounded bark. Make a continuous ring incision around the trunk, at the height most comfortable for the operator, and remove all the bark and vascular cambium until the ground surface, if possible, until the root. It should be applied only when the vascular cambium is active, which may vary from place to place; the best seasons for this technique coincide with warm temperatures and some humidity.
Physical + chemical control
Cut stump method: apply to adult plants. Cut the trunk as close to the ground as possible and immediately (in the following seconds) apply herbicide (active substance: glyphosate) to the cut stump. If shoots should latter on appear, these should be immediately eliminated through cutting, pulling or foliar application of herbicide (active substance: glyphosate); up to 25 to 50 cm high. Shoots of larger dimensions (from 2-3 cm diameter) may be ring-barked or else should be repeated the initial methodology (cut stump method).
Chemical control
Foliar application of herbicide: over recent sprouts (25-50 cm tall) or when high germination rates occur. Spray with herbicide (active substance: glyphosate) limiting as much as possible its application to the target species.
Stem injection: applied to adult plants. Apply the herbicide directly on the vascular system of the plant with one of the following techniques:
1) Cut + injection: make several cuts (with an axe or saw), at the height most convenient to the operator, in an angle of 45º until the sapwood, and immediately inject (in the following seconds) the herbicide in each incision with a squirt bottle. Apply around 1ml (0,5 to 2ml, according to the size of the cut) of herbicide in each incision.
The several cuts should be made at the same height on the trunk as to nearly touch, leaving around 2-4 cm of uncut bark between them. For smaller plants, only 2 or 3 cuts are necessary and they shouldn’t be deep (to prevent the plant breaking).
2) Drilling + injection: drill holes (with a drill) around 10 cm deep around the trunk and in each hole immediately inject (in the following seconds) the herbicide (1 ml) with a squirt bottle.
The holes should be made at a height most comfortable to the operator, in a 45º angle (to avoid the herbicide’s runoff) and in intervals of 5-10 cm between them. The number of holes to make depends on the plant’s diameter.
Biological control
The biological control agent Melanterius maculatus Lea (Coleoptera: Curcullonidae) was released in South Africa to destroy the seeds; its establishment has been confirmed, although the damage caused to the invasive species hasn’t been confirmed.
Although initial steps for the testing procedure are being made to verify its security relative to native species, this agent has not yet been tested in Portugal, so its use has not yet constituted an alternative in our country.
Prescribed fire
It may be strategically used to favour germination of the seed bank, e.g., after the control of adult individuals (with the adequate management of the resulting biomass) and the subsequent elimination of seedlings. This method provides an advantageous reduction of the seed bank, both by destroying part of the seeds or by stimulating the germination of the remainders.
Visit the webpage How to Control for additional and more detailed information about the correct application of these methodologies.
