How to remove invasive plants
As most ecologically aware gardeners already know, getting rid of invasive alien plants (IAPs) is not so easy. Their roots are invasive and their seedlings pop up all over the garden. A number of physical and chemical techniques have proven highly effective. The key to success is to persevere in your programme of eradicating IAPs. Keep removing seedlings and remember to repeat spraying with herbicides at the intervals recommended.
Many invasive plants can be removed manually or with the help of simple tools.
Seedling of many invasive plants appear in gardens all the time, courtesy of birds passing through. When seedlings appear, pull them out as soon as possible to eliminate costly tree felling at a later stage. It is easier to remove seedlings when the soil is moist.
Shrubs and small trees
Use a 'Tree Popper' to remove shrubs and smaller trees. Alternatively, cut off the top growth and then remove the stem and roots from the soil. It is vital that the root ball and any taproots are totally removed to prevent re-growth, as invasive plants often have roots capable of regeneration.
If the tree is too large for physical removal, consider ring-barking the tree. This technique involves removing a ring of bark at least 25cm wide. Peel the bark down to just below ground level, pulling outwards. Bark peeling is a particularly useful method for destroying invader acacias. Ring-barking interferes with the circulation of the tree and results in it slowly dying. If you wish to hasten the process, fell the tree to a stump that is 30cm above ground level. Then loosen the bark on the stump by hitting it with a hammer and peel the bark downwards to ground level. Any re-growth that appears must be cut off cleanly at once, to prevent nutrition from new growth reaching the roots.
There are a number of effective herbicides on the market. Always consult experts at your nearest garden centre on the application and safe use of herbicides.
Seedlings and small shrubs
Herbicides can be sprayed on plants less than 2m in height for quick results. Spray when there is no wind. This will help to avoid spray drift onto adjacent wanted plants. Some weed killers are non selective and others selective so be careful! All plants that are subjected to the spray will be destroyed – seek for professional advice on which herbicides to use.
Large shrubs and trees
Cut-stump treatment: Fell the tree, leaving a stump as flat and as close to the ground as possible, and apply a recommended herbicide.
Basal stem treatment: Paint a herbicide (mixed with diesel) onto the base of the tree trunk and any exposed roots. Paint the herbicide up to a height of 25cm above ground level. In the case of multi-stemmed trees, each individual stem should be painted. The herbicide will enter the tree's circulation and eventually kill the tree.
Foliar spraying: In the case of re-growth from stumps (otherwise known as coppicing), mix a herbicide with water and spray on the re-growth. Allow the re-growth to reach a height of 50cm before treatment. Ensure that a full cover spray is achieved. Trees with bud banks or lignotubers can be destroyed using use a herbicide after sawing off the trunk at ground level.
How do you get rid of plants that keep on resprouting? Known as regenerative plants, this group of resprouting invaders are designed by nature to survive ravaging veld fires. This ability means that they are impossible to eradicate simply by felling. Resprouting IAPs have a variety of survival techniques. Eucalyptus (Eucalyptus spp.) have woody lignotubers capable of resprouting indefinitely. Many wattles (Acacia mearnsii, A. pycnantha, A. saligna, A. melanxylon) and red sesbania (Sesbania punicea) have a section of bark situated at ground level, where the fire is coolest, which is more moist and spongier than normal bark.
This section is well supplied with undeveloped buds and acts as a 'bud bank'. The bud bank extends about 4cm below the surface of the ground to the point where the roots begin to form. Due to the size of the surviving rootstock, post-fire regeneration is extremely fast, with the plant able to seed itself again usually in as little as two years. Jeremy Croudace of the Red Hill Fynbos Restoration Project in Simonstown has developed special techniques to eliminate invader plants with regenerative roots.
Physical removal of the bud bank or lignotuber is quite easy to do on plants that are too big to pull up by hand, but not so big as to require sawing down. The best tool to use is a pair of long-handled clippers or loppers. Keep the blades closed, and push the clippers into the ground next to the main root. Use the clippers to widen a space large enough for the clippers to be opened. Then clip off the root below the bud bank.
Loosen the soil around the bud bank and pull out the plant. If there are lateral roots on the end, you know you've removed the whole bud bank. Without the bud bank the plant can't resprout, while the use of this method ensures that there is minimal disturbance to the soil, and so less germination of alien seeds.
Another way of destroying the bud bank of a plant that is too big to clip is to peel the bark down to just below ground level, pulling outwards. In order to have enough bark to hold on to, saw the tree off at 30cm above ground level and peel from the top.
Herbicides will destroy large plants with bud banks or lignotubers. First, saw the trunk of the plant off at ground level. Then, immediately dab herbicide onto the trunk.