Herbicides

Herbicides

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.

Challenging plants

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.

Chemical removal

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.

Resources

Resources

Guides to Controlling Invasive Species 

* General Alien Invasive Plant Control

A 41-page booklet produced by eThekwini Municipality (Durban, South Africa) discusses general alien invasive plant control. Different methods of control are discussed in detail.

* Controlling invasive water hyacinth 

This 31-page booklet provides insight into best practice, removal methods, training and equipment to deal with invasive water hyacinth (Eichhornia crassipes). While produced for the eThekwini Municipal Area, this booklet is most useful anywhere water hyacinth needs to be controlled.

* Using herbicides to control plants

National Resource Management Programmes (NRM) is a division of Environmental Programmes, Department of Environmental Affairs, South Africa. NRM includes Working for Water, Working for Wetlands, Working on Fire, Working for Forests etc.  As the country's largest users of herbicides in their terrestrial invasive species programme, NRM experts have created guidelines and policies for using herbicides in South Africa. 

* Biological control of aquatic weeds 

Biological control as an integrated control method in the management of aquatic weeds in an urban environmental and socio-political landscape.

Case study: City of Cape Town.  147 pages.    By Louise Stafford (Masters Thesis, Rhodes University)