Invasive alien plants: Identifying intruders timeously

In South Africa, an estimated 1,44 billion cubic metres of water is lost to invasive alien plants annually. To put it in perspective, this amount is enough to provide 3,38 million households consisting of four people with water for a year, or to irrigate 120 000ha of cropland (WWF, 2016).

Most South African producers are adept at keeping a finger on the pulse, but when a small patch of invasive plants makes itself at home on the farm, it can easily be overlooked. The culprits, known as invasive alien plants (IAPs), can establish themselves and spread like wildfire in the blink of an eye.

A spot of bother

IAPs can be brought into an area intentionally or unintentionally. Growing outside their natural habitat without natural boundaries and enemies, these plants can rapidly overtake farmland, catchment areas, conservation land, reserves and communal sites.

They can lead to innumerable environmental and economic losses, and cause devastation in terms of depleting precious water sources, displacing and killing the seeds of indigenous plants, changing plant community diversity and altering fire behaviour. Currently estimated to comprise more than ten million hectares, IAPs can also lead to vast quantities of monocultures, soil damage, excessive erosion and changes in nutrient cycling, to mention but a few.

Combatting invasive alien plants

While catching up on the latest available information on the topic of alien plant species, Agriorbit spoke to Llewellyn Collett, a project manager at Working on Fire. He currently manages one of the many drought relief projects that help clear invasive alien plants in catchment areas across the country – the project forms part of the drought relief programme in the Eastern Cape.

“First off, once the presence of an alien invader is identified, it is important that remedial action is taken as soon as possible. The longer the problem is allowed to get out of hand, the more it will cost to solve it,” remarks Llewellyn. “If left too long, the cost simply overwhelms farmers, especially considering the fact that we are all on a tight budget these days.”

Early detection and timeous action are critical points when tackling IAPs. Using the example of a small patch of black wattle growing somewhere on a farm in South Africa, Llewellyn cautions against the temptation of ignoring its presence.

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“While these plants are still growing at knee height, or below, it hardly ever receives a second glance. However, the trouble starts when it reaches shoulder height and the farmer wants to get rid of it. Removing these trees will cost a farmer three times more than what the initial costs would have been. This is why we need timeous action.”

Masterminding an action plan against invasive plants

An integrated weed management programme, depending on the nature of an IAP problem, is usually recommended and consists of numerous methods to eradicate different problems. It can include the following techniques:

Manual technique

• Basal bark treatment: A suitable herbicide mixed with a penetrant is applied to the target plant from a height of 250mm to ground level.
• Pulling by hand: A young plant is gripped as close to the ground as possible and pulled out by hand using gloves. Make sure the complete root system is pulled out.
• Ring barking: All bark must be removed from the bottom of the stem below ground level to a height of 0,75 to 1m.
• Frilling: An axe or cane knife is used to make angled cuts downward to the cambium layer through the bark in a ring; a herbicide must be applied to the cuts.
• Felling and removal of trees with chainsaws, bowsaws, brush cutters or cane knives.
• Cut stump treatment: Stems and trunks should be cut as low as possible before a herbicide is applied. The herbicide label will indicate how low a stump must be cut and how the solution of water and penetrant must be applied.
• Stem injection: Downward slanting holes are punched into the main stem, using a sharpened metal spike and injecting herbicide directly into the plant around the stem.

Mechanical technique

Mechanical and chemical methods are often used to get rid of alien plants, but it is important to use the correct methods to achieve the desired results. Equipment such as chainsaws, clearing saws, manual equipment, and loppers are common tools of the trade. The size of the area and type of plants determine equipment needs.

Chemical method

Here the correct product must be used at the recommended rate as per the label. When using chemicals, it is always advisable to contact the relevant herbicide representative who can advise accordingly. For example, the use of diesel is no longer considered environmentally friendly and the application of alternative adjuvants and penetrants, including vegetable oils, is recommended.

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Burning method

Burning is one of the most cost-effective methods in the fight against IAPs. However, an error that frequently occurs is the ‘quick solution’ of burning to get rid of unwanted vegetation. Unfortunately, some alien species, such as Port Jackson and black and longleaf wattles, rely on the heat from fires to assist in seed germination, causing dense re-infestation. These three species are commonly spread across the country and are extremely aggressive invaders, displacing most indigenous plants in its immediate surrounds.

Learning to control IAPs

In the war against invasive alien plants, producers have the option to empower and equip themselves and their workers by enrolling for training courses hosted by numerous private service providers throughout the country.

Llewellyn mentions that several different courses, such as those aimed at herbicide application and weed identification, usually run over short periods. “By using the Internet and simply typing ‘environmental weed management training’ into the search engine, you will find the names of all the different service providers,” he says.

Training is essential for farm workers who must deal with herbicides and dangerous equipment such as chainsaws. Llewellyn also believes that trained staff obtain a general understanding and appreciation for what they are doing. “Although the training is an expense, well-trained workers will increase productivity on the farm, which is an all-round benefit.”

Llewellyn suggests that farmers collaborate within their respective associations to approach service providers to facilitate training for a group, rather than for individuals. “It will drastically bring down costs, while everyone will be enjoying the same benefits,” he concludes. – Carin Venter, FarmBiz

For enquiries, contact the Department of Environment, Forestry and Fisheries on 012 399 9000 or visit https://www.environment.gov.za/contacts/provincial_offices
for access to the provincial offices.

Alien species in South Africa

A total of 559 alien species have been registered as invasive, and a further 560 species are listed as prohibited and may not be introduced into South Africa. The three-phase programme rolled out by the Department of Environment, Forestry and Fisheries consist of the following actions:

1. Initial control, which brings on a drastic reduction of an existing population.
2. Follow-up control where seedlings, root suckers and coppice re-growth is controlled.
3. Maintenance control that consists of annual control where a low number of alien plants are sustained.

Helpful websites

1. Categories of IAPs
2. List of IAPs in South Africa
3. Invasive plants in South Africa landowners asked to report