Books for Nature Lovers
Problem Plants and Alien Weeds of Southern Africa
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Review By: Farmers Weekly - 11 June 2010

HOW BAD IS THE WEED/ALIEN problem is South Africa? 

South Africa is one of few countries seriously threatened by alien plants, mainly due to history and a diverse and amenable climate.

The UK only has about 2000 plant species within its shores, of which about 12 are serious alien weeds. On the other hand, about 2000 of our total of 20 000 plant species are naturalised aliens. Nearly 200 of these are currently listed in the Conservation of Agricultural Resources. Act (CARA) regulations - 122 of them in Category 1 (declared weeds). The number is set to rise to 348 later this year when the new National Environmental Management Act (NEMA) regulations come into force. 

Alien weeds slurp up over 7% of our diminishing water resources - equal to the country's total use. They've invaded over 10 million hectares - an area the size of KZN - mostly land that can grow food. they cause the local and even total extinction of indigenous species, which seriously threatens biodiversity, and they cause many other headaches, from blocked rivers to fires. The cost of trying to contain them is debilitating. Every alien plant competes with indigenous species and erodes the balanced nature of the entire ecosystem. 

Which are the most 'dangerous' plants in the various areas? 
A 'dangerous' plant is one that's not yet a problem, but has the potential to become on under slightly different circumstances. Black wattle is on of the most widespread of these species and is found in all provinces, invading various biomes and climatic zones. 

Syringa is more widespread but not as dangerous. Port Jackson is in the top 10 and occurs mainly in the Cape, but it's contentious because it's used as firewood. 
Lantana is a serious established problem in the whole of the Eastern and subtropical regions, from Cape Town to Messina. Prickly pears areProsopis are serious weeds in the interior. Rooikrans, prickly pear, Chromolaena and poplars are the rest of the 'top 10'. 
Perhaps a weed like pom pom weed (Campuloclihum macrocephalum) is more dangerous, because even though it has been here for over 30 years, it has only recently gone berserk. The threat is enormous and great efforts are being made to eliminate it before it becomes too widespread and impossible to control. Keeping it out of KZN has become a major and so far, successful, project. 

Obviously not enough is being done to control the problem. But what is 'enough'? 
The battle against these plants will never end in total victory. It may be possible to eliminate some species if they're detected early enough, but for those that are well established, it's a challenge to keep them from eventually killing us. 
Biological control is probably the best, if not the only long-term solution, but this requires research and understanding and it doesn't totally eliminates plants or species; it simply keeps them down to manageable proportions. Everyone - gardeners, farmers, municipalities, governments - must recognise the problem , be able to identify the species involved and do everything they can to prevent their introduction and further spread. 
Each of us can play a part in destroying them ad pressurise the relevant powers to make the effort. With awareness comes action, and the more action, the better. 

Is the list of plants that pos potential threats getting bigger and why? 
The new list in the NEMA regulations will have 348 species as opposed to 198 in the current CARA lists. 

' Alien weeds slurp up over 7% of our total but diminishing water resources.'

This doesn't mean the number of serious alien invaders has suddenly increases, but the list has now been extended to include the few species that have recently emerged as problems as well as many others with the potential to become a problem if not managed properly. 
Awareness of these potential dangers can prevent problems occurring if suitable precautions are taken at the right time. 

Obviously South Africans aren't really aware of the threats? 
Most South Africans have heard of Lantana, for example, but not many would recognise other Category 1 plants on the lists. Few gardeners are aware of which plants in their garden are alien and which have the potential to escape and flourish in the wild. 
About 50% of all our seriously invasive alien weeds were originally introduced as garden plants. In Australia this figure is 60%! The challenge is to crate awareness so we can all work in the same direction, removing unwanted an unintended plants and concentrating on indigenous or proven, harmless alternatives. 
Government has several awareness-raising schemes with various partners. For example, the Working for Water Nurseries Partnerships Programme has a project called "Plant me instead", created to promote awareness in the horticultural industry and get it to send the message to gardeners. 

What are the weaknesses in control policies/strategies? 
The secrets of successful long-term control strategies are follow-up and maintenance. Often, an intensive and expensive control programme isn't followed up or maintained properly and this can create a problem that's worse than the original. 
It's vital that the site is revisited after an intensive clearance campaign, initially as a follow-up to remove any remaining weeds, but then to do regular maintenance visits and treatments over a period of several years. 
Often there's bare soil with remaining roots and seeds that will continue to germinate and flourish if not contained. Most farmers and gardeners know the phrase "one year's seeds equals seven year's weeds". 

Will biological control or integrated control ever replace chemicals? 
The key to long-term control is going to have to be biological. Chemicals are quick and effective, but are expensive and have other drawbacks. 
The long-term strategy will be to use biological-control agents wherever feasible and to use chemicals and physical means whenever necessary. This is a classic integrated approach. 

What's happening to the small, emerging farms? Could weeds get out of control there? Is anyone checking up? 
Again, education and awareness are the key to positive actions. Training emerging commercial farmers in the correct use of herbicides on their crops would be standard practice. But, to get them to spend resources in controlling alien plants on the rest of their farm is a different matter. 
The Department of Water Affairs and Forestry initiated the Working for Water campaign in 1995 and has done a huge amount of vegetation control in the country.

Although it has provided a large amount of employment in the rural sector and would've had clearance programmes in all parts of the country, it's the follow-up and maintenance that's crucial to effective long-term control. 
Follow-ups usually become the responsibility of the landowner and this is where things go wrong. 

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