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City Parks is on a search and destroy mission, with invasive alien plants in its targets. They inhibit the growth of indigenous plants and must be stopped.

The ubiquitous bugweed can be found on sidewalks, gardens, along freeways and streams and in many parks
The ubiquitous bugweed can be found on sidewalks, gardens, along freeways and streams and in many parks

JOBURG has been invaded by aliens. But instead of little green men, these are big green plants spreading their tentacles. Bugweed is the latest alien invasive plant to give the city a headache, but City Parks is fighting back.

"We are aware of the widespread occurrence of bugweed throughout the city on sidewalks, in gardens, on road islands, along freeways, along streams and in many parks," says the City Parks spokesperson, Jenny Moodley.

Bugweed, with the scientific name Solanum mauritianum, comes from South America and is a small shrub with leaves covered in white velvety hairs which can cause skin allergies and asthma. The fruit looks like berries and is poisonous when unripe.

It is highly invasive and inhibits the growth of indigenous plants. It can be controlled by pulling out the seedlings when they germinate, which is the easiest and cheapest method of control. Plants up to one metre in height can be sprayed with herbicide; larger plants need to be cut to ground level and re-growth treated with herbicide.

"Johannesburg City Parks has been mandated by the City to control alien plants, and it has an annual alien plant programme."

As well as controlling bugweed, invasives such as black wattle, lantana and blue gum trees are on the entity's hit list. Black wattle, which comes from Australia, is a declared invader category two according to the Conservation of Agricultural Resources Act of 1983. Plants in this category can only be grown if a demarcation permit is acquired.

It is a thornless tree with dark olive-green leaves and golden hairy growth tips. The fruit is a dark brown pod, which contains the seeds. Black wattle is highly invasive and is also classified as a transformer invader plant. In Johannesburg, it grows prolifically along streams, in disturbed grassland, on ridges and in gardens.

It can be controlled in the same way as bugweed, by pulling seeds out when they germinate, and cutting and spraying with registered herbicides. Stubborn is the black wattle's middle name, though, and seeds may continue to germinate at removal sites for many years, so close supervision is required.

Lantana is also an obstinate invasive plant, and needs to be treated in much the same way: with utter ruthlessness and plenty of herbicide. As a category one weed, legislation states that it needs to be controlled immediately. Hailing from Central and South America, its stem is covered with hooked prickles and the strong-smelling leaves can cause skin irritation.

It can be found countrywide along waterways, forest margins, degraded land and roadsides, as well as in urban open spaces.

Sidling up to the lantana along waterways and wetlands is the grey poplar, which originally came from Europe and Asia. Like black wattle, it is a category two tree and can only be grown with a demarcation permit. It is semi-evergreen, with white or grey bark and leaves that are dark green on top and grey or white on the bottom. Only the male tree flowers, and when it does, the flowers are reddish.

It can be controlled with foliar treatment, which involves spraying with herbicide. Under no condition should the seedlings be pulled because they are part of the root system. Trees over one metre should be cut to ground level, and the stump should be chemically treated.

Blue gum trees are also category two invaders. They are evergreen trees that grow to between 18 and 40 metres high. They have smooth grey bark; leaves are dark green, the flowers are cream and the fruit is red-brown. These trees invade water courses and the best way to remove them is to pull out the seedlings or cut them down and treat with herbicide.

However, controlling these invasives is no small task. The area covered by alien invasives includes not only parks and nature reserves, says Moodley. "To conduct a blitz here would be a mammoth and costly task."

In addition, City Parks' annual programme only covers certain ridges which have biodiversity value, such as Klipriviersberg Nature Reserve. "This is a small percentage of the Johannesburg area and it must also be borne in mind that this is budget-related," she says.

Despite these setbacks, the organisation is determined to move forward in its fight against these plants. As such, a biodiversity strategy and action plan has recently been completed by the City's environment management department. The recommendation of the plan is the development of appropriate policy and a framework for managing alien invasives.

This will give City Parks a clearer action plan, as well as annual budget requirements, Moodley explains.

In line with this, discussions between the City's environment department, City Parks and the Department of Agriculture, Forestry and Fisheries have been initiated, to appoint weed inspectors who will also be able to enforce alien plant legislation and by-laws. They are hoping that a result of this will be residents removing alien plants from their properties.

"Education and awareness is also a critical aspect if we are to successfully remove the invasive alien plants," she says.

City Parks wants to further train its field staff in the identification and removal of alien plants; for instance, if the street trees unit encounters invasive plants while trimming trees, it can remove them.

"We all need to work together towards a common goal and interact with all those involved in alien plant control," she says. "Bugweed and other invader plants cannot be successfully brought under control in Johannesburg without the help of residents, residents' associations, business, nurseries and organisations.

"Residents and business can make a big difference as the sources of infestations are often gardens. City Parks encourages all residents to become aware of these plants and to remove or treat them wherever possible," she says.

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