EA govts at a loss over how to fight off invasion of deadly, noxious weeds

In April, Kenya listed Parthenium hysterophorus as a noxious weed explaining that it has the potential to reduce yields in some crops by as much as 40 per cent.

“Because of the threat that this weed poses to biodiversity, agriculture and human health, the government of Kenya has declared it a noxious weed under the Suppression of Noxious Weeds Act,” read a statement at the Ministry of Agriculture.

Scientists at CABI-Africa, based at the World Agroforestry Complex in Nairobi, have termed it a “very harmful” invasive alien species (IAS) — having an impact on both human and animal health — and if eaten by livestock it can taint milk and meat.

Further, the scientists have warned governments in East Africa that they should be worried about weeds such as parthenium that have been coming into the region mainly through contaminated food aid or the horticultural industry.

Close to two decades ago water hyacinth, then reported in Lake Victoria, was the most threatening IAS in the region followed by Prosopis juliflora, known locally as Mathenge, cited in parts of Rift Valley.

The water hyacinth still occupies parts of Lake Victoria, while Mathenge has invaded an estimated 600, 000 hectares of land in Kenya.

But according to the scientists, parthenium is the most worrying.

“The weed, which has invaded more than 1 million hectares in Ethiopia, has the ability of reducing pasture production by 90 per cent, yields in crops such as sorghum by between 30 and 40 per cent and cause severe skin allergies and respiratory problems in 10-20 per cent of people that come into contact with the plant on a regular basis,” says CABI-Africa invasive species co-ordinator, Dr Arne Witt.

Respiratory problems associated with the weed include hayfever, asthma, and severe dermatitis.
The weed has also been detected in Uganda and Arusha, Tanzania.

The weed is abundant in Nairobi and infestations have been seen in villages and towns along the main road to the Ugandan border town of Busia.

The weed was first reported in Uganda about 20 months ago. It was recently reported to have invaded Queen Elizabeth National Park in Western Uganda, endangering animals and plants.

According to park conservationists, visitors could have brought the weed into the park about four years ago via Ethiopia or Kenya.

Despite looking beautiful, the weed is said to be among the world’s 10 most dangerous plants.

As the Global Environment Facility (GEF-Unep) project “Removing barriers to invasive plant management in Africa” — active in Ethiopia, Ghana, Uganda, and Zambia — came to an end in July, surveys revealed that more than 50 per cent of the invasive plant species in the EAC region have been intentionally introduced for horticultural or agroforestry purposes.

“Little is being done at any of these entry points – I travel regularly throughout Africa and have never been asked if I have any plants or animals in my possession,” says Dr Witt.

According to him, airports should have posters informing people that they must declare all plants and animals in their possession but most of them have no signage informing travellers that it is illegal to bring in plants or animals and their products.

Dr Witt wants the government to enforce its quarantine regulations and improve airport surveillance by ensuring that Customs officials not only focus on contraband but also thoroughly check visitors coming into the country carrying “these invasive materials” in their suitcases.

He says there are about 50-60 invasive plant species in the region which are invading forests, pastures, croplands, water bodies and protected areas.

According to research at CABI, agriculture, trade, and the environment are all being adversely affected by invasive alien species.

“These plants, animals and micro-organisms have escaped from their native environments and are spreading to new areas around the world. They now form the second biggest threat to biodiversity after habitat destruction and while this problem is not a new one, it continues to be a growing concern,” he says.

Curse of globalisation

Further, Dr Witt’s summary in a briefing paper titled “Africa invaded” states that globalisation of trade and travel is increasing the number of species moving around the world, and changes in land use and climate are making some habitats more susceptible to invasions.

It further shows that in Africa, many invasive species have been introduced both intentionally and accidentally and are now damaging natural and man-made ecosystems.

In his summary, Dr Witt says that various tropical South American water plants have invaded unique wetlands, lakes and rivers.

This has led to a loss of biodiversity and is affecting the local fishing and tourism industries. Terrestrial ecosystems are also being affected and agricultural production and food security are under threat.

“Red water fern for example, is rampant in a swampy belt in the Amboseli National Park,” he adds. If left unchecked, Dr Witt says the weed threatens to clog about seven swamps that serve the park and the community around it.

Prevention and mitigation of the effects of invasive alien species is especially challenging in Africa as there are many barriers to the effective management of invasive species, from weak policies and a lack of information and awareness, to inadequate prevention and control programmes.

“Yes, besides lack of resources to mitigate and prevent escalation of these species, most countries do not have a National Invasive Species Strategy and Action Plan – nothing is being done on a national scale to manage invasive species,” the CABI invasive species co-ordinator adds.

In view of this, Dr Witt says there is a need to strengthen policy, create awareness and build capacity.

“We need to develop integrated management strategies which incorporate chemical, mechanical, and biological control,” he said.

He indicates that more research needs to be undertaken on the costs and benefits of invasive plants but ironically “everyone talks about the benefits of prosopis (charcoal production and pods for animal feed)