Toxic weed invades Mweya in Queen Elizabeth Game Park

A notorious weed, which was last seen in Kasese district a decade ago, has resurfaced. The South American weed, which was transported into Uganda through food donation support, has now displaced native plants in Mweya, a popular tourist peninsula within the heart of Queen Elizabeth National Park. 

As a result, antelopes, and the preying lions have abandoned this vital part of one of the country’s major tourist-attraction centres. Gerald Tenywa explores. 

In Queen Elizabeth National Park, Kenneth Karungi, a visitor from Kampala, likes what he sees. The army green plant with white flowers makes part of the game park look like a big beautiful flower garden. 

Despite its flowery beauty, the wild plant is hiding a poisonous reputation that hurts human beings and wildlife. It also chokes other plants by applying what botanical scientists dubbed “chemical warfare.” 

Using this aggressive chemical warfare, the weed that initially dotted roadside pavements leading to Kasese district 10 years ago, has now spread into the game park and eaten into the Mweya wild lands. 

The plant, scientists said, releases toxins called allergen or parthenin, which it directly injects into competing plants. 

Although game rangers have not reported any wildlife death related to the aggressive weed, experts said animals, such as antelopes, warthogs and lions, have since moved away from Mweya as the weed takes centre-stage. 

“It is difficult to see wild animals in areas where encounters with them were common,” Karungi said. 

Dennis Omondi, a resident of Katunguru fishing village, said scientists have told the community that the invasive poisonous weed is called Congress weed. 

Its scientific name, Omondi added, is Parthenium hysterophorus. According to the United Nations Food and Agricultural Organisation (FAO), an invasive weed is an alien species that disrupts or poses a risk to the ecology and biodiversity of a place, given its ability to out-compete other plants. 

Apart from death, the weed can poison milk and meat of any animal, including livestock that eats it, according to experts in a paper titled, Harmful and beneficial aspects of Parthenium hysterophorus. Within 28 days, experts said, the weed produces 15,000 seeds, making its multiplier effect aggressive. 

The same paper, published by the US’ National Institute of Health (NIH), states that the weed causes allergies and asthma in humans. 

According to the African Journal for Agricultural Research, Congress weed is among the 10 most noxious weeds on earth.

Impact on game park  

Asked about how the size of the area covered by the weed, John Makombo, the director conservation at Uganda Wildlife Authority (UWA) said: “What we know is that the most critical area that has been affected in the game park is Mweya. 

The weed is also affecting other parts of the park, but we are not sure of the total area of the park that has been affected.” 

In addition to Congress weed, UWA officials said they are also battling 10 other invasive weeds that have captured different parts of the game park. 

According to Makombo, Congress weed has brought a new measure of aggressiveness that remains unprecedented. 

“We worked with the agriculture ministry to manipulate 40,000 hectares or 100,000 acres (100,000 football playgrounds), but the weed bounced back after a short time,” Makombo said. 

“The war against the weed has become a tricky affair and is likely to take longer than anticipated,” Makombo added. 

To tame its aggressive sojourn into the game park, Makombo said UWA has hired a consultant to assist the agency map out the area covered by the weed and also suggest control measures. Makombo said the weed is not palatable to wildlife.
 
“It has degraded habitats and the wild animals have gone away from Mweya. It affects the areas where it grows and such areas have become useless,” he said. 

Makombo added: “The weeds cover and colonise the place and displace the native plants. Once the wild animals are not feeding properly, productivity also declines.”

What has been done 

• Biological control with weevils 

Dr Eric Enyel, the chief warden of Queen Elizabeth, said they had worked with the National Agricultural Research Organisation. The team deployed weevils, but the impact has not been felt at Mweya Peninsula. 

• Mechanical removal 

The Uganda Wildlife Authority uprooted the weeds, but they grew back, because the weed produces many seeds, which mature fast. 

• Chemical application

This is not acceptable in a national park. We do not want to provide a solution, which will cause even a bigger problem.

• Goats eating weed

Goats from the local community at Katunguru and Lake Katwe have been observed eating the weed and they seem effective in areas of Katunguru and Lake Katwe. 

• Wait-and-see approach

The weeds could keep growing and after sometime they will die and provide organic manure to other plants that are favourable for the wild animals. 

• Research needed

According to Enyel, more research is needed to get the best approach to get rid of the weed. At the moment, UWA does not have a concrete solution to address Congress weed, according to Enyel.

Chemical warfare 

The Congress weed, experts said, releases chemicals or toxins that inhibit the germination, growth, survival, development and reproduction of other plants. 

This phenomenon, experts said, is known as allelopathy — a chemical warfare that leads to reduced yields and crop failure. Congress weed is native to South America, but has moved to as far as Australia, Asia and Africa, where it is spreading its tentacles in wildlife-protected areas, such as Serengeti in Tanzania and now in Queen Elizabeth National Park. 

As Congress weed invades the game park, experts said there is need for an urgent solution to combat the spread of the weed. 

While Congress weed was first reported in Uganda about a decade ago, experts said the country has not come out with bold steps to fight the weed or harness it. 

The weed, officials said, has also been traced to Uganda’s border towns in Busia and Tororo, as well as stopovers along the highway to Kampala.

“Currently, the weed can be seen flourishing on most highways and stopovers across the country. This is a reminder that millions of weeds could be on their way to the agricultural land,” an official from UWA said. 

Officials said just like India, where Congress weed got introduced with rice donations from the US in the 1950s, a similar trend could have introduced the weed into Uganda. 

“It is suspected that the weed has been transported across the region by wheels of vehicles. The weed is naturally dispersed by wind and running water or rain over short distances. It is also spread, with the help of human beings, through garden equipment, tools or stock feed,” Natukunda said.

What King Oyo says 

Commenting on conservation and tourism around Queen Elizabeth National Park, the Omukama (king) of Toro, Rukidi IV Oyo said: “I recently visited Queen Elizabeth as part of my efforts to highlight our tourism potential under my 25-year development plan.” 

He added: “During my visit, I was saddened to learn about the declining numbers of some of the most iconic wildlife in Queen Elizabeth National Park.” The King also highlighted poaching as a big challenge that should be addressed. 

Control measures 

According to the Centre for Agriculture and Biosciences International (CABI), “If prevention is no longer possible, it is better to make interventions when the infestation by the weed is still small. This means early detection and response.” 

“Biological control agents have been released in Australia and parts of Asia with some success. South Africa has applied for release of agents and trials are ongoing in Ethiopia,” CABI officials said. 

Apart from biological control measures, CABI officials said, hand pulling, mulching and digging out the roots of the weed with a hoe can be effective in fighting the weed. 

“The weed can be used to make bio-fertilisers and mosquito repellents and insecticides. However, integrated pest control management is the best intervention. This is because it brings out the strength of each intervention,” Nakutunda said. 

In his view, Stephen Muwaya, a consultant, said there are many weeds but each requires a specific strategy to fight it. 

“When we have new invasive species in the country, we need research to understand it; the dynamics on how it spreads and how to handle it. This information is then passed over to the agricultural extension workers and wildlife managers to fight the weed,” Muwaya said. 

He added: “What I can say is that research has not been a priority in this country. I think it is a gap which needs attention. This is important to describe the methods of control.” 

Muwaya also cautioned against the use of chemical to destroy the weed, noting that other chains of life in the eco-system might also be eliminated. 

“It is important to use organic approaches to sustain the agro-ecology and ecological systems,” he said. 

On his part, the executive director of UWA, Dr James Musinguzi said: “We have a lot of work on our hands because invasive species are displacing our animals, affecting their health and tourism. We are going to reduce and eradicate the invasive weeds from the protected areas.” 

Asked how it will be done, Musinguzi said: “UWA has come up with a strategy and plan covering 2025-2035 to overcome the weeds which are threatening the park. The strategy was developed after a baseline analysis. We know that it is going to be challenging to fight the weeds but the only way out is to fight back,” Musinguzi added.

Makerere research 

Makerere University researchers have undertaken studies about the Congress weed, noting that it has triggered a major concern for biodiversity within the game park. 

The weed, which Makerere scientists, such as Martha Natukunda describe as a “biological warfare” matures within 28-42 days with each plant producing up to 15,000 seeds. 

Natukunda co-authored a paper titled, Management strategies for the noxious invasive parthenium weed in Uganda, with five Makerere University researchers — Kevin Natukunda, Gerald Kyeyune, Sharon Tusiime, Isaac Agbemafle and Jenipher Bisikwa. 

She said a significant amount of 10%-50% of Congress weed in pastures can kill cattle and buffaloes. In the livestock industry, it reduces carrying capacity by 90%, taints livestock products, such as milk and reduces the quality of meat.