Zimbabwe Revives Key Water Bodies Using Biological Control to Combat Invasive Weeds

Water Weeds blooming in the water

Reporter

The Ministry of Lands, Agriculture, Fisheries, Water and Rural Development has successfully implemented biological control methods to combat invasive aquatic weeds in Chinyika Dam 2 in Goromonzi and Lake Chivero. This innovative approach not only addresses the pressing issue of weed infestation but also promotes environmental sustainability, highlighting the potential of natural solutions in managing ecological challenges. Aquatic weeds, particularly Kariba weed (Salvinia molesta) and water hyacinth (Eichhornia crassipes), pose significant threats to Zimbabwe's water bodies. These invasive species reduce available oxygen, obstruct recreational activities, clog irrigation systems, and degrade water quality. They have emerged as a major concern for local communities that rely on these water sources for fishing, irrigation, and recreation.

A Research Officer under Agricultural Research, Innovation and Specialist Services, Mr Nathan Sangombe, overseeing the biological control of invasive species, shared insights into the program initiated in March 2023. “We released a total of 1 400 Kariba weed weevils. The dam was 100 percent covered by the weed, so we developed a biocontrol program and released these weevils gradually over four months,” he explained. This strategic release was designed to ensure that the weevils could easily access one another for mating, thereby increasing their population densities effectively. As the seasons changed, Sangombe noted that the population densities grew slowly due to lower temperatures. “As we approached the warmer months of August and September, we began to see increases. By June 2024, we were getting approximately 2 000 weevils per square meter, leading to significant clearing of the weeds,” he said.

The success of this biological control program underscores the effectiveness of natural methods in managing invasive species.

“If people can witness how biological control works without chemicals, it shows the potential to restore aquatic ecosystems without harming the environment, humans, or livestock,” Mr Sangombe emphasised. This approach not only helps in managing the weeds but also aligns with global sustainability goals, promoting a healthier ecosystem. Community involvement is crucial for the success of such programs. Mr Sangombe urged all stakeholders to collaborate in the fight against invasive species. “For biological control programs to be successful, we need an integrated approach, with local communities taking ownership.” His call to action highlights the importance of collective effort in environmental stewardship. A researcher from Rhodes University, Dr Gerald Chikowore, said weed infestations affect water quality because they thrive in nutrient-rich systems. “The presence of these weeds indicates that the water is compromised,” he said. He stressed that the impact of invasive species extends beyond aesthetics, affecting the entire aquatic ecosystem and the organisms that depend on it.

Farmers have also expressed hope for the future. Zimbabwe Farmers Union Vice President Mr Fidelis Gweshe said he is positive that the weeds will not thrive again.

“I’m happy about the clear water we are now getting from the dam. We encourage our farmers to avoid farming too close to the dams to prevent further issues like siltation.” His comments reflect the positive changes occurring in the community as a result of the biological control efforts. As the Ministry continues its efforts to rehabilitate irrigation systems, they strive to enhance food security and livelihoods for farmers dependent on these water sources. Plant Protection Research Institute acting head, Mrs Grace Hama, said the programme is showing positive results. “We started our project of releasing bio-agents against water hyacinth in November 2023, and we are seeing positive results. We hope to clear the weeds within a year,” she said. The effective use of biological control methods not only revives vital water bodies but also sets a precedent for sustainable environmental management in Zimbabwe. By embracing natural solutions, the Ministry is paving the way for future initiatives that prioritise ecological balance and community involvement, ensuring that both people and the environment thrive together.