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Kenya scientists discover invasive snail damaging rice farms

The Apple snail is extremely invasive.
Image: Cabi

Kenyan scientists discovered an invasive snail that was damaging rice farms. Given the impact of this species in Asia, there is need for an assessment of the risk to Africa, and the implementation of an appropriate response in Kenya and elsewhere to manage this new threat to agriculture and the environment, said experts.

Theophilus Mutui, managing director of Kenya Plant Health Inspectorate Service (KEPHIS) said Thursday that the apple snail, scientifically known as ‘Pomacea canaliculata’, threatens Kenya’s rice production especially in Mwea region where over 70 percent of Kenya’s rice is grown.

The snail is widely considered to be one of the most invasive invertebrates of waterways and irrigation systems. Mutui said that since it was first detected in Mwea irrigation scheme in central Kenya, the snail has spread gradually to other parts of the country.

The pest has infested more than 550 acres of rice, mainly in Ndekia and Tebere sections.

Kephis said more than 1,500 acres of the bordering lower areas that receive water from upper units are also at risk.

Although farmers sighted the snails as early as February last year, the discovery is only confirmed through a scientific process.

“Samples of snails and associated egg masses were collected and sent to Cabi laboratories in the UK for molecular identification,”  the Centre for Agriculture and Biosciences International, a UK-based scientific group, and Kephis said in a joint statement.

Golden apple snails have muddy brown shells and golden pinkish or orange-yellow flesh.

They are bigger and lighter in colour compared to native snails. Their eggs are bright pink.

The Kenya Plant Health Inspectorate Service said the snails have been observed in large populations, especially in the canals and paddies. They spend most of their lives submerged in water or mud, emerging only to occasionally forage, mate and lay eggs.

In the absence of water, they bury themselves in the mud and hibernate for up to six months and reemerge once conditions become favourable.

Last year, Mwea Research Centre manager Vincent Koech advised farmers to keep fields drained in the first 30 days of rice plants, when they are most vulnerable, or simply transplant 25-30-day-old seedlings from low-density nurseries.

The snails have been reported to cause up to 80 per cent destruction of the newly transplanted rice in parts of Asia and South America.

The scientists published their findings in the ‘First report of the invasive apple snail, Pomacea canaliculata in Kenya’ in the CABI Agriculture and Bioscience journal.

Apple snail is listed among ‘100 of the world’s worst invasive species. But they can be controlled with biopesticides. However, manual collection of snail eggs is preferred because the effective pesticides are also toxic to aquatic animals such as fish and tadpoles.

Farmers in Kenya are already talking about the damage caused to rice in Mwea, where over 70 per cent of the country’s rice is grown.

To manage the spread of the snail, local farmers will be trained, the public will be made aware of its dangers, physical barriers will be installed, and the use of mechanical control and community-based snail management will also be promoted.

Ivan Rwomushana, senior scientist, Invasive Species Management at the Nairobi-based Centre for Agriculture and Biosciences International (CABI) said that the findings show that other irrigation schemes in Kenya are still unaffected, although seed and machinery brought from Mwea poses a risk for invasion.

“We will work with the relevant national agencies to develop a rapid response and containment strategy to tame this new invasive species,” Rwomushana said. The snail has become an agricultural and ecological pest, causing significant economic losses in wetland rice cultivation and threatening biodiversity in Asia. The snail is listed among 100 of the world’s worst invasive species.

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