Invasive snail wreaking havoc on rice farms in Mwea

Kenya's basmati rice is on the verge of losing its sweet smell due to an invasive apple snail that is causing havoc on rice farms.

A study by the Centre for Agriculture and Bioscience International (CABI) in the Mwea Irrigation Settlement Scheme in Kirinyaga County reveals that the pest is wreaking havoc in fields.

CABI, under the Plantwise Plus programme, collaborated with the National Irrigation Authority (NIA), Mwea Irrigation Agricultural Development (MIAD) and the Kenya Plant Health Inspectorate Service (Kephis) on a socio-economic survey of players in the rice production sector in Mwea.

The study sought to investigate the presence and quantify the impact of the pest, scientifically known as Pomacea canaliculata, as well as to find out the apple snail management practices employed by individual farmers.

The report, compiled by Fernadis Makale, a research officer specialising in invasive species management at CABI, and Harrison Rware, a monitoring, evaluation and impact assessment specialist, indicates that the pests are a big threat to rice production in the region.

Affect production

The report, “Why the invasive apple snail is causing Kenya's basmati rice to lose its sweet smell of productivity", says the pests may affect production in the 30,000-acre scheme, of which 22,000 acres have been developed for paddy rice production.

"Despite a recently reported increase in production by 44 per cent due to enhanced mechanisation, increased cropping intensity and increased area under production due to enhanced on-farm irrigation water management, this is under threat due to the presence of invasive pests," the report says.

One of the invasive pests in Kenya is the golden apple snail, which was first reported in the Mwea scheme in 2020 by CABI scientists.

First case

Extension workers, agro-dealers and farmers reported that the first case of apple snail invasion occurred in Kimbimbi in 2020.

It is not clear where the pests originated from, but multiple accounts exist on the invasion route and most extension officers and media reports show that the apple snail was introduced by researchers from a local university as a rice weed biocontrol.

The pest has, since its discovery, spread to over 90 per cent of the scheme and out-growers and is still spreading as a result of equipment lending and water flow in the canals.

"Infestation levels of over 50 per cent have been reported in some units of the scheme started in 1954,” says the report, which added that the pest also affects other crops such as arrowroots.

Labour and production costs

The impact of the pest is causing more pain for farmers, who have reported an increase of about 10 per cent in labour and production costs.

"Farmers in the scheme have also reported crop damage of around 50-80 per cent with more damage reported in the directly seeded crop and newly transplanted rice."

Pest management has almost doubled farmers' production costs, the report says, especially on labour, purchase of plant protection inputs and replanting.

"On average, a total of Sh20,000 per hectare for pest management has been introduced – especially on labour for collecting and crushing snails – eating into the farmers' profit," the report says.

"There is no particular remedy that is formalised to manage apple snail. Therefore, the only advice they [agents] give to farmers is draining off the water canals and paddy fields to expose the snails to harsh conditions and other predators."

Control measures

The extension agents have suggested a raft of recommendations to deal with the pest, including creating barriers in feeder lines to trap the snails, alternate wetting and drying, draining the paddy fields, cleaning canals, handpicking and physical crushing of the snails and their eggs.

Levelling the field and fallowing are also recommended along with banding, as well as digging furrows at the end of farms so that the water in the furrows traps the apple snails.

But despite these efforts, the report says, the apple snail problem is still spreading.

Urgent joint efforts

"It is a situation that calls for urgent and joint efforts from all players to contain the problem before it spreads to other rice irrigation schemes in Kenya and the region."

In the past, birds and rodents were ranked highly as pests in rice production, but the emergence of the apple snail poses threats to the total income from rice farming as the pest’s effects start right at the nursery level.

Farmers say the available management options are proving to be insufficient and ineffective in tackling the pest.

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