All about keeping your farm snail-free

Snails are a menace to many farmers, especially during the rainy season, where they invade farms and ravage various crops. Recently, they have in their thousands attacked rice fields at Mwea Irrigation Scheme.

Magdalene Wanja spoke to Dr Paul Kinoti, the co-ordinator of Jomo Kenyatta University of Agriculture and Technology’s Bio Snail Project on how to deal with the creatures

Q1. There are various kinds of snails like the Giant African land snail, but according to farmers, the Apple snails appear to be more destructive. Why is this the case?

Golden Apple snails (Pomacea canaliculata) are the largest living freshwater snails with a diameter of up to 15cm and a mass of over 600g.

One of its major adaptation is its bronchial respiration system, which is comparable to the gills of fish located on the right side of the snail body, that enables it to breathe under water. 

In rice fields, the snails reproduce extremely quickly and eat young rice seedlings voraciously, causing significant economic damage to farmers.

Newly-transplanted rice seedlings are vulnerable to Golden apple snail damage for up to 15 days after transplanting or from four to 30 days after sowing for direct-seeded rice. They feed on the base of young seedlings.

They may even consume the young plants in a whole paddy overnight. They lay eggs on any vegetation, leaves, and objects such as twigs, stakes and stones, above the water surface.

The eggs hatch in seven to 14 days and the hatchlings are voracious feeders growing and maturing quickly. They lay 1,000 up to 1,200 eggs in a month.

They live in ponds, swamps, irrigated fields, canals and water-logged areas. They feed by scraping plant surface with their rough tongues, so they prefer young soft plant parts.

Q2. Apart from rice, what other crops are easily attacked by snails and why?

Beetroots, cabbages, lettuce, spinach, egg plants, pepper, potatoes, tomatoes and strawberries. This is because snails are drawn to nutrient-dense foods.

The deeper the green of the leaf and the more moisture it holds, the more appetising it appears to a snail. 

Q3. Snails are usually rampant during the rainy season or on farms with soils that are usually moist like rice fields. Why is this the case?

Both snails and slugs rely on moisture to survive. Their bodies dry out very quickly when they are active without moisture to support them

This is why they only become active when it rains or when the field is moist. In addition, most snails and slugs are typically active at night because it is cooler and more humid and there are fewer predators to hunt them.

If they know there is a food source nearby, such as the field of rice, they will hide until the dampness returns.

Yes, some snails can be harvested and eaten, but do they have any economic benefit on the farm as much as they are destructive?

Snails can be harvested and processed into various by-products such as organic fertiliser, animal feeds, skin care products such as soaps and creams.

They should not only be viewed as destructive creatures but also as possible generators of sustainable income.

Q4. Which is the best way to eliminate snails, without causing environmental pollution or endangering crops?

The best way is to use an Integrated Pest Management system. This approach uses strategies such as baits, traps, barriers and repellents, use of biological methods, selection and use of snail resistant plants, killing and disposal of the snails manually, changing the watering schedule and killing their eggs.

Pesticides are used only according to established guidelines, where they should target the organism only.

Pest control materials are selected and applied in a manner that minimises risks to human health, beneficial and non-target organisms, and the environment.

Taking the current Mwea Irrigation Scheme scenario where the Golden Apple snail population is out of control, biopesticide formulated from natural materials that not only has high knockdown effect but also with minimal or low toxicity to the human, environment and non-target organism such as fish will be most preferred.

One such a product is the Biomollusk, which is a bio-pesticide derived from Saponins of the Chenopodium quinoa. This product targets snails and slugs but is not lethal to fish.

Q5. Some people suggest use of ducks, egg shells or liming the farm, how effective are these methods?

Some of these methods are highly labour-intensive and may be unsuited to various areas. In addition, they are not highly effective in eradicating the snails.

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