Wednesday, May 7, 2014

UST GS: Giant African Snail - A Pest in the Garden

Dr Abe V Rotor

Living with Nature - School on Blog
Paaralang Bayan sa Himpapawid (People's School-on-Air) with Ms Melly C Tenorio
738 DZRB AM, 8-9 evening class Monday to Friday

  Achatina fulica, two shades, two views; a colony of A fulica

Silently through the night an army of slimy hard-shelled land snails creeps over vegetables, ornamental plants and a wide variety of cultivated crops. The great attack begins!

The Giant African Snail, scientifically known as Achatina fulica is perhaps the most destructive land mollusk to agriculture, and ranks among insect pest and rodents. Believed to have been introduced into the Philippines by the Japanese during the Second World War as food, it has spread to almost all parts in the country. It is most felt in Batangas, Bulacan, Camarines Sur, Cavite, Laguna, Nueva Ecija, Nueva Vizcaya, Pampanga, Quezon, and Rizal where orchard crops are extensively grown.

Three days after hatching the young snails, roofed with semi-transparent shells, begin feeding on decayed vegetation and succulent plant tissues. The hatchlings emerge from eggs laid in round dugouts made by the adult snails. Except in size, frailty and color markings of the shell the young resemble the adults in all aspects. Adults mature in two years but begin to produce eggs after the first year. Around 195 to as many as 505 eggs are laid by one adult. Although hermaphroditic, it must copulate to enhance fertility of its eggs.

The gregarious snails sometimes in hundreds may be found attacking a single plant completely devouring its leaves, small stalks, buds and young fruits or may completely inhibit productive development of the plant. From the first rain in May to late December, they destroy plants of many kinds like coffee, potato, papaya, banana, and other food crops. In the absence of growing plants they feed on decaying fruits and refuse, on gummy sacks, cardboard and dried organic matter. They are oftentimes like rodents inside garbage cans. Their voracious feeding habit makes them adapted to a wide range of environmental conditions.

Protected with chestnut-brown shell made of six to seven whorls in clockwise spiral, this land mollusk is relatively safe from predators and parasites except for some red ants and predatory beetles. When in danger, it completely retreats into its shell, appearing like stones or part of a pile of rubbish or stones. Its senses of touch and smell are uniquely installed atop two pairs of telescopic knob-shaped antennae and as such a highly sensitive. Except for a pair of sharp cutting mandibles the body is all flesh. It moves sluggishly and quietly and it could not be traced if not for a slippery track of mucous secreted by the glands in the broad foot or sole.

But this nocturnal robber is most wanted during the day. Always a target of children and angry housewives and gardeners it dies painfully once its shell is fractured or broken. Young snails however, can mend slightly damaged shells.

But think twice before you kill or pitch them against the wall. Snails during the Japanese occupation were gathered for food. Have you ever tried snail rebasado? People living in tropical islands of the Indian and Pacific Oceans are collecting snails as food for themselves and their poultry. As feed for livestock and poultry it is a fair substitute for fishmeal. Dried snail meat when ground after cooking contains protein higher than the limit of 50% for meat and bone scrap, the commercial feed meal popular in the market.

Why don’t you have them repay for what they destroyed? The snail when dried and ground may be mixed with garden soil and allowed to decompose to permit bacterial and proteolytic enzymes to split the proteins into their corresponding amino acids which finally form into nitrates and other nutrients necessary for your garden crops.

Tropical leather leaf slug, Laevicaulis alte
If you are after large scale eradication of this garden and field post use metaldehyde snail bait which for several years now has not been locally replaced by any better bait preparation. One part metaldehyde mixed with 40 parts of rice or the Bureau of Plant Industry and other agricultural agencies abroad generally advocates corn bran moistened with a little amount of water. At the rate of one to two heaping tablespoonfuls the baits are placed on pieces of banana leaves or thick paper around bases or rows of plants, stone piles along fences, near piles of kitchen and farm refuse. Baiting is most effective at dusk or early morning. Avoid exposing the baits to direct sunshine.

There is another practical means of getting rid of this pest without much effort. Bait the snails at night with beer and gather them in the morning. Place the beer in a shallow container and bury it with its rim on level with the ground. A flat sardine can or an aluminum pan for leche flan is ideal. Be sure to replace the setup with the fresh beer evening and to gather the snails early the following day.

Don’t let this giant surprise you while you are sleeping. You may not have a good garden again this year. ~

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