Golden apple snail

in a newly planted paddy you find young rice cut off at the base and floating, with bare gaps and missing hills (the planted clumps of seedlings), so the stand looks patchy and thin. The snails feed at night, so the cut seedlings appear overnight.

look for clusters of bright pink to red eggs, like a clump of tiny pink pearls or raspberry grains, stuck just above the water on rice stems, weeds, sticks and the bunds (the raised earth walls around the paddy). No other paddy pest lays pink eggs above the water — this alone tells you it is golden apple snail.

a big, round snail with a golden-brown to olive shell, anywhere from grape-size to as big as a golf ball or small apple, the soft body often grey-to-orange. Find them in the water and on the mud at dusk and dawn, gathered in the low wet spots and near the water inlets.

with harmless native snails — those are usually smaller, and their eggs are white or jelly-like and laid under the water, never bright pink above it. Crabs and rats also cut seedlings, but they leave burrows in the bunds, not pink eggs and empty shells lying in the water.

The danger window is the first 2 to 4 weeks after transplanting or seeding — from establishment through early tillering (the young growth stages), while the rice is short and soft enough for a snail to cut. Check every day or two, best in the early morning or at dusk when the snails are up and moving in the cool.

Walk the bunds all the way round, then wade a big "W" across the paddy so you cover the middle and all four corners, not just the edge by the path. Look hardest in the deep low spots and around the water inlets, where snails collect.

At about 10 stops, mark out one square metre (about one big step each way) and count the snails you can see in the water and on the mud; at the same time scan the stems, weeds and bunds above the water for pink egg clusters, and check the seedlings for fresh cuts.

, or the moment you spot the first missing hills in a young paddy. In tender new rice even a few snails do fast damage — don't wait for the numbers to build.

every morning handpick the snails (concentrate on the channels, low spots and inlets) and crush them. Scrape the pink egg clusters into the water or crush them — eggs knocked under water cannot hatch — before they become hundreds of new snails. Lay papaya, cassava or banana leaves on the mud in the evening as bait: snails gather on them overnight, so you collect a heap at dawn. Push a few sticks into the paddy to give the snails one place to lay their pink eggs where you can find and destroy them. Once the rice is 10 to 14 days established and strong, herd ducks through the paddy — they love to eat the small snails.

if snails stay at or above 1 per square metre despite draining and picking, use a registered molluscicide — a snail-killing product approved for rice; where you can, start with a gentler plant-based type such as tea-seed cake (a natural saponin) before reaching for a harsh chemical one. Apply it in shallow water so the dose stays concentrated where the snails are, and spot-treat only the wet low patches and inlets where they gather, not the whole field. Molluscicides kill fish and other water life — keep them out of fish ponds, streams and drinking water, and never use one in a rice-and-fish paddy. Cover your skin, eyes, nose and mouth, apply in the cool of the day with the wind behind you, keep children, animals and bees well away, wash yourself and your tools afterwards, and respect the pre-harvest interval (the number of days the label says to wait between treating and harvesting). If you must treat more than once, rotate to a different molluscicide so the snails don't build resistance (stop being killed by it).

when a young paddy is badly hit and the hills are gone, don't lose the stand — replant the bare gaps with older seedlings straight away while keeping the water shallow; young rice recovers well if you gap-fill fast. And because these snails survive the dry season buried in the mud and return every year, clean up after harvest: collect the snails, crush the pink eggs, then drain, dry and plough the field, and screen your inlets again next season — that is how you stop them coming back.