Stem and bulb nematode

young onion and garlic leaves and stems push up swollen, twisted, bent and stunted, often paler than the healthy plants around them; beans show thick, distorted stems. The plant looks puffed-up and deformed even though nothing has bitten it — it has swollen from the inside.

gently squeeze a suspect bulb — an infested one feels soft and spongy, not firm. Cut it across and you'll see brown rings in the flesh with soft, discoloured layers; garlic cloves split, shrink and go brown. Later whole plants yellow and topple, and bulbs that looked healthy at lifting rot in the store.

A nematode is a worm far thinner than a hair — far too small to see without a microscope. The only trace you may catch is on badly infested, drying plants, where the worms clump into a whitish, cottony fuzz called 'eelworm wool' on the surface of rotting bulbs and stems.

basal rot and white rot begin at the root-plate at the very bottom of the bulb (white rot also leaves tiny black specks like poppy seeds). This nematode does the opposite — it bloats and twists the tops and leaves brown rings inside a soft bulb. Thrips, drought or weedkiller can curl leaves too, but they don't turn the bulb soft and brown-ringed with no insect anywhere in sight.

there is no 'safe number' of these worms. Even ONE patch of bloated, twisted plants — or ONE soft bulb with brown rings inside — means it is already here. Treat that single find as your signal to act on clean seed and rotation now, before it spreads further.

Before planting, sort through every onion set, garlic clove and seed and throw out any that are soft, spongy, browned, split, shrivelled or dusty with 'wool'. The worm rides inside the sets and cloves, so one bad lot plants the trouble straight into clean land.

look hardest from emergence through early growth — the seedling and early-development stages — because that is when the worms invade and when swollen, twisted, stunted seedlings first show. Cool, wet weather and low, damp corners of the field make it worse, so search those spots first.

so you cover all four corners and the middle, not just the edge by the path. Make about 10 stops; at each, pull a few suspect plants and cut open two or three bulbs to check for soft flesh and brown rings. The pest spreads outward from a starting point, so mark and watch any patch of stunted, deformed plants.

if about 1 in 5 bulbs is soft with brown rings inside, that block is badly infested — save none of it for seed or replanting, and don't carry its soil on your tools into a clean field.

where a recommended protocol exists, soak garlic cloves and onion sets in hot water before planting to kill the worms hidden in the tissue. Follow the recommended temperature and time exactly — too hot cooks the clove, too cool spares the worm — so use a thermometer and treat only clean-looking material.

registered nematicides (poisons made to target nematodes) only partly knock this pest back — they never clear it, and clean seed plus rotation still do the real work. Reach for one only as backup on top of those, never in their place.

these are among the most poisonous farm chemicals. Cover your skin, eyes, nose and mouth, apply in the cool of the day with the wind at your back, and keep it well away from food, drinking water, children, animals and bees. Respect the pre-harvest interval — the set number of days you must wait between the last treatment and harvest so no poison is left on the food. Wash yourself and your clothes straight after, follow the label, and rotate to a different chemical group each time so the pest never builds resistance.

you cannot spray this worm out of the soil. If a block stays infested, stop planting host crops there for several years, rest it or rotate it to non-hosts, and start fresh on clean ground with clean certified material. Lift and destroy badly infested plants — burn or bury them far from the field, never compost them beside the crop — and accept the loss on that block rather than carrying the worms across your whole farm on soil, tools and seed.