Rhizome scale

when you lift ginger or turmeric, look hard at the rhizome — the fat underground "hand" you dig up to eat and sell. An attacked rhizome is crusted with tiny circular grey scales, thickest around the buds and eyes (the growing points). Badly hit rhizomes turn light, wrinkled and shrivelled, feel dry and papery in the hand, lose weight, and seed rhizomes kept in the store fail to sprout.

each scale is a hard, flat, circular cap, grey to grey-brown, about the size of a pinhead (1–2 mm across) — smaller than a match-head. It does not move, even when you touch it. Flick one off with a fingernail and you find a soft yellowish body underneath and a pale mark where it sat. They sit stuck fast, packed close together in the skin grooves and around the buds.

with plain soil or dirt (that rubs off when the rhizome is wet — scales stay stuck fast and are perfectly round discs you must flick off); with mealybugs (white, soft, fluffy and powdery, and they crawl — scale is hard, flat, grey and fixed in place); or with the natural corky scars on old rhizome skin (flat rough patches, not raised discs you can lift with a nail).

start once the rhizomes are bulking up underground — from mid-season through to late season — and check hardest at harvest, then every month the crop sits in storage, because dry storage is when scale numbers explode.

cross the plot in a large "W" shape so you cover all four corners and the middle, not just the edge by the path. At about 10 stops, gently scratch the soil away from the base of one clump to bare the top of the rhizome, and look closely around the buds and eyes for circular grey scales.

don't just spot-check. Look over the rhizomes as you lift and sort them, and in store pull a handful from the top, middle and bottom of several bags or heaps and inspect them in good light — a few flat grey scales are easy to miss in the shade.

if you find those circular grey scales on even 1 rhizome out of the 10 you check — or on any rhizomes at all at harvest or in store — treat the whole lot as infested and act now. Unlike leaf pests there is no "safe" small number: a few scales quietly become a thick crust in dry storage.

the scale travels on seed rhizomes, so plant only clean, plump, scale-free rhizomes and reject any with grey crusts around the buds. Clean seed does more to protect you than any spray, because the armour cap makes the insect hard to kill once it is already there.

when you find crusted rhizomes at harvest or sorting, pull them out and destroy them — burn or bury them deep, never toss them on the field edge or keep them for seed. And rather than planting ginger or turmeric straight back on the same land, give it a season under a different crop (anything but ginger or turmeric) to starve out any scale left behind in the ground.

clear old rhizomes and crop trash out of the store before you bring the new crop in, keep seed in cool, well-managed conditions rather than long dry storage where scales multiply, and inspect the store every month. Dry storage is the scale's best friend — don't give it one.

if a rhizome you want to keep is only lightly crusted, rub or brush the scales off (they are fixed in place, they won't run away) and set that rhizome apart from your clean stock; throw out anything heavily shrivelled. Cleaning and sorting by hand is the step to try before reaching for any chemical.

when scales are present and hand-cleaning is not enough, dip the seed rhizomes in an approved insecticide solution — a "dip" means soaking them for the time given on the label, not spraying — before you put them in store and again before planting. Use only a recommended product at the exact label rate. Safety: wear gloves and cover your skin, eyes, nose and mouth; mix and dip in a shaded, airy spot away from food, drinking water, children, animals and bees; keep the used dip away from ponds, streams and wells; dry the rhizomes where people and animals can't reach them; and wash your hands, tools and clothes afterwards. Keep dipped seed clearly set apart so no one eats or sells it, and if you ever treat rhizomes meant for eating, respect the pre-harvest interval — the number of waiting days printed on the label between treating and eating or selling.

if you dip season after season, rotate to a different chemical group (a different active ingredient — the name is on the label) each time, so the scale does not slowly stop responding to the same one. That build-up of survivors a chemical no longer kills is called resistance.

if scale still creeps through your store despite dipping, don't try to rescue badly-crusted, shrivelled rhizomes — sort them out and destroy them to save the rest, and start next season with clean, certified seed from a trusted source. When a whole seed lot is heavily encrusted, destroy it rather than plant it — planting infested seed just carries the scale, and up to 40% of your crop's weight and value, straight into the next season.