Papaya mealybug

the newest leaves at the growing tip crinkle, curl and yellow, and the top of the plant goes bunched and stunted instead of pushing out healthy new growth. Where the pest feeds, a sticky, shiny honeydew (its sugary droppings) drips onto the leaves and fruit below and soon turns into a black, sooty mould — a dark grimy film that grows on the sugar.

part that mess and you'll find thick, cottony white clusters, like smears of cotton wool or a dusting of flour, on the leaf undersides, shoots and fruit. Inside the wax sit tiny soft yellowish, oval insects about the size of a pinhead (2 mm) — smaller than a rice grain — each dusted white, with a short, even fringe all around the edge and no long tails. Squash one and it smears yellow-orange, not red or pink. You'll often spot a fluffy cotton egg sac beside the colony and ants running over it.

Whitefly also makes honeydew and sooty mould, but its tiny white insects fly up in a cloud when you shake the leaf, while mealybugs sit dead still under their cottony wax. Plain sooty mould or powdery mildew rubs off dry with nothing living underneath and no stickiness — mealybug wax hides soft insects and leaves a sticky smear. Hard, dome-shaped scale bumps are stuck fast, have no loose cottony fluff, and don't wipe away.

start once your papaya is growing strongly and pushing out new leaves, and keep checking right through flowering, fruiting and up to harvest — this pest hits the growing and fruiting plant, not the tiny seedling. Look more often in warm, dry spells (around 22–33 °C), when it breeds fastest. On cassava and tomato, watch the same way from vigorous growth through to the crop maturing.

walk a big "W" across the block so you cover all four corners and the middle, not just the row beside the path. Stop at about 10 plants, and on each one check the growing tip and newest leaves (for crinkling), the undersides of the leaves, the shoots, and the fruit — especially where a fruit touches the stem, where colonies love to hide.

a line of ants marching up a stem almost always leads to a mealybug colony they are guarding — trace it to the source. Check first the plants nearest where you brought in new seedlings, cuttings or suckers, and any plant standing right next to one already infested.

carries white cottony clusters with sticky honeydew — or the newest leaves are just starting to crinkle — act now, don't wait. Because it spreads and hides so fast, those first few colonies are your best and cheapest chance to stop the whole field going.

the pest rides in on infested planting material, so only plant papaya seedlings, cassava cuttings and tomato seedlings from a clean, pest-free source, and never carry plants, suckers or tools from an infested block into a clean one. Keep the plot weeded, because weeds and stray host plants shelter the pest between crops.

the moment you spot colonies, cut off the heavily coated leaves, shoots and fruit and burn or bury them deep — never drop them on the ground or the rubbish heap, where the tiny mobile young (called crawlers) simply walk straight back onto the crop.

ants carry mealybugs from plant to plant and chase off the tiny wasp that would kill them, so cutting the ants off is one of your best moves. Smear a sticky band of grease or used oil around the trunk or stem so ants can't climb, and clear their nests from the base of the plant.

a tiny, harmless wasp called the Acerophagus papayae parasitoid (a parasitoid is a small wasp that lays its egg inside the mealybug, and its grub eats the pest from within) gives excellent, lasting, free control once it settles in. You can tell it is working when mealybugs turn brown and swollen ("mummified"), with tiny round exit holes. Ladybird beetles and lacewings feed on them too. Your job is simply to protect these helpers — control the ants and do not blanket-spray broad poisons that kill them.

on just a few plants, wipe or scrub the cottony clusters off with a rag, or blast them off the leaves and fruit with a strong jet of water. Done early, this alone can hold a light attack.

if colonies keep spreading, spot-spray only the colonies with a horticultural oil — a light plant or mineral oil that works by smothering the insect and dissolving its waxy coat on contact. It is a contact spray, not a systemic one (a systemic poison travels inside the plant's sap; a contact spray only kills what it directly wets). Add a little soap as a wetter to help it spread and cut through the wax, and wet each colony thoroughly, then spray again about a week later, because the wax sheds water and the young keep hatching. Never blanket-spray a broad-spectrum insecticide — it wipes out your free wasp and the pest comes back worse. Safety: cover your skin, eyes, nose and mouth; spray in the cool of the day with the wind at your back; keep the spray off food, off drinking water, and away from children and bees; respect the pre-harvest interval (the number of days you must wait between spraying and picking fruit to eat or sell, so no residue is left on it); and wash yourself and your clothes afterwards. If you ever step up to a stronger product, rotate to a different chemical group each time so the pest can't build up resistance (survive the spray).

stop any blanket spraying (it is killing your ally, the wasp), remove and burn the worst-hit plants to cut off the source, hit the ants hard, and give the parasitoid time — it can take a season to catch up, then it holds the pest down for good. When a plant is completely coated, bunched and stunted and its fruit is already spoilt, cut your losses: uproot or cut it down and burn it so it stops seeding the whole field, then replant with clean material.