Spiny bollworm

a soft shoot tip that suddenly wilts, droops and dies — this is called a 'dead-heart'. Snap the wilted tip open and you will find a small caterpillar and a tunnel packed with moist, sawdust-like droppings (frass) boring down the middle of the soft stem.

look for round entry holes plugged with frass on the flower buds and young pods. Buds and flowers with a borer inside drop off the plant; bored pods grow twisted, bent and lumpy, and when you cut one open you find the caterpillar and its tunnel inside — the pod is spoilt and cannot be sold.

short and stout, up to about 1.5–2 cm long, brownish-grey to greenish, with a row of fleshy spiny bumps (warts) along its back — those little spines give it its name — and pale white or orange markings. The small moth is easy to know too: E. vittella has a bright green wedge or band down each front wing, while E. insulana has plain pale-green front wings.

with the big American bollworm (Helicoverpa), a large smooth caterpillar that sits on the outside chewing wide open holes in buds and pods, or with aphids and jassids that only suck sap on the leaves. The spiny bollworm is the one that tunnels inside — a wilted shoot tip or a frass-plugged hole is its signature, not open chewing on the surface.

start checking from when the plant is building its frame and the shoot tips are soft (the development stage, roughly 4–6 weeks after sowing), and keep it up hardest through flowering and podding (mid- and late-season), when the pods you sell are forming. Warm, humid weather (about 20–35 degrees C) pushes the pest fastest.

twice a week, walk a large "W" across the field so you cross all four corners and the middle — not just the row nearest the path. Make about 10 stops along the way.

look at 10 plants — check the shoot tips for wilting dead-hearts, and the flower buds and young pods for frass-plugged entry holes. Count how many of the shoots and pods you check are bored.

act once about 1 in 20 shoots or pods (5%) are bored — that is roughly 1 damaged shoot or pod for every 20 you check — or at the very first dead-heart shoots while the plant is young. Because you pick okra every few days and each caterpillar spoils a whole pod, don't wait longer. Fresh, moist frass means the caterpillar is still inside and feeding; old, dry frass in an empty tunnel is a past attack — don't spray for that.

don't plant okra or roselle straight after okra, roselle or cotton, and at the end of the season pull, clear and burn the old stalks — that is where the caterpillars and pupae survive to attack the next crop. Rotating to an unrelated crop starves the pest before you even sow.

the moment you find a dead-heart or a frass-plugged pod, clip off the bored shoot below the damage, pick off every bored bud and pod, and destroy them all (burn, bury deep, or feed to animals) — caterpillar and all. This is the single most effective thing you can do by hand: it kills the borer hidden inside and stops the next generation. Pick your pods young and often (every 2–3 days) so pods never sit long enough to be tunnelled.

while the caterpillars are small and still on the surface, spray Bacillus thuringiensis (Bt, a natural soil bacterium that kills only caterpillars and is safe for people, bees and the tiny wasps that eat the borer) in the cool of the day, aimed at the shoot tips, buds and young pods. Small parasitic wasps and other natural enemies also attack the borer — so avoid broad, harsh poisons that wipe them out.

only if bored shoots and pods keep climbing past the threshold, use a recommended product from the spinosyn group (spinosad) or an avermectin (emamectin benzoate) — these reach the small caterpillars before they bore in. Aim the spray at the shoots, buds and young pods where the young caterpillars feed. A spray cannot reach a caterpillar already sealed inside a shoot or pod, so it must go on early, while they are small.

cover your skin, eyes, nose and mouth; spray in the cool of the morning or evening with the wind at your back; keep the spray off open pods, off drinking water and rivers, and away from children and bees (spray in the evening after bees have left the flowers). Because you pick okra every 2–3 days, choose a product with a short pre-harvest interval — the number of days the label says you must wait between the last spray and picking — and respect it: never pick or sell pods sprayed inside that waiting time. Wash yourself and your clothes afterwards.

don't lean on one spray — rotate to a different chemical group each time (for example spinosad one round, emamectin the next) so the borer never gets used to it, and always lean on clipping, clean-up and Bt first so you spray as little as possible.

if bored pods keep climbing despite clipping and spraying, tighten your picking to every 2 days, widen your clip-and-destroy to the whole block, and at the end of the season pull and burn every okra, roselle and cotton stalk so no caterpillars carry over. Try to plant next season's okra well away from this field and away from any cotton, so the moths cannot simply walk across, and encourage neighbours to clear their old stalks too.