Pod-sucking bugs

Look for tiny dark, sunken spots where the beak went in, and inside, shrivelled, shrunken or stained seeds (often brown- or purple-blotched). Badly hit pods stay flat and empty, bend or curl, and dry out early while the rest of the plant is still green — and a grey or black mould often grows right at the puncture spots.

the common one is the spiny brown bug — a narrow, dull-brown bug about 1 cm long (the size of a coffee bean) with two little spines poking out at the shoulders. The adults and their smaller wingless young — called nymphs — cluster together on the green pods, often right at the pod stalk. Squeeze or disturb one and it lets off a sharp, foul smell; that is why they are called stink bugs. A few in this group are shield-shaped and bright green instead of brown.

with the pod borer — a small caterpillar that chews a hole and tunnels inside the pod, leaving droppings and webbing the flowers together; pod-sucking bugs leave no entry hole, only pin-prick punctures and shrivelled seed. And unlike aphids (tiny, soft insects crowded on the shoots and growing tips), these bugs are bigger, firm-bodied, walk about openly on the pods, and fly off when you get close.

and keep checking right through pod fill (the mid-to-late season) — this is exactly when the bugs move in and do all their damage. Walk the crop at least twice a week, and more often in hot, dry spells, when the bugs breed fastest.

Look in the early morning while it is still cool, when the bugs are slow and sluggish and won't fly off before you can count them. In the heat of the day they hide low in the canopy or drop to the ground, and you will miss them.

Walk a big "W" across the field so you cover all four corners and the middle — not just the row by the path where you always look. Make about 10 stops, and at each stop check the pods on a metre of row (or on 10 plants): look on the undersides of pods, where pods cluster together, and at the pod stalks, and count every adult and wingless young you see.

During flowering and pod fill that is already enough to start eating into your harvest — don't wait for the pods to shrivel, because by the time you see that, the damage is done inside.

Plant early and all at once with your neighbours, so your pods fill and are ready before bug numbers build up. Clear the weeds in and around the field all season — wild legumes and other weeds are where these bugs breed and shelter between crops. And harvest as soon as the pods are mature: bugs pile onto the last drying pods left standing in the field.

Tiny wasps that kill the bug's eggs, plus ants, spiders and other predatory bugs, hold numbers down for free — so avoid routine broad, kill-everything sprays that wipe them out along with the pest. While the bugs are slow in the cool early morning, you can also hand-pick or shake them off the pods into a tin of water and drown them; going over a small plot a few mornings running can clear a light attack with no spray at all.

If you are over threshold at flowering to pod fill, use a contact insecticide — one that kills the bugs it lands on (unlike a systemic, which is taken up inside the plant and travels in the sap) — and aim it straight at the pods where the bugs feed. Protect yourself: cover your skin, eyes, nose and mouth, spray in the cool of the day with the wind at your back, keep the spray away from food, drinking water, children and animals, and wash well afterwards. Respect the pre-harvest interval — the set number of days you must wait between spraying and picking the pods — so no poison is left on the food you eat or sell.

Your crop is in flower, so bees are feeding on it — a midday spray on open flowers will kill them. Spray only in the late evening once the bees have gone home, and never drench open flowers in the heat of the day.

If bugs come back after spraying, rotate to a different type (group) of insecticide next time — using the same one over and over lets the bugs stop dying from it, which is called resistance — and tighten your weeding and harvest promptly. But once the pods are already shrivelled and drying, no spray will bring that seed back: cut your losses — harvest what has filled, dry it, and sort out the stained, damaged seed. Don't keep damaged seed for planting (it germinates poorly), and next season plant earlier and together with your neighbours to slip past the worst of the bugs.