Coffee berry borer

Look at the crown (navel) end, the tip away from the stalk: the borer leaves a small, clean, round pin-prick hole there, often ringed with fine pale powder (frass — the sawdust-like borings and droppings she pushes out as she digs). On the tree, badly attacked berries ripen unevenly and drop early, and the beans inside end up holed, mouldy and light, so they are downgraded when you sell.

Split a holed berry open and you will find tunnels bored through the bean, tiny white legless grubs, and small black beetles — often a whole family together. The beetle herself is tiny: about 1.5–2 mm, smaller than a sesame seed, like a full-stop of black ink — hard, shiny, and black to dark brown. On an unopened berry you usually see only her black rear end plugging the hole, head buried inside. Only the females fly and bore; the even-smaller males never leave the berry.

Every coffee berry has a natural dark, flat, star-shaped navel at the crown — that is not damage; a real bore hole is a fresh round puncture with powder, going deep. Coffee berry disease looks different: it makes dark, sunken, spreading rotten patches on the skin, with no clean hole and no powder. The antestia bug is a large shield-shaped bug that sucks the berry and leaves it misshapen and rotten — again, no neat bore hole. Remember: a powdery round hole at the crown = borer.

start once the small green berries have formed and begun to fill and harden, and keep checking every week right through ripening to red cherry. This mid- to late-season stretch — from filling berries to ripe cherry — is exactly when the female bores in. Be extra watchful in low, warm, damp, shady spots and near any old, unpicked bushes: the borer breeds fastest at 20–30 °C and at lower, warmer altitudes.

do not just check the row by the path. Walk a big "W" across the field so you sample all four corners and the middle — about 10 bushes. At each bush, pick 20–30 berries at random, from high and low and from inside and outside the canopy, favouring the riper, harder berries the borer prefers.

turn the crown (navel) end to the light and look for the fresh round hole and pale powder. Cut a few holed berries open to confirm the beetle or white grubs inside — that proves it is the borer and not disease. Also lift and check any dry leftover berries from last season on the tree and ground: they are the nest the new attack crawls out of.

count the bored berries. About 1 fresh hole in every 20 berries — that is 5 in 100, or 5% — is your action threshold. Reach it and you must move: tighten your clean-picking and bring in the controls below. Stay under it and just keep scouting weekly.

hang a few home-made alcohol-baited bottle traps (a bottle of spirit-scented water with a drop of soap) around the plot. A rising catch of flying females warns you a new wave is starting — the moment to tighten your picking. Traps only warn you; the 5% bored-berry count above stays your real trigger to act. Keep the spirit bait away from children and animals — it is poison.

The borer survives between seasons inside berries left behind, so never let ripe or over-ripe cherries linger on the tree — pick ripe berries frequently and completely all through harvest. This simple, timely picking on its own is the single most effective thing you can do — worth far more than any spray.

After the main pick, go back and strip every last berry off the tree — including the dry, shrivelled "mummies" — and gather every fallen berry off the ground. These leftovers are the nursery for next season's attack. Destroy what you gather: dunk it in hot or boiling water, bury it deep, or spread it in a thin layer in full hot sun, so the beetles inside die and cannot crawl back to your trees. Keep the whole plot tidy and free of stray berries.

Where holes are appearing, spray Beauveria bassiana — a natural fungus that grows on the borer and kills her — onto the berries, aimed at the females while they are still on the outside hunting for a place to bore in (it cannot reach those already sealed inside the bean). It is safe for you and for bees. At the same time, protect the borer's natural enemies — tiny parasitic wasps (harmless wasps whose young feed on the borer inside the berry) — by not blanket-spraying harsh poisons that kill them too.

Only if you are still over the 5% threshold after cleaning up should you reach for an approved insecticide (one cleared for coffee — check the label). It is a contact spray — it kills the female only where it lands on her, on the outside of the berry — so it works only if you hit her before she bores in, at the start of a female flush; once she is inside the bean, no spray reaches her. Safety: cover your skin, eyes, nose and mouth (long sleeves, gloves, a cloth over the face); spray in the cool of early morning or evening with the wind behind your back; keep it off food, drinking water, children, animals and especially bees; and wash yourself and your clothes afterwards. Respect the pre-harvest interval — the number of days the label says you must wait between spraying and picking — so no poison is on the cherries you sell or drink. And rotate to a different chemical group each time, or the borer builds resistance (it stops dying to a chemical used too often).

If holes keep climbing despite clean picking, the fungus and good sanitation, you have almost certainly missed a source of berries — re-check field edges, old unpicked bushes and fallen fruit, and ask neighbours to sanitise too, because females fly in from any dirty plot nearby. When berries are already heavily holed and dropping, accept that this season's bored beans cannot be saved — the beetle is sealed inside where no spray reaches her. Cut your losses the smart way: strip and gather everything now — spoiled berries and drops included — and destroy the lot. A ruthless clean harvest this season is exactly what starves the borer and protects next season's crop.