Oil palm bunch rot

a spread of white, cottony threads over the fruit bunch — like fine cobweb or a dusting of cotton — creeping down between the fruitlets and binding them together. Under and around the threads the fruit goes soft, brown and rotten, and the rot creeps outward from fruit to fruit across the bunch.

look first at the poorly-pollinated bunches (the gappy ones full of small, hard, seedless fruit) and the small aborted bunches left sitting in the crown — those are where the rot takes hold, before it spreads onto the good, full bunches next to them. A bunch left hanging too long past ripe rots the same way.

on a badly-rotted bunch, and on old bunch stalks and dead male flowers and trash in the crown, the fungus sprouts tiny white toadstools — little mushrooms with a slender stalk and a small cap, growing in clusters. That little mushroom is the disease making its spores to infect the next bunch.

with an ordinary over-ripe bunch (the fruit softens and browns, and loose fruit drops, but there are no white threads and no little mushrooms) or with rat and squirrel damage (gnawed, chewed fruit with teeth-marks, again no white mould). Ganoderma is a different disease — that one is a hard bracket at the base of the trunk, not on the fruit. Bunch rot is the one with the white cottony threads binding the fruit, and the tiny white mushrooms.

from flowering right through bunch-fill to harvest (the mid-season and late-season stages) — the whole time bunches are hanging on the palm. Step up your checks in the rains, and in still, damp weather, and in any block where the canopy is crowded and shady, because the rot loves warm, wet, airless conditions (about 24-32 degrees C and high humidity).

every 3-5 weeks, walk right through the stand — not just the edge rows — and stop at each palm to look up into the crown at the forming and hanging bunches, and at the trash caught among the frond bases.

go straight to the gappy, poorly-pollinated bunches, the small aborted bunches, and any over-ripe bunch held too long — hunt them for white threads, rotting brown fruit, and the tiny white mushrooms in the crown.

the threshold is the very first bunch you find with white threads or rotting fruit — 1 rotten bunch is enough to trigger action, because a bunch left in the crown throws the fungus onto its neighbours. On the same round, clear every aborted, gappy or over-ripe bunch on sight, before it starts to rot.

bunch rot is rarely worth spraying — sanitation and pollination do the real work. Only in a bad, spreading outbreak, and only on top of a hard sanitation round, use a recommended protectant (contact) fungicide on the bunches. "Protectant" means it coats and shields healthy bunches but cannot cure a bunch already rotting — so cut out the rotten ones first, then protect the rest.

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 the fruit you'll send to the mill, off drinking water and rivers, and away from children, and away from the flowering palms where the pollinating weevils work. Respect the pre-harvest interval — the number of days the label says to wait between the last spray and cutting bunches for the mill. Wash yourself and your clothes afterwards. And don't lean on one product — rotate to a different chemical group so the fungus can't get used to it.

if bunches keep rotting even after you clear them, the trouble is almost always poor pollination and a damp, crowded canopy — so count and protect the weevils, and open the canopy by pruning dead fronds. Tighten your sanitation to a weekly round, strip every rotten and aborted bunch off the worst palms, and carry it all right out of the field. Fix the pollination and the airflow and the rot has nothing to start on.