Maize ear rot

is usually at the tip of the cob or at any spot an insect or bird has bitten: peel back the husk and you see a felt-like mould growing over the kernels and in the gaps between them, and the grain underneath is dull, shrunken and light as chaff instead of hard and full.

to know which mould you have: soft pink-to-reddish webbing streaking up from the tip or from wounds is Fusarium; a powdery blue-green or olive dust (often near the tip, worse in dry heat) is Aspergillus — the one most linked to the worst poison, aflatoxin; a greyish-white to brown rot that starts at the base of the cob and makes the whole ear rot and stick together is Stenocarpella (Diplodia).

a bad cob is light and springy, the husk may be bleached and glued to the kernels, and mould can grow right through to the shank so the ear droops or the kernels are chalky and criss-crossed with white threads.

with normal ripening. Healthy drying husks go papery-brown on the outside while the kernels stay hard, full and bright — that is fine. Ear rot is mould on the kernels themselves, soft rotten grain, and off colours (pink, blue-green, grey). A few insect-chewed kernels with no mould are just insect damage, not rot — but they are the open door the mould walks through.

start once the crop is late in the season — from silking, through the doughy grain-fill stage, and right up to harvest. This is the only window ear rot cares about: wet, humid weather over the silks plus any cob wounds is exactly what the mould waits for.

walk a big "W" across the field so you cross all four corners and the middle, not just the row by the path. Make about 10 stops along the way.

at each stop pick a cob and peel the husk halfway down on 1 plant — about 10 cobs in all. Look hard at the tip and at any insect or bird wounds, because that is where the mould starts. Check extra cobs on any plant a stalk borer or earworm has attacked, and on lodged (fallen) plants.

there is no spray, so the trigger is different — the moment you find mould on even one cob near maturity, treat the whole field as at risk and get ready to harvest and dry fast. If you peel 10 cobs and 1 or more shows mould, do not leave the crop standing to "finish" in the field — every extra wet day multiplies the mould and the poison.

a spell of warm, wet, humid weather (roughly 18–30°C) from silking onward, or a crop you cannot harvest on time, both push the risk up sharply — scout more often when either is true.

— do not waste money on one, and never try to "clean" mouldy grain to sell or eat, because the mycotoxins (the hidden poison) stay in the grain even after the mould is brushed off. If any spraying is done, it is only the insect control above — and then follow full safety: cover your skin, eyes, nose and mouth, spray in the cool of the day with the wind at your back, keep it away from food, water, children and bees, respect the waiting period before harvest (the pre-harvest interval — the minimum days between spraying and picking), and wash yourself and your clothes afterwards.

if wet weather sets in and rot is climbing through the field, harvest early rather than lose more — a slightly early, clean crop beats a fuller, mouldy one. Cut your losses on the badly rotten cobs: separate them out, keep them completely out of your family's food and your animals' feed, and use only for non-food purposes or discard them. Save and store only the clean, well-dried grain.