Boll rot

on a green, developing boll you'll see a small water-soaked spot — a dark, wet, greasy-looking patch that feels soft, not firm like healthy boll wall. It often sits right beside an insect sting or hole, or low down where a shaded boll stays damp after rain.

the spot turns brown, then black, and grows a fuzzy surface mould — this can be pink, black, grey or sooty depending on which fungus took hold. Whole bolls can go black, hard and shrivelled ('mummified') and just hang on the plant instead of opening.

a rotted boll won't open and fluff. The segments (called locks) stay hard and stuck shut — farmers call this 'hardlock'. Prise or cut one open and the cotton inside is stained yellow-brown-black, matted and rotten, not clean white fluff. That stained lint is worthless.

it starts on the lower, inner bolls in the thick, shaded part of the plant that stays wet the longest, and mostly on developing (green) and maturing bolls during warm, humid, rainy spells.

(1) a healthy boll opening — that one dries pale tan and splits cleanly to white fluff; (2) plain bollworm damage — a neat round hole with a caterpillar or dry droppings inside but no mould and no wet rot (though that hole is often the very doorway the rot uses next); (3) weather-greyed lint on bolls that already opened normally — dull and discoloured but dry, not slimy or mouldy.

start once bolls begin to form and set, and keep going through boll development and boll-fill (the mid-season and late season) right up to harvest. Step up your checks after every rain and during warm, muggy, humid weather (around 24-32°C) — that wet, close air is exactly when the rot takes off.

cross the field in a big 'W' so you cover all four corners and the middle, not just the outer rows by the path. Make about 5 stops along the W.

The rot hides on the lower, inner bolls deep in the canopy, so bend down and part the plants with your hands — don't just glance at the top, outer bolls. At each stop check about 10 plants.

water-soaked spots, surface mould, and bolls that stay hard and won't open. Check every boll that has an insect hole, and cut open two or three suspect bolls to see if the lint inside is stained and rotten.

even 1-2 spoiled or mouldy bolls in every 10 plants low in the canopy during wet weather is your signal to act now — especially if those bolls also carry insect holes. Don't wait for it to climb up and out through the crop; in a dense, wet canopy a small start becomes a big loss fast.

Give plants correct, not-too-tight spacing, and go easy on nitrogen fertiliser: too much makes soft, leafy 'rank' growth (thick, lush growth) that traps damp, still air around the bolls. Sun and moving air dry bolls quickly and starve the rot of the wetness it needs.

Bollworms and sucking bugs punch the wounds the rot creeps in through, so controlling those insects is really controlling boll rot. Scout for these pests and their entry holes alongside your rot checks.

Harvest open, sound bolls as soon as they're ready — don't leave good lint hanging in wet weather to spoil and stain. Where you can safely reach them, pick off and carry away the badly rotted, mouldy bolls so they stop shedding spores onto the healthy ones.

Spraying a fungicide straight onto bolls rarely pays on cotton. What can help is a pyrethroid insecticide (a common contact insect spray — 'contact' means it kills the insects it lands on but does not travel inside the plant) used against the bollworms and sucking bugs, to stop the wounds before they start. Only spray when those insects are actually present in numbers — never on a fixed calendar.

Cover your skin, eyes, nose and mouth; spray in the cool of the morning or evening with the wind at your back; keep it well off food, drinking water, children, animals and bees; and wash yourself and your clothes afterwards. Respect the pre-harvest interval (the set number of days you must wait between the last spray and picking, printed on the label). And to stop the pests building resistance (surviving the spray until it stops working), rotate to a different chemical group each time rather than using pyrethroids over and over.

in a long wet spell, open the canopy harder (thin or defoliate for airflow) and pick early and often to rescue every sound boll before it spoils. Bolls that are already black, hard and mouldy are lost — cut your losses: leave them, save the clean bolls, and set up next season to win — wider spacing, less nitrogen, and tighter insect control right from the start.