Turmeric leaf spot

small brown to reddish-brown spots on the leaves, each ringed by a yellow halo (a pale yellow edge, like a bruise around the spot). This is the earliest and clearest sign.

the spots grow and join into larger, irregular blotches with pale, dried-out grey centres. Look closely at those centres and you may see tiny black dots — these are the fungus's seed-cases. In a heavy attack the leaf dries, browns and tatters at the tips and edges as if scorched.

worst in warm, humid, rainy weather (about 21-30°C) when leaves stay wet for hours, and in crowded clumps with poor airflow. Ginger in your garden gets the same disease, so check it too.

sun-scorch or fertiliser burn (browns the leaf edges evenly, with no round spots and no yellow halo) or ordinary old-age yellowing of the lowest leaves (a whole leaf yellows slowly, no brown spots with haloes). True leaf spot gives you distinct round spots with yellow rings that multiply and merge.

walk your turmeric once a week during the rains, from when the plants are pushing out new leaves and building the clump right through the wet months — this is when the leaves are most at risk and the rhizomes are bulking.

cross the plot in a big "W" shape so you cover all four corners and the middle, not just the row by the path where you always look.

stop at about 10 clumps along the W. At each stop, turn over and check several leaves — both the lower older leaves and the fresh upper ones — for brown spots with yellow haloes.

the fungus is always around at a low level, so a stray spot or two is normal. Act once you find fresh, spreading spots on more than a couple of leaves in a clump — roughly 1 in 5 leaves spotted — across several clumps during the rains, and act sooner on a variety you know catches it easily. Fresh, growing spots with bright haloes mean it is active now; old dry grey blotches with no new spots are a past attack.

as soon as the first spotted leaves appear, pick them off and burn them (don't drop them in the field or the compost, and don't move from a sick clump to a healthy one carrying spores on your hands or tools). Opening up crowded clumps to let air in slows the spread for free.

if spots keep multiplying in wet weather past your action point, use a copper-based fungicide. Copper is a protectant — meaning it forms a shield on the leaf to stop new infections but does not cure spots already there — so spray it at the very first spots and repeat during long wet spells to keep new leaves covered. Cover the plant well, including under the leaves.

cover your skin, eyes, nose and mouth; spray in the cool of the morning or evening with the wind behind your back so the mist blows away from you; keep it off food, drinking water, children and bees; respect the pre-harvest interval (the number of days you must wait between the last spray and harvest, printed on the label); and wash yourself, your clothes and the sprayer afterwards. Don't lean on copper alone every time — keep up the clean-planting, spacing and sanitation so the disease never gets the upper hand.

if a heavy attack strips most of the leaves late in the season, don't waste money spraying dying foliage — let the crop finish, then harvest the rhizomes, clear and burn every leaf and stalk off the plot, and choose only clean, firm rhizomes as next year's seed. Move next season's turmeric to fresh ground to start the new crop ahead of the disease.