Turmeric leaf blotch

many small blotches scattered over the leaves — starting as tiny dirty-yellow specks, then turning reddish-brown. They show on both sides of the leaf, and on the underside they often look a dull, muddy yellow. There are usually lots of them at once, not just one or two.

the little blotches multiply and run together, so the leaf takes on a dirty, rusty, reddish-brown look all over — as if it has been splashed with mud and left to dry. Badly hit leaves dry from the edges and tips inward, and in a wet year the plant can look scorched and ragged.

it shows up on the leaves during the leafy and bulking months, worst in cool, wet, cloudy weather and on crowded, shaded, poorly-drained beds where the leaves stay wet a long time. It attacks the leaves only — it does not rot the rhizome the way rhizome rot does.

with turmeric leaf spot, which makes fewer, larger, oval brown spots with a pale grey or whitish centre ringed in yellow (sometimes with tiny black dots in the middle). Leaf blotch makes many more, smaller blotches with no grey centre and gives the whole plant that dirty rusty wash. Don't confuse it with plain sun-scorch or hunger (nutrient shortage) either — those yellow the whole leaf or its edges evenly, they don't pepper it with separate brown blotches.

through the leafy-growth and bulking months (the development and mid-season stages), when the plant is carrying a full head of leaves. Step up your checks the moment the weather turns cool, wet, cloudy or foggy, or after rain and heavy dew (about 15-25 degrees C) — that damp, dull weather is exactly when the blotches explode.

once a week, walk a big "W" shape so you cross all four corners and the middle — not just the row nearest the path. Make about 10 stops along the way, and look hardest at the crowded, shaded, low-lying beds where the leaves dry slowest.

look closely at about 10 clumps, and turn the leaves over to check both sides. Look at the younger, newer leaves as well as the old ones, hunting for the small dirty-yellow to brown blotches.

don't wait for the field to turn rusty. Act as soon as the first 1 or 2 plants in a patch show fresh, spreading blotches — that handful of speckled plants is your trigger, because in cool wet weather the disease jumps from leaf to leaf fast. If cool, cloudy, rainy weather has settled in and blotches are showing, treat early, while the leaves are still mostly green.

the moment you find the first speckled leaves, pick off the worst-blotched leaves and carry them right off the plot — burn or bury them, don't drop them on the bed or the compost. Do this on a dry day so you don't spread wet spores by hand. Removing that first source slows the disease while you decide whether you need to spray.

if the weather stays cool and wet and the blotches keep spreading despite the steps above, use a protectant (contact) fungicide such as mancozeb, copper oxychloride, or a copper (Bordeaux) mixture. "Protectant" means it coats the leaf and stops new spores taking hold — it shields healthy leaf but cannot heal a blotch already there, so it must go on at the very first spots and be re-sprayed every 2-3 weeks through the wet spell and after rain washes it off. Cover both sides of the leaves.

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 food you'll eat soon, off drinking water and rivers, and away from children and bees. Respect the pre-harvest interval — the number of days the label says you must wait between the last spray and harvesting. Wash yourself and your clothes afterwards, and follow the label.

don't lean on one product forever — rotate to a different chemical group each time so the fungus can't get used to it. Lean on the prevention and airy-crop steps as the backbone, and use the spray only as the backup when wet weather forces your hand.

if blotch is climbing through the crop, tighten the spray schedule to the wet-weather interval, keep stripping and removing the worst leaves, and improve the airflow and drainage on the sickest beds. The aim now is to keep as much green leaf alive as you can through bulking — every leaf you save is weight kept in the rhizome. At harvest, clear and destroy all the blotched trash and keep only clean, unblotched rhizomes back for next season's seed.