Taro leaf blight

small dark, water-soaked spots on the leaf — they look wet, greasy and slightly sunken, as if a drop of oily water soaked in. They often start at the leaf edge or tip where dew sits longest.

the spots swell into large brown, dead patches, often with faint rings inside them like a target and a yellow border around the edge. Whole leaves then flop, rot and hang in tatters.

a fine white, downy ring of fuzz on the growing edge of the lesion (that is the mould making its swimming spores in the night's dampness), and sometimes beads of amber (honey-coloured) ooze on the spot. Both dry up and vanish by midday, so check at dawn.

with sun scorch or fertiliser burn (dry, crisp, brown from the tip, no wet edge, no white fuzz, no target rings) or with old insect holes (clean-cut, no rot spreading out from them). Blight is wet-looking, fast-spreading, and grows a white downy ring overnight.

walk your crop at least once a week from the time the plants are putting out big leaves right through mid- and late-season until harvest — and step it up to every 2–3 days whenever the weather turns warm (about 20–28 °C) and wet, with rain, heavy dew or fog. That warm-and-wet spell is when blight explodes.

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

at each stop turn over the newest fully-open leaves and look at leaf edges and tips for fresh water-soaked spots. Go early in the morning while the dew is still on, so you can catch the white downy ring and the amber ooze before they dry.

the threshold is the very first spot. If you find even 1 leaf with a fresh water-soaked lesion — especially in warm wet weather on a variety you know is susceptible — act that same day. Do not wait for a count of many leaves; blight can defoliate the field within days, so the first lesion is your alarm.

as soon as you spot lesions, remove and destroy the infected leaves (rogueing) — carry them out of the field in a bag and burn or bury them; never drop them on the ground or the compost where spores wash back to the crop. Avoid overhead watering, which splashes spores from leaf to leaf; water at the base instead.

if blight keeps coming in a wet spell, protect the crop with a phosphonate fungicide (an oomycete-specific product; copper is a protective alternative). These work best sprayed before heavy infection to shield healthy leaves, on a preventive schedule in wet weather — they cannot raise leaves that are already dead. Safety: cover your skin, eyes, nose and mouth; spray in the cool of the day with the wind at your back; keep it off food, water sources, children and livestock; wash yourself and your clothes afterward; and respect the pre-harvest interval (the minimum number of days the label says you must wait between spraying and harvesting). Resistance: don't lean on one product — rotate between different chemical groups so the germ doesn't learn to survive them.

tighten the loop — spray protectively ahead of each wet spell, rogue harder, and open up the canopy by removing the worst plants so air moves through. If it's already too late and most leaves are dead, cut your losses: harvest the corms early before corm rot sets in, then clean up completely — destroy all crop debris and volunteers, rotate the land away from taro, and start your next crop with a resistant variety and clean setts.