Taro leaf blight
The disease that decides an arbi crop — small water-soaked spots on the leaves that can strip a whole field within days of warm, humid weather.
- Pathogen
- Oomycete (P. colocasiae)
- Spreads by
- Rain-splashed spores; infected cormels
- Favoured by
- Warm (20–28°C), humid, wet-leaf weather
- Main risk
- 25–50% yield loss; whole-canopy defoliation in days
Overview
Taro leaf blight, caused by the fungus-like oomycete Phytophthora colocasiae, is the single most damaging disease of taro (arbi/colocasia) worldwide. It thrives in exactly the warm (20–28°C), humid weather with prolonged leaf wetness that most of India's taro belt gets during the monsoon, and where it is not managed it can cause 25–50% yield loss in a single season.
It starts as small, water-soaked spots on the leaves, which rapidly enlarge into big brown-to-purple lesions, often with faint concentric rings and drops of yellowish fluid on the underside in humid conditions. Badly affected leaves collapse, and the whole leaf canopy of a field can be stripped within days once the disease establishes. In severe, prolonged outbreaks the petioles and even the corm itself can rot, cutting straight into the harvestable yield rather than just the foliage.
How to identify it
- Small, water-soaked spots on the leaves that enlarge fast into big brown-to-purple lesions.
- Faint concentric rings within the lesion and, on the underside in humid weather, drops of yellowish fluid.
- Badly affected leaves collapse; the whole canopy can be stripped within days once the disease takes hold.
- In severe or prolonged outbreaks, rot spreading into the petioles and even the corm itself.
What causes it and when
- The oomycete Phytophthora colocasiae, whose spores spread by rain-splash and infect through prolonged leaf wetness.
- Favoured by warm (20–28°C), humid weather — exactly the conditions of most of India's taro-growing belt during the monsoon.
- Also carried over on and inside infected cormels used as planting material, seeding a new field with the disease before a single spore arrives by air.
- Spreads extremely fast once established — a field's canopy can be stripped within days in favourable weather.
Cultural & organic control
- Grow a tolerant variety — Sree Hira, Sree Pallavi and others show useful field tolerance to this disease.
- Propagate cormels only from mother plants that never showed blight symptoms, even in a different part of the same field.
- Space plants for good airflow and avoid overhead irrigation late in the day, which prolongs leaf wetness.
- Remove and destroy heavily infected leaves as soon as they are seen to slow spread within the field.
Chemical control
- Apply a recommended copper-based or systemic fungicide at the first water-soaked spots, before the disease spreads through the canopy.
- Repeat through humid monsoon spells, since the disease can re-establish quickly in favourable weather.
- Treat cormels with a fungicide dip before planting to cut down inoculum carried on the planting material itself.
- Follow the label and pre-harvest interval, and confirm the current recommended product with your local KVK.
Prevent it coming back
- Base the next crop on a tolerant variety and cormels from mother plants that stayed clean all season.
- Rotate away from arbi on land with a history of severe blight where practical.
- Start scouting as soon as the monsoon's first humid spell arrives, rather than waiting for visible spread.
Crops most at risk
Where this problem is called out in our crop guides — open a crop for the full package of practices.
Frequently asked questions
My arbi leaves have brown-purple patches spreading fast in the monsoon. What is it?
That is almost certainly taro leaf blight, the most damaging disease of taro worldwide. It thrives in warm, humid weather and can strip a field of leaves within days once established. Remove the worst-affected leaves, spray a recommended copper-based or systemic fungicide now, and for the next crop choose a tolerant variety and propagate only from mother plants that never showed the disease.
Can I stop taro leaf blight just by spraying after I see it?
Spraying helps once symptoms appear, but the disease spreads so fast in humid weather that acting only after visible spread often means real yield is already lost. The stronger approach combines a tolerant variety, clean cormels from symptom-free mother plants, good plant spacing for airflow, and fungicide applied at the very first water-soaked spots rather than after the canopy is already affected.
Can infected cormels spread this disease even without wet weather?
Yes — the fungus carries over on and inside infected cormels used as planting material, so a bad batch can seed an entire new field with blight before the season's first humid spell even arrives. This is why propagating only from mother plants that stayed clean all season matters as much as weather-based spraying.
Symptoms and control measures follow ICAR, KVK and state agricultural-university package-of-practices; any named chemical is a registered use. Always read the product label and confirm the dose for your crop and zone. editorial policy.