Potato late blight: spot it early, act before it spreads

4 November 2026 · 2 min read · Krishoker Thikana desk

Late blight is the most feared disease of potato in Bangladesh. It comes with the cold, foggy, humid days of December and January, and in the right weather it can spread across a whole field, and the fields next to it, within a few days. Tomato and eggplant can be hit too.

Scientists at the Tuber Crop Research Centre of the Bangladesh Agricultural Research Institute (BARI) advise acting early: protective sprays at about 7-day intervals once the risky weather sets in, rather than waiting until the disease is visible.

Warning signs

• Pale green or dark, water-soaked patches on the leaves, often starting at the tips and edges.
• The patches quickly turn brown-black and spread; on damp mornings a thin white growth can be seen on the underside of the leaf.
• Black or brown streaks on the stems; plants collapse as if burnt.
• A rotten smell from the field in bad cases. Tubers can get brown, sunken patches and rot in storage.

Prevention

• Plant healthy, certified seed potato. Do not use tubers from a field that had blight.
• Watch the weather. When fog and drizzle last for two or three days, that is blight weather.
• Start protective fungicide sprays before symptoms appear, as advised by your agriculture officer. Use only recommended products at the dose on the label, wear a mask and gloves, and keep children and animals away.
• Avoid irrigating in the evening and avoid too much nitrogen fertiliser; both keep the crop leafy and wet.

If you see it in your field

1. Act the same day. Pull out and bury or burn badly affected plants; do not leave them in the field or throw them in a canal.
2. Call the Krishi Call Centre at 16123 or your Sub-Assistant Agriculture Officer and ask which curative fungicide to use and how often.
3. Tell your neighbours. Blight spores travel with the wind, so treating one field alone is not enough.
4. At harvest, cut and remove the haulm (leaves and stems) a week or so before digging, and do not store damaged or rotten tubers with healthy ones.

Spray safely

Fungicides are chemicals. Buy them only from licensed dealers, check the expiry date, never mix products on guesswork and never spray against the wind. Wash hands and face after spraying, and keep to the waiting period on the label before harvest.

The Research & varieties section of this site links to BARI and other research institutes; the Government services section lists the Department of Agricultural Extension.