Narrow Brown Leaf Spot: How to Spot It and Stop It in Palay

Most seasons it is a minor problem. Bad outbreaks have been seen only now and then, and most of the time it costs farmers little. Even so, a bad attack can lower the market value of the grain and the milling recovery, so it pays to know the signs. Our guide to rice diseases shows where it fits among the other leaf problems.

How to Identify Narrow Brown Leaf Spot

Look at the older leaves and the flag leaf from heading. The lesions are narrow, light to dark brown, and they run straight along the veins. Each one is about 2 to 10 millimeters long and 1 to 1.5 millimeters wide. On a very susceptible variety they grow wider and join into larger dead areas. On the leaf sheath, brown and yellowish patches make a net pattern, called net blotch.

• Thin, straight brown lines run parallel to the veins on the leaf and the upper sheath.
• Each line is short, about 2 to 10 millimeters long, and light to dark brown.
• On a susceptible variety the lines widen and join into bigger dead patches with a pale center.
• The leaf sheath shows a brown and yellowish net pattern.
• Leaves and sheaths die early, and the grain may ripen early in a bad attack.

How Narrow Brown Leaf Spot Hurts Your Palay

Severe narrow brown spot kills leaves and sheaths early, makes the grain ripen too soon, and in a severe case can cause the plants to lodge. It also cuts the price the grain fetches and how much rice comes out of the mill. Bad outbreaks that cut the harvest are rare, so for most farmers the loss is small. Where the disease is bad, the main loss is in grain quality.

The disease is linked to soils short of potassium and appears late in the crop, from heading. So the signs on your leaves can also warn you about the soil. Our guide to fertilizer for rice explains how potash and nitrogen fit together. We found no official action threshold for spraying in the Philippines.

How to Control Narrow Brown Leaf Spot

1. Test or review your soil, and correct a potassium shortage with potash. The disease is linked to potassium deficient soils.
2. Use certified, disease free seed paddy, and choose varieties that show less of the disease. Resistant varieties show much lower damage in trials.
3. Follow the recommended nitrogen rate, or use the leaf color chart so you do not overfeed the crop.
4. Keep the field free of weeds, since weeds hold the disease and crowd the crop.
5. Add organic fertilizer to build up the soil, so the crop stays healthy to the end.
6. After harvest, do not return diseased straw to the soil, and clear stubble from the field.

When a Spray Makes Sense

A fungicide is rarely needed, because the disease is usually minor. Trials in the United States found that a spray at panicle initiation or early boot worked well on a susceptible variety, but we found no Philippine recommendation. Check with your local agriculture office first and follow the product label.

Keep It Out Next Season

• Test the soil and fix a potassium shortage with potash. The disease follows potassium poor soils.
• Use certified seed of a variety that shows less of the disease.
• Follow the recommended nitrogen rate, or the leaf color chart, so you do not overfeed.
• Keep weeds down in the field and on the bunds, and add organic matter to build the soil.
• Plant at the best time for your area, and clear diseased straw and stubble after harvest.

Not Sure What You Are Seeing?

Take a clear photo of the spots or the damage up close, then the whole plant, then ask Anee, the smart farm technician in anee.io, in Tagalog or English. Anee tells you what it most likely is and what to do at the age of your crop. You can also put your scouting days on the cropping calendar, so the team knows when to walk the field.

Questions Farmers Ask About Narrow Brown Leaf Spot