Identify cause of wheat turning yellow, take timely measures, say experts

Wheat sowing has been done and wheat turning yellow has nowadays become a common problem for farmers.

Many times, the farmers do not know the exact cause and spray pesticides, assuming it to be a disease. It increases costs and can also harm the crop.

“In reality, wheat turns yellow due to several reasons — nutrient deficiency, excess or shortage of water, poor soil health, insect attack and diseases such as yellow rust. Identifying the real cause and taking timely steps can prevent unnecessary expenses and ensure higher yields,” said Prabhjit Kaur, Assistant Professor (Agronomy), PAU.

Weather and water conditions are often responsible for wheat turning yellowish. Sudden drop in temperature or persistent fog in winter can change the leaf colour, though it usually corrects itself in a few days. Farmers should ensure timely irrigation to maintain soil moisture. Excess water after irrigation or rainfall could deprive roots of oxygen, leading to yellowing and drying of leaves, especially in heavy soils, she said.

To avoid this, farmers should make eight plots per acre in heavy soils and 16 plots per acre in light soils and drain stagnant water quickly. Poor-quality tube well water, especially saline water, could also cause yellowing. Water should be tested before use and gypsum should be applied, if needed. Mixing saline water with good-quality water can minimise damage, Kaur said.

Nutrient deficiencies were another major cause. Nitrogen deficiency was common, appearing first in older leaves that turn yellow from tip downwards. It could be corrected with urea as per soil test recommendations, with 25 per cent extra nitrogen in saline or alkaline soils. Zinc deficiency slows growth, stunts plants and causes central leaves to turn yellow with white bands. Preventive measures include applying 25 kg zinc sulphate per acre at sowing or spraying 0.5 per cent zinc sulphate solution during growth, says Harwinder Singh Buttar from the Department of Plant Pathology.

Manganese deficiency shows as yellowing between veins of leaves, often with grey or pinkish streaks, and is common in light soils and wheat-rice systems. Spraying manganese sulphate after first irrigation helps. Sulphur deficiency, common in sandy soils, causes yellowing of new leaves while older ones remain green. Applying gypsum or bentonite sulphur per acre can manage the problem but gypsum should always be applied after irrigation.

Pests and diseases also contribute significantly, Buttar said.

Termite attack after sowing leads to yellowing, drying and easy pulling of seedlings, especially in sandy soils. Seed treatment before sowing or application of fipronil or chlorpyriphos mixed with moist sand could prevent damage. Pink stem borer larvae bore into stems, causing yellowing and dead hearts, adds Sanjeev Kumar Kataria, another expert from the PAU.

Farmers should avoid October sowing in infested fields, irrigate during daytime and apply recommended insecticides if infestation is high. Nematodes cause stunted, yellow plants with root galls, reducing yield. Management includes ploughing fields in May-June, avoiding wheat in infested areas, and applying furadan at sowing. Yellow rust disease was another major threat, producing yellow powdery pustules on leaves that spread in cool, moist conditions. Preventive measures include sowing resistant varieties, monitoring from mid-December and spraying fungicides such as captan hexaconazole, tebuconazole, trifloxystrobin Tebuconazole, Azoxystrobin combinations, or Propiconazole. Sprays should be applied only on affected patches and repeated as needed, Kataria said.

Experts emphasise that farmers should not rush to spray pesticides without identifying the cause of yellowing. Timely irrigation, soil testing, balanced nutrient management and vigilant monitoring of pests and diseases were key to keeping wheat fields green and healthy.