Why Are My Corn Leaves Turning Yellow?

Corn is a heavy feeder and its leaves are a reliable indicator of what is happening below ground. Uniform yellowing spreading from the leaf tip backward, starting on older lower leaves, is a textbook nitrogen deficiency signal. But cold soil, waterlogging and several diseases produce yellow leaves too, and treating the wrong cause wastes time and money. Reading the pattern — which leaves, which part of the leaf, which direction the yellowing moves — gives you the diagnosis before you open a bag of fertiliser.

Nitrogen deficiency — the V-shaped yellow stripe

The most recognisable nitrogen deficiency symptom on corn is a bright yellow stripe running from the leaf tip down the midrib, forming a V-shape, while the leaf edges stay greener for longer. It starts on the lowest, oldest leaves and moves progressively up the plant. Corn is a heavy nitrogen consumer and quickly exhausts even well-prepared soil in wet weather when nitrogen leaches rapidly. Apply a high-nitrogen liquid feed at half the recommended rate and repeat every two weeks through the growing season. Work granular nitrogen into the soil before sowing on light, free-draining ground.

Cold soil limiting nutrient uptake

Corn planted into soil below 15°C cannot take up nutrients efficiently even when they are present in adequate quantities. The roots simply cannot function at low temperatures. The plant yellows overall, grows slowly and looks starved despite being in fertile soil. This corrects itself as the soil warms — resist the urge to overfeed a cold plant, which can cause salt stress once the soil warms and absorption resumes. Warm the bed with black polythene for a week before sowing if your season is short and cool.

Waterlogging and root oxygen shortage

Corn in waterlogged soil develops yellow leaves from the bottom up as the roots suffocate and fail to absorb nutrients. Unlike nitrogen deficiency, the yellowing is more general and less stripe-patterned. The soil will feel cold and wet and may smell stale. Improve drainage, stop watering, and wait for conditions to dry. Corn grown in raised beds or on ridged soil avoids this problem in wet seasons.

Stewart's wilt and other diseases

Stewart's wilt, caused by a bacterial pathogen spread by corn flea beetles, causes pale-green to yellow streaking on younger leaves, often with a wavy, irregular margin rather than a clean V-shape. It is more common in warm winters that allow large flea beetle populations. There is no cure for infected plants — remove and destroy them. Resistant varieties are the main management tool. Fusarium and other root rots also cause yellowing when they compromise water and nutrient uptake at the root level.