Yellow Tomato Leaves: A Field Guide to Diagnosing the Real Cause

Yellow leaves can mean five very different things — from a simple watering mistake to a virus that ends your season. Here is how to tell them apart in five minutes.

Why this matters

Tomato is one of the highest-value crops a smallholder can grow — and one of the most fragile. A wrong diagnosis of yellow leaves can mean spraying the wrong chemical, losing a week of growth, or in the worst case, losing the whole crop.

Step 1: Where on the plant are the yellow leaves?

• **Lower leaves first:** Usually nitrogen deficiency or natural ageing. Less urgent.
• **Upper / new leaves first:** Iron, sulphur or zinc deficiency, or a virus. More urgent.
• **Random leaves anywhere:** Likely fungal (early blight) or viral (leaf curl).

Step 2: Look at the pattern

• Whole leaf uniformly yellow with green veins → nitrogen.
• Yellow between veins, veins stay green → iron or magnesium.
• Yellow with brown spots that have rings → early blight.
• Yellow + curled upward + plant is stunted → tomato leaf curl virus.

Step 3: Check soil and water

Squeeze a handful of soil 6 inches deep. If it crumbles dry, you are underwatering. If water drips out, you are overwatering — roots may be rotting, which also shows as yellow leaves.

Step 4: What to do (in order)

• Fix watering first. Aim for "moist sponge" — not dry, not wet.
• If nitrogen-deficient: 10g urea per litre of water, sprayed on leaves at evening.
• If iron-deficient: ferrous sulphate 5g/L, weekly for 2 weeks.
• If early blight: copper oxychloride or mancozeb at label dose. Remove affected leaves and burn (don't compost).
• If virus suspected: there is no cure. Remove and destroy affected plants to protect the rest.

When to call for help

If symptoms spread to more than 20% of plants within 3 days, message KhetiGPT on WhatsApp or contact your nearest KVK. Photo-based diagnosis works best with three clear photos — one of the whole plant, one close-up of the worst leaf, and one of the underside.