Ten common greenhouse tomato problems and how to diagnose them

Many tomato problems look similar from a distance. The useful diagnosis comes from the plant part affected, the age of the tissue, the pattern across the greenhouse and recent climate or irrigation changes. Use this guide to decide what to inspect next, not as a substitute for laboratory confirmation.

Ten symptom patterns

• Upward leaf roll without spotting: review heat, pruning, water stress and root restriction.
• Uniform yellowing on older leaves: check nitrogen supply, roots and irrigation.
• Purple older leaves and slow growth: check cold roots, pH and phosphorus availability; root-zone temperature below roughly 15–16°C limits phosphorus uptake even when soil phosphorus is adequate.
• Yellow upper spots with olive growth underneath: investigate tomato leaf mold and humidity.
• Lower-leaf spots with concentric rings: investigate early blight and sanitation.
• White or bleached fruit surface: check direct sun exposure and high fruit temperature; surface temperatures above roughly 40–42°C in direct sun typically cause sunscald bleaching.
• Dark lesion at the blossom end: review calcium transport, root health and irrigation uniformity; risk rises sharply when substrate moisture swings more than 20–30% between irrigation events.
• Radial or concentric fruit cracking: check rapid water uptake and irrigation fluctuations.
• Uneven or yellow-shoulder ripening: review heat, canopy cover, potassium balance and light.
• Flowers dropping without fruit set: review temperature, humidity, pollination and plant balance.

Use the greenhouse pattern

A problem aligned with one valve, pipe or bed suggests irrigation or dosing. Edge rows may show heat, light or ventilation effects. Random expanding spots point more strongly toward a biological agent. Map the first symptoms rather than relying on the worst plant.

Inspect roots and measure feed and drain pH, EC and volume. Root damage, poor aeration and salt accumulation can create several above-ground symptoms at the same time.

Correct the cause in the right order

Stabilise irrigation, root-zone oxygen and climate before making large nutrient changes. For suspected disease, reduce leaf wetness, separate tools and submit a sample. Avoid removing too much canopy: exposed fruit can develop sunscald and uneven ripening.

For blossom-end rot, adding calcium alone may not solve the problem if roots alternate between wet and dry or EC is excessive. For cracking, aim for steadier water availability rather than restricting water after damage appears.

Local adaptation: the United States

For U.S. farms, keep both °F and °C in the operating log, use a local laboratory for water and tissue tests, and follow the label and state rules for every crop-protection product.

Diagnostic checklist

1. Map symptoms by bed, valve and greenhouse zone.
2. Inspect roots, young leaves, old leaves and both leaf surfaces.
3. Review the previous seven days of climate and irrigation.
4. Measure feed and drain pH, EC and volume.
5. Confirm contagious or persistent problems with a laboratory.

The best tomato diagnosis links a visible symptom to measurements and production history. That approach prevents one correction from creating a second problem.

Important: Use Gros.farm to keep sensor readings, observations, photos and corrective actions in one production log. It supports decisions but does not replace local controllers, safety systems or laboratory diagnosis.

Sources and further reading

• University of Minnesota Extension: Tomato Disorders
• University of Minnesota Extension: Tomato Leaf Mold
• UMass Extension: Tomato Physiological Ripening Disorders