Tomato Plant White Spots on Leaves: Causes and Fixes

Tomato powdery mildew in the UK is caused by Oidiopsis taurica (also known as Leveillula taurica), a fungal plant disease that differs from most garden powdery mildews. It can infect through stomata as well as on the surface, and it thrives in warm, dry conditions with cool nights — conditions common inside UK greenhouses in late summer. It appears first as pale yellow patches on the upper leaf surface, which then develop a white or grey powdery spore coating. Infected leaves eventually turn yellow and fall. The University of Connecticut Extension IPM team confirms this species is particularly problematic for indoor tomatoes. The RHS lists this on its tomato leaf problems advice page.

Stop it coming back:Infected leaves do not recover, but the plant can continue cropping if conditions are improved. Focus on ventilation, consistent watering and removing infected material as the main prevention strategy.

stop watering to combat powdery mildew — dry roots are a predisposing factor; maintain consistent root moisture.

Septoria leaf spot is one of the most widespread tomato diseases in the UK, affecting outdoor and tunnel-grown plants alike. It is caused by the fungus Septoria lycopersici and appears as small, circular spots — typically 3–6mm across — with a grey or white centre and a dark brown to black border. Tiny dark specks (the fungal fruiting bodies, called pycnidia) are often visible in the white centre under a hand lens. The disease starts on the lowest, oldest leaves and works upward through the canopy. It is strongly associated with wet or humid weather, overhead irrigation, and poor airflow. Seed Parade UK lists it as one of the primary tomato leaf diseases.

Stop it coming back:Infected leaves will not recover. Focus on preventing spread: remove affected material promptly, improve airflow, and avoid wetting the foliage. Outdoor crops are more exposed — staking and training to improve airflow is particularly helpful.

compost infected tomato leaves or stems — Septoria can persist in compost heaps that do not reach sufficient temperatures to kill the spores.

Sun scorch on tomato leaves appears as pale, bleached or papery white patches — typically on the side of the leaf facing direct sun. It is not infectious. In UK greenhouses, scorch happens most often when ventilation fails, temperatures spike above 30°C inside, and plants cannot cool themselves adequately. Plants moved suddenly from a shaded indoor position to full outdoor sun may also show scorch on new leaves that have not hardened in direct sunlight. The RHS tomato guidance notes that whitewash on greenhouse glass can be used to reduce extreme summer scorch.

Stop it coming back:Sun-scorched tissue does not recover, but new growth in better conditions will be normal. Harden off plants gradually when moving them outdoors — a week of dappled shade before full sun exposure prevents most scorch.

assume sun scorch is a disease and apply fungicide or copper spray — it is a physical injury, not an infection.

Oedema (also spelled edema) on tomato leaves appears as raised, corky or blistered bumps, typically on the undersides of leaves, which may appear whitish or pale. It occurs when the plant absorbs water faster than it can transpire — most commonly in UK greenhouses in cool, humid conditions with high soil moisture and low light. The internal cells rupture under pressure, producing the characteristic bumps. The RHS has a dedicated page on oedema confirming it is a physiological disorder rather than a disease, so no pest control is appropriate. Once formed, the bumps do not disappear, but new growth in corrected conditions should be clean.

treat oedema with insecticides or fungicides — it is caused by excess water uptake, not by any pathogen or pest.

Tomato leaf mould is caused by the fungus Fulvia fulva (formerly Cladosporium fulvum) and is primarily a disease of greenhouse and tunnel-grown tomatoes in the UK. The RHS has a specific page dedicated to it. Initial symptoms are pale yellow or green spots with unclear edges on the upper leaf surface — these can look like whitish patches. The diagnostic feature is what appears on the underside: an olive-green or brownish velvety growth corresponding to each upper spot. In severe cases, infected leaves curl, yellow and fall prematurely. The disease thrives in humid, poorly ventilated greenhouses with temperatures of 20–25°C.

leave affected plants in a poorly ventilated greenhouse — leaf mould spreads quickly under those conditions and can rapidly defoliate a crop.

Irregular watering, salt build-up from heavy feeding, or very high or low pH can occasionally cause scattered pale spots or tan areas on older tomato leaves that do not match the pattern of any fungal disease. These are physiological rather than infectious. They may be associated with blossom end rot on fruits in the same plant — a sign that calcium delivery through the plant is compromised by erratic water supply. The RHS confirms that mineral deficiency spotting in tomatoes is usually secondary to a watering or root problem.

apply foliar calcium or magnesium sprays as a first response — most calcium-related leaf issues in tomatoes trace back to water delivery problems, not nutrient absence in the soil.