Common pests and diseases on balcony tomatoes

Balcony tomatoes are spared the large-scale disease pressure of a field, but poor airflow and pots packed closely together still bring a predictable handful of problems. Caught early, most of them can be handled without reaching for chemicals — there is no need to wait until a whole plant is dying.

Aphids and whitefly on leaf undersides

Clusters of small insects on new growth and the undersides of leaves are usually aphids or whitefly. They feed on sap and excrete a sticky residue that invites sooty mould. A few can be rubbed off by hand or blasted with a jet of water; larger infestations respond to diluted soap spray applied over three to five consecutive days, avoiding the hottest part of the afternoon.

Leaf spot and early blight

Brown concentric rings on the lower leaves, spreading as the leaf yellows and drops, is typically early blight, and it thrives in long spells of humid, still weather. Pick off and dispose of affected leaves immediately rather than letting them lie on the soil surface, and open up the spacing between plants so foliage is not staying wet for hours at a time.

Suffocated roots

If a plant is visibly stalled and the lower leaves are yellowing with no sign of insects, check the drainage holes at the base of the pot first. Oxygen starvation at the roots looks remarkably like a nutrient deficiency from the outside, and reaching for fertiliser will make it worse rather than better.