Tomato

Phytophthora infestans

A fast-moving water mould that can devastate tomato and potato crops within days under warm, humid conditions. One of the most serious disease risks in the kitchen garden.

Alternaria solani

A common fungal disease that typically appears on older, lower leaves first, causing distinctive concentric ring-patterned lesions. Less aggressive than late blight but can significantly reduce vigour if unchecked.

Plants are drooping or losing vigour. Most commonly caused by water stress but can also indicate root damage, vascular disease, or heat scorch. Identifying the cause quickly is important as some causes are serious.

Seeds are emerging unevenly or not at all. Usually caused by soil temperature being too low, seeds sown too deep, poor seed-to-soil contact, or old seed stock.

Pythium spp. / Phytophthora spp.

Young seedlings collapse at or just below soil level, caused by fungal pathogens that thrive in overwatered, poorly ventilated growing conditions. Can spread rapidly through a seed tray.

Leaves are turning yellow, which can indicate a range of problems including nutrient deficiency, overwatering, disease, or natural senescence. Identifying whether the pattern is upper or lower leaves, whole leaves or between veins, is key to diagnosis.

Plants are significantly smaller or slower to develop than expected. May be caused by poor soil, nutrient deficiency, root restriction, compaction, pest damage to roots, or disease.

Roots are decaying, usually caused by excess moisture, poor drainage, or soil-borne pathogens. Affected plants cannot take up water or nutrients effectively and typically decline rapidly.

Botrytis cinerea

Grey mould is an extremely common fungal disease that thrives in cool, damp, still conditions. It can affect almost any soft plant tissue - flowers, developing fruit, leaves, and stems. On strawberry it is one of the most significant causes of fruit loss.

A calcium deficiency disorder causing dark, sunken, leathery patches at the blossom end of developing fruit. The root cause is almost always irregular watering rather than calcium-poor soil - drought stress prevents calcium uptake even when soil levels are adequate.

Small sap-sucking insects that colonise soft new growth, leaf undersides, and growing tips. Most species reproduce rapidly and colonies can establish quickly in spring and early summer. Also vectors of several plant viruses.

Trialeurodes vaporariorum

Tiny white-winged insects that cluster on leaf undersides and fly up in clouds when disturbed. Both adults and immature stages suck plant sap, weakening growth and depositing honeydew that encourages sooty mould.

Tetranychus urticae

Tiny mites (barely visible to the naked eye) that feed on the underside of leaves, causing pale stippling and fine webbing. Thrive in hot, dry conditions and reproduce extremely rapidly - populations can explode in a polytunnel or glasshouse during a heat wave.

Soft-bodied molluscs that feed on plant material at soil level, most active at night and in wet conditions. A persistent pressure throughout the growing season, especially damaging to seedlings and young transplants.

General chewing damage from an unidentified pest, leaving holes or missing leaf sections. May be caused by caterpillars, beetles, or other insects. Inspect at dusk to identify the culprit.

General sap-feeding pest activity causing weakened or distorted growth. May be caused by aphids, whitefly, scale insects, or other sucking insects. Inspect leaf undersides and growing tips to identify the pest.