Lettuce

Peronospora spp.

A fungal-like disease that causes yellowing on upper leaf surfaces with grey or purple fuzzy growth underneath. Favours cool, damp, humid conditions and spreads rapidly in still, wet weather. Unlike powdery mildew, it requires wet or very humid conditions to spread.

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.

Bolting is the premature production of a flowering stem, triggered by temperature stress, day length, or drought. Once a plant bolts, leaf and root quality declines rapidly and the crop becomes bitter or tough. It is particularly common in early sowings exposed to cold followed by warmth.

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.

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.

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.

Shell-bearing molluscs that feed on foliage and young plants, leaving similar damage to slugs. They are more active in mild, damp conditions and tend to shelter in visible daytime hiding spots such as walls, pots, and debris.

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.