Chicory and endive are having a moment in UK kitchen gardens. Radicchio brings bitter depth to autumn salads, witloof (Belgian endive) produces pale forced chicons through winter, and curly or broad-leaved endive fills the hungry gap when summer lettuce has bolted. All four are species of Cichorium, either Cichorium intybus (chicory, radicchio, witloof) or Cichorium endivia (frisee and escarole types), and all share a similar set of problems when leaves start to curl, pucker or distort. This guide walks through the most common causes in roughly the order you should check them.
Lettuce aphid and chicory aphid
The first thing to look for is a dense colony of small insects tucked into the youngest leaves near the growing point. Two species are the most likely culprits on Cichorium crops in the UK: the lettuce aphid (Nasonovia ribisnigri) and the chicory aphid (Uroleucon cichorii). The former is pale yellow-green and tends to cluster deep inside the heart of the plant, making it easy to miss until leaves are already badly distorted. The latter is larger, brownish-red, and more likely to be visible on the outer leaves and stems.
Both species feed by piercing the leaf tissue and extracting sap. As colonies build, the resulting stress causes the young leaves to curl tightly inward and downward, creating a cupped shape that traps further generations of aphids and makes chemical control harder. You will usually notice sticky honeydew on lower leaves first, followed by a sooty mould that colonises the honeydew and turns the foliage grey-black. Heavy infestations cause yellowing, stunted growth, and in severe cases the heart of the plant can be entirely destroyed before it forms a usable head.
Control is straightforward in the early stages. Pick off the worst-affected leaves and drop them into a bucket of soapy water rather than onto the soil. A firm jet of water from a hose will dislodge most of the colony, though it needs repeating every few days. Insecticidal soap or a pyrethrin-based spray applied in the evening, when bees and hoverflies are not foraging, is effective against soft-bodied aphids. Note that some strains of Nasonovia ribisnigri carry resistance to a widely used resistance gene (the Nr gene) present in many lettuce varieties, and a similar dynamic applies to chicory. Rotating varieties and not growing Cichorium crops in the same bed for more than two consecutive years both help limit the local aphid population from building up resistance.
Powdery mildew
If the curling leaves also carry a white or grey powdery coating, particularly on the upper surface, the cause is almost certainly powdery mildew caused by Erysiphe cichoracearum. Unlike most fungal diseases, this one does not need wet conditions to take hold. It spreads by airborne spores during warm, dry, sunny weather, which is precisely why it catches growers off guard in summer and early autumn when chicory and endive are heading up.
The fungus colonises the leaf surface and sends feeding structures into the epidermal cells, disrupting normal growth. Affected leaves curl, pucker and eventually die back from the tips. Young plants are particularly vulnerable. Overcrowding makes the problem significantly worse because it reduces airflow between plants, raises local humidity overnight, and allows spores to spread quickly from plant to plant.
The most reliable cultural fix is spacing. Endive and chicory should sit at least 30 cm apart in each direction; radicchio needs up to 35 cm to head properly. Remove any infected leaves promptly and do not compost them. Potassium bicarbonate sprays alter the pH on the leaf surface and break the fungal colony, and they are approved for organic growing. Sulphur-based fungicides are also effective but should not be used when temperatures are above 30 C. Avoid overhead watering late in the day, as damp foliage overnight encourages spore germination even in otherwise dry conditions.
Lettuce root aphid
A plant that wilts, has curled lower leaves, and fails to respond to watering may have a pest problem underground rather than above it. Lettuce root aphid (Pemphigus bursarius) feeds on the roots of a wide range of salad crops including chicory and endive. It is a greyish-white, waxy, slow-moving insect that congregates around the taproot and lateral roots just below the soil surface. The first visible above-ground signs are wilting on an otherwise moist bed and a general yellowing that starts from the outer leaves inward.
To confirm the diagnosis, carefully lift a suspect plant and look for a white powdery wax at the base of the stem and across the upper root system. This waxy coating is produced by the aphids themselves and is a reliable indicator. Flying adults colonise new sites in midsummer, so beds sown in June or July are especially at risk.
There are no approved pesticide treatments that can be applied at the root zone for home growers in the UK. The practical response is to remove and destroy affected plants immediately, water the surrounding soil thoroughly to disturb remaining insects, and rest that bed from all Asteraceae and Cichorium crops for two years. Yellow sticky traps placed near the soil surface in midsummer catch the winged adults before they lay eggs and give early warning of a building infestation.
Downy mildew and other causes
Downy mildew caused by Bremia lactucae produces pale angular patches on the upper leaf surface with a grey-white downy growth on the underside. It can cause leaf puckering and distortion alongside the discolouration, and it is most active in cool, humid conditions from autumn onward. It is visually distinct from powdery mildew, but both can be present simultaneously on neglected plants in mixed conditions. Remove affected leaves, improve drainage, and avoid any overhead irrigation. Resistant varieties are available and worth seeking out for autumn sowings.
Bolting is worth mentioning as a non-pest cause of leaf distortion. Both chicory and endive are cool-season crops and respond to long days combined with heat by sending up a flowering stem. As this happens, the leaves at the base of the rosette often curl, tighten and become intensely bitter. There is no reversing a bolted plant, but sowing in late July or early August for an autumn harvest, choosing bolt-resistant varieties, and giving plants a position with some afternoon shade in warm summers all reduce the risk significantly. Endive grown in part shade takes longer to develop but is far less prone to bolting and produces more tender leaves.
Prevention
Most problems with Cichorium crops come back to three practices: spacing, rotation and timing. Thin plants to the recommended spacing as soon as they are large enough to handle; crowded plants run warm and airless, which favours both aphids and mildew. Rotate beds so no Cichorium crop occupies the same ground more than once every two or three years, cutting off the life cycles of soil-dwelling pests and reducing accumulated fungal spore loads. Time sowings for cooler weather where possible; autumn crops are usually healthier than summer ones in a typical UK season.
Inspect plants at least once a week from midsummer, paying particular attention to the growing point where aphid colonies establish earliest. Catching an infestation at five or ten insects is far easier than dealing with thousands. Grow endive in part shade if your site runs warm, particularly in the south, and consider mulching around the base of plants to keep root temperatures stable and reduce moisture stress that makes plants more susceptible to all of the problems above.
Frequently asked questions
Why are my radicchio leaves curling inward?
Inward curling on radicchio is most often caused by lettuce aphid colonies clustered in the heart of the plant. Check the youngest leaves and the growing tip for dense clusters of small pale green or yellow-green insects. Sticky honeydew on surrounding leaves is a strong indicator. Remove heavily infested growth, blast remaining aphids off with water, and apply an insecticidal soap spray in the evening when beneficial insects are less active.
What are the white patches and curled leaves on my endive?
White powdery patches combined with leaf curl and distortion point to powdery mildew caused by Erysiphe cichoracearum. Unlike many fungal diseases, this one thrives in warm dry spells rather than wet conditions. Improve airflow by thinning plants to at least 30 cm apart, remove affected leaves promptly, and apply a potassium bicarbonate or sulphur-based fungicide. Avoid overhead watering in the evening as this raises humidity around the foliage.
My chicory looks wilted and the lower leaves are curling even though the soil is moist. What is wrong?
Wilting and curl at the base of the plant despite adequate moisture strongly suggests lettuce root aphid (Pemphigus bursarius). These woolly white insects feed on the roots and are invisible without lifting the plant. Check for a white waxy powder at or just below soil level around the taproot. Remove and destroy badly affected plants, rotate the bed away from Cichorium crops for at least two years, and consider yellow sticky traps to catch the flying adults that colonise new sites in summer.
Can hot weather cause chicory or endive leaves to curl?
Yes. Both chicory (Cichorium intybus) and endive (Cichorium endivia) are cool-season crops that bolt readily when temperatures climb above about 25 C for extended periods. As a plant begins to bolt, it sends up a flowering stem and the remaining rosette leaves often curl, pucker and become bitter. Choosing bolt-resistant varieties, sowing in late summer for an autumn harvest, and giving plants some afternoon shade in warm spells all reduce this problem. Belgian endive forced in darkness is immune to bolting stress during the forcing stage.
How do I tell powdery mildew apart from downy mildew on my endive?
Powdery mildew (Erysiphe cichoracearum) produces a dry white or grey powdery coating on the upper surface of leaves and is worst in warm dry weather. Downy mildew (Bremia lactucae) causes pale yellow patches on the upper leaf surface with a greyish-white fluffy growth on the underside, and it thrives in cool humid conditions. Both can cause leaf distortion and curl, but the surface where the growth appears and the weather conditions at the time of outbreak are the key distinguishing features.