Garden peas (Pisum sativum), mange tout, and sugar snap peas are among the most satisfying crops to grow in a UK allotment or veg patch. When the leaves start to curl, pucker, or distort, it is almost always a sign that one of two problems has taken hold. Identifying the culprit early means you can act before yields suffer.
What causes pea leaves to curl?
The vast majority of curling and distortion on pea plants comes down to pea aphids or powdery mildew. Both are extremely common in the UK, and both are manageable once you know what you are dealing with. In some cases a combination of the two is present at the same time, especially later in the season when plants are under stress. A handful of other causes are worth ruling out if the two main suspects do not match your symptoms.
1. Pea aphids (Acyrthosiphon pisum)
Pea aphids are large, pale green insects, noticeably bigger than the blackfly you see on broad beans. They colonise the soft growing tips, stems, and undersides of leaves from late spring onwards, forming dense clusters that can number in the hundreds within days. As they feed, they pierce the plant tissue and extract sap, which causes leaves to curl downwards and inwards, sometimes quite dramatically. You may also notice a sticky, shiny residue on the leaves (honeydew), which can in turn encourage a sooty black mould to develop. Yellowing of leaves near heavily infested areas is common. Ants running up and down the stems are a reliable indicator as well; they farm aphids for the honeydew and will actively protect colonies from predators.
How to fix it
For small infestations, simply squash the colonies between your fingers or knock them off with a firm jet of water. Repeat every two or three days until numbers drop. For more persistent problems, spray with an insecticidal soap solution (available from any garden centre), making sure to coat the undersides of leaves where the aphids shelter. Neem oil works on the same principle and can be used as an alternative. Avoid high-nitrogen feeds on peas at all costs; lush, soft growth is exactly what aphids are attracted to, and peas fix their own nitrogen anyway. The most effective long-term control is encouraging natural predators. Ladybirds and their larvae eat enormous numbers of aphids, as do hoverfly larvae. Planting flowers such as phacelia, pot marigold, or sweet alyssum near your peas will draw in hoverflies throughout the season.
2. Powdery mildew (Erysiphe pisi)
Powdery mildew is a fungal disease specific to the legume family. It is particularly common on peas in the UK from mid-summer onwards, when days are warm and dry but nights are cool and humid. The first sign is usually a pale grey-white powdery coating on the upper surface of the leaves. As the infection spreads, leaves curl, pucker, and become distorted; in severe cases the whole plant looks bleached and stunted. Mange tout and sugar snap varieties can be affected just as badly as shelling peas. The spores travel easily on the wind, so an infection can spread across an entire row within a week or two if conditions are right. Plants under any form of stress, including drought or crowding, are significantly more vulnerable.
How to fix it
There is no spray that will remove powdery mildew once it has taken hold, but you can slow its progress. Start by removing the worst-affected leaves and stems and disposing of them in the bin rather than the compost. Improve airflow around the plants by thinning them out if they are crowded, and make sure you are watering at soil level rather than overhead; wet foliage encourages the fungus. A fortnightly spray of diluted bicarbonate of soda (one teaspoon per litre of water with a few drops of washing-up liquid) can help suppress the disease, though results are variable. The most reliable approach for future seasons is to grow resistant varieties. Sugar Ann is widely recommended and widely available from UK seed suppliers. Sowing earlier in the season so that pods are harvested before the hot, dry conditions of late July and August also makes a significant difference.
Other causes to consider
If neither aphids nor powdery mildew match your symptoms, consider the following. Pea and bean weevil (Sitona lineatus) causes characteristic scalloped notching around the edges of leaves rather than curling, but a heavy infestation can cause the leaves to look distorted. The adult weevils feed at night and are rarely seen. Pea moth (Cydia nigricana) targets pods rather than leaves, but larvae tunnelling inside the pods can cause plants to look stressed and the foliage to flag. Drought stress causes the tendrils and leaf tips to curl inward; check the soil a few centimetres down and water thoroughly if it is dry. Finally, pea leaf roll virus causes yellowing, downward rolling, and stunting that can look similar to aphid damage. It is spread by aphids, so controlling aphid populations is the best way to prevent it. There is no treatment for the virus itself; affected plants should be removed and binned.
How to keep peas healthy
- Sow at the right time. Aim for March to May in most parts of the UK, or use an autumn-sowing variety for an early June crop. Late sowings that mature in August are the most mildew-prone.
- Support plants properly with sticks, pea netting, or twiggy branches. Good support improves airflow and keeps foliage off the ground, reducing the risk of fungal disease.
- Water at root level, not overhead. A soaker hose or careful watering with a can placed at the base of the plant keeps foliage dry and significantly reduces powdery mildew pressure.
- Space plants generously. Crowded rows trap humidity and make it easier for both aphids and fungal spores to spread. Follow the spacing on the seed packet.
- Rotate your crops. Do not grow peas (or other legumes such as broad beans or French beans) in the same bed more than once every three years. Rotation helps break pest and disease cycles in the soil.
Frequently asked questions
Why are the tips of my pea plants curling?
Curling at the tips is most often caused by pea aphids feeding on the soft growing points. Check the undersides of leaves and the tender stem tips for clusters of pale green insects. Drought stress can also cause the tendrils and leaf tips to curl inward as the plant conserves moisture; push a finger a few centimetres into the soil to check whether it needs water.
Can I eat peas from plants that have had aphids?
Yes. Once you have dealt with the aphids and the plant is growing strongly again, any pods that develop are perfectly safe to eat. Rinse pods under cold water before podding or eating them. Mange tout and sugar snap varieties are fine to eat whole after a thorough wash. There is no need to discard a harvest just because aphids were present earlier in the season.
How do I tell powdery mildew from other pea problems?
Powdery mildew produces a distinctive white or pale grey powdery coating on the upper surface of leaves. It does not wash off with rain and spreads rapidly in warm, dry weather with cool nights. Downy mildew, by contrast, shows as yellowing on the top of leaves with a grey-purple fuzz on the underside. Aphid damage causes curling and a sticky residue but produces no white coating. If you see the white powder, powdery mildew is almost certainly the cause.
Should I remove pea plants with powdery mildew?
Not necessarily. If the infection is light and there are still pods forming, improving airflow and removing the worst-affected leaves is usually enough to keep the plant cropping until the end of the season. If the plant is heavily affected and has stopped producing well, pull it up and dispose of it in the bin rather than the compost heap, to avoid spreading spores. Do not leave affected debris on the soil over winter.