Why Are My Pea Leaves Curling?

Pea leaf weevil

Pea leaf weevil (Sitona lineatus) is one of the most easily recognised pea pests in UK gardens because of the distinctive scalloped notches the adult beetles eat from the margins of pea and broad bean leaves. The damage looks as though a small hole punch has been applied to the leaf edges, creating regular, rounded notches. Although unsightly, this leaf damage rarely kills the plant or significantly reduces the crop in most years. The more damaging phase is the larval stage underground, where the larvae feed on the nitrogen-fixing root nodules of the pea plant.

What to do

• There are no registered pesticides available to home gardeners for pea leaf weevil control. The damage is generally tolerable and most plants grow through it without significant crop loss.
• Cover young pea plants with fine insect mesh immediately after germination to exclude adult weevils from feeding on the plants when they are most vulnerable. Remove the cover once the plants are well established and growing vigorously.
• Encourage natural predators by maintaining areas of long grass and wildflowers near the vegetable garden. Ground beetles, which overwinter in leaf litter and long grass, are significant predators of pea leaf weevil larvae in the soil.

Pea aphid

Pea aphid (Acyrthosiphon pisum) is a large, pale green aphid that colonises the growing tips, leaf undersides, and flower buds of pea plants from May onward in the UK. Dense colonies cause the young leaflets and tendrils to curl and distort around the aphid clusters, and heavy infestations cause general yellowing of the plant and reduced pod set. Pea aphid also transmits several viruses, including pea enation mosaic virus, which causes mosaic patterning and leaf distortion that persists even after the aphid is controlled.

What to do

• Inspect growing tips weekly from May for pea aphid colonies. Early intervention when colonies are small is much more effective than attempting to control a large, established infestation.
• Remove small colonies by hand or with a strong jet of water. For larger infestations, spray with insecticidal soap solution, covering the growing tips and leaf undersides thoroughly. Repeat every 4 to 5 days for 2 to 3 weeks.
• Avoid growing peas near broad beans, which share many of the same aphid species. Companion planting with summer savory (Satureja hortensis) around peas has a traditional reputation for deterring pea aphid.

Drought and heat

Peas are cool-season vegetables that struggle when UK temperatures exceed 20 degrees Celsius consistently. Drought causes wilting and leaflet curl during the hottest part of the day, and the entire plant may turn yellow and die back prematurely in hot, dry summers. Heat also reduces flower and pod set: flowers drop without setting pods when temperatures are consistently high, leading to reduced yields even from healthy-looking plants.

What to do

• Time pea sowings to avoid peak summer heat: sow from March to late May for crops that mature before midsummer, and again in late July for an autumn crop. This matches the cool-season preference of the crop to the cooler parts of the UK growing season.
• Water consistently during dry spells, particularly when the plants are flowering and setting pods. Irregular watering causes flowers to drop and pods to form incompletely.
• Apply a mulch around the plants to conserve soil moisture and keep the root zone cooler. In exposed, sunny beds, some shading from a neighbouring taller crop can extend the productive season by reducing heat stress.

Powdery mildew

Powdery mildew (Erysiphe pisi) causes white, powdery fungal growth on the upper surface of pea leaves and stems, and affected leaves may curl slightly and take on a pale, dusty appearance. It is most common in late summer when conditions are warm and dry with cool nights, and in the UK it typically appears in August and September on plants that have been in the ground since spring. It rarely kills the plant outright but reduces photosynthesis and can cause premature leaf death.

What to do

• Remove severely affected leaves and stems to reduce the spread of fungal spores. Do not compost powdery mildew-affected material as the spores can survive in the compost heap.
• Improve airflow around plants by thinning overcrowded stems and ensuring adequate spacing between plants at sowing. Powdery mildew thrives in still, humid air around dense plantings.
• Water at the base of the plant rather than overhead to avoid wetting the foliage, which can encourage fungal development. Drip irrigation or careful hand watering at root level is preferable to overhead sprinklers for peas.

Root problems

Root rot caused by Aphanomyces euteiches, Fusarium species, and Pythium species causes pea plants to wilt, yellow, and die despite adequate watering. The roots of affected plants are brown, soft, and rotted rather than white and firm. Root rot is most common in waterlogged or compacted soils, in cold wet springs, and in soils with a long history of pea growing without crop rotation.

What to do

• Rotate peas (and broad beans) to a different bed every year, aiming for a minimum 3-year gap before growing peas in the same position again. The soil pathogens responsible for root rot persist in the soil and build up when peas are grown repeatedly in the same location.
• Improve drainage in waterlogged beds by raising the growing surface into beds above the surrounding level, or by incorporating grit and compost to break up compacted soil. Peas absolutely require well-drained soil to avoid root rot in wet UK springs.
• Remove and destroy affected plants and do not compost them. Avoid watering the bed excessively during cool, wet spring conditions.

Frequently asked questions

Why are my pea leaves curling?

Pea leaves curl most often from pea leaf weevil damage, aphid infestation, or drought. Pea leaf weevil (Sitona lineatus) adults eat distinctive scalloped notches from the edges of pea leaves, and heavy feeding causes the leaflets to curl and appear tattered. Pea aphid (Acyrthosiphon pisum) colonises growing tips and leaf undersides, causing the young leaves and tendrils to distort and curl around the feeding colonies. Drought causes the entire plant to wilt and the leaflets to curl inward along their length. All three causes are common in UK vegetable gardens from April onward.

What are the scalloped notches on my pea leaves?

Scalloped notches eaten from the edges of pea and broad bean leaves are the characteristic damage signature of pea leaf weevil (Sitona lineatus). The adult weevils are small, grey-brown beetles about 5mm long that feed on leaf margins from late winter through spring and into summer. The notching is rarely severe enough to kill the plant and is more cosmetic than harmful in most years. However, the larvae of pea leaf weevil feed on the nitrogen-fixing root nodules of peas and beans, reducing the plant's ability to fix atmospheric nitrogen. In a heavy infestation year, larvae can cause significant yield reduction even when leaf damage appears modest.

Why are my pea plants wilting despite regular watering?

Pea plants wilt despite regular watering most often from root rot (caused by Aphanomyces or Pythium species in wet, cold soils), pea root rot fungal infection, or crown rot. Unlike drought wilt, which recovers overnight, root rot wilt is permanent: the plant may appear to recover slightly in cool conditions but progressively deteriorates. Pulling up an affected plant reveals brown, rotted roots rather than the white, healthy roots of a well-grown plant. Root and crown rot is most common in cold, waterlogged conditions in early spring and in soils where peas have been grown repeatedly in the same position without rotation.

How should peas be grown in the UK?

Garden peas (Pisum sativum) grow best in the UK when sown from March to June in a sunny, sheltered position in fertile, well-drained soil. They are cool-season vegetables that prefer temperatures between 10 and 20 degrees Celsius and perform poorly in hot summers. Taller varieties need support from netting, canes, or pea sticks. Peas fix their own nitrogen from the atmosphere through root nodules and do not need nitrogen fertiliser; in fact, nitrogen-rich soil encourages lush leaf growth at the expense of pod production. A rotation of at least 3 years is recommended to avoid the build-up of pea-specific soil pathogens such as Aphanomyces euteiches, which causes root rot.