Why Are My Beetroot Leaves Curling?

Beet leaf miner

Beet leaf miner (Pegomya hyoscyami), also called mangold fly, is the most common pest of beetroot leaves in UK gardens. The adult fly lays eggs on the underside of leaves in spring and early summer; the larvae hatch and mine into the leaf tissue, feeding between the upper and lower leaf surfaces and creating characteristic pale, blistered, transparent patches where the internal tissue has been consumed. The affected areas turn brown and papery as the mined tissue dies, and the surrounding leaf may curl around the damage. There are two to three generations per year, with damage most visible from May through to September.

What to do

• Remove and destroy badly affected leaves promptly to kill the larvae inside them and reduce the population available for subsequent generations. The larvae are visible as small, pale maggots when mined leaves are torn open.
• Crush visible larvae in the leaf by pressing the blistered area between thumb and forefinger, killing them without removing the leaf.
• Cover beetroot sowings with fine insect mesh from sowing through the main fly activity period to prevent egg-laying on the leaves. This is most worthwhile for early sowings in April and May when the first-generation attack is most damaging.
• Leaf miner rarely causes serious harm to established beetroot plants with well-developed root systems: even substantially mined foliage continues to support root development, so minor attacks do not require urgent action.

Drought

Beetroot is relatively drought-tolerant compared with some other vegetables, but drought during the growing season produces woody, pithy roots with a stronger, less sweet flavour than well-watered beetroot. The leaves of drought-stressed plants wilt and curl inward during hot periods. Irregular watering that alternates between drought and flood causes roots to crack or develop uneven growth rings.

What to do

• Water beetroot during dry spells to maintain consistent soil moisture, particularly during the period of rapid root swelling from June onward. A deep watering every 10 to 14 days in dry conditions is more effective than frequent shallow watering.
• Apply a mulch of compost between the rows to conserve soil moisture and suppress competing weeds.
• Harvest beetroot promptly when the roots reach a useful size: roots left too long in the soil during hot, dry weather become woody and tough regardless of watering.

Aphids

Black bean aphid (Aphis fabae) and peach-potato aphid (Myzus persicae) both colonise beetroot, typically on the underside of leaves and at the growing tips. Aphid feeding causes the leaves to curl and pucker around the feeding sites. Heavy infestations stunt growth and may distort the developing roots. Aphid honeydew promotes sooty mould growth on the affected leaves.

What to do

• Inspect the underside of beetroot leaves from May for aphid colonies. Small colonies can be squashed by hand or removed with a strong jet of water.
• Apply insecticidal soap spray to larger colonies, covering the underside of affected leaves. Repeat every 5 to 7 days. Natural predators including ladybirds and hoverfly larvae typically provide good aphid control on beetroot by mid-summer.

Downy mildew

Downy mildew on beetroot (caused by Peronospora farinosa f. sp. betae) produces pale, angular patches on the upper surface of the leaves with a grey-purple downy growth below. Affected leaves curl and yellow. The disease is most common on crowded, poorly ventilated plants in cool, humid conditions, and is more severe on overwintered or densely sown crops.

What to do

• Thin beetroot to the correct spacing as early as possible: 10 centimetres for small roots or 15 to 20 centimetres for larger ones. Dense sowing is a common cause of downy mildew on beetroot.
• Remove and destroy affected leaves promptly. Rotate beet family crops (beetroot, chard, spinach) each year to different beds.

Bolting

Bolting (running to seed prematurely) on beetroot causes the plant to produce a tall flower stem rather than continuing to swell the root. Once a plant bolts, the root becomes woody and unpalatable. Beetroot is triggered to bolt by exposure to cold temperatures followed by warming, which mimics the conditions of winter followed by spring that signal to the plant that it is time to flower and set seed. This is most common with very early sowings (before late March) or in cold, fluctuating springs.

What to do

• Avoid sowing beetroot outdoors before late March to mid-April: early sowings in cold soil are more likely to experience the temperature fluctuations that trigger bolting.
• Choose bolt-resistant varieties for early sowings: 'Boltardy' is the most widely available bolt-resistant UK variety and is specifically bred for early sowing.
• Remove any bolted plants promptly and use any usable root immediately, as the root quality deteriorates rapidly once the plant has bolted.

Frequently asked questions

Why are my beetroot leaves curling?

Beetroot leaves curl most often from beet leaf miner damage, drought, or mangold fly. Beet leaf miner (Pegomya hyoscyami) larvae tunnel between the layers of beetroot leaves, causing pale, blistered patches that cause the leaf to curl around the mining damage. Drought causes the leaves to wilt and curl inward during hot, dry periods, recovering when the soil is watered. The leaf edges may also curl if the soil pH is very low or if there is a boron deficiency, both of which are addressed by liming and balanced feeding.

What are the blistered patches on my beetroot leaves?

Blistered, pale, papery patches on beetroot leaves are most likely caused by beet leaf miner (Pegomya hyoscyami), the larva of a small fly that mines between the upper and lower leaf surfaces. The larvae consume the tissue between the leaf layers, leaving transparent, blister-like patches that turn brown and papery as the mined tissue dies. The surrounding leaf often curls around the damaged area. Leaf miner on beetroot is common in UK gardens and rarely causes serious harm to established plants; the roots continue to develop normally even when the foliage is substantially mined. Remove and destroy badly affected leaves to reduce larval populations.

Can you eat beetroot leaves?

Beetroot leaves are completely edible and nutritious. Young, tender leaves can be eaten raw in salads, where their mild, earthy flavour is similar to spinach. Older leaves are best cooked: steam them, wilt them in a pan with olive oil, or add them to soups and stews. The red-veined younger leaves of red beetroot varieties are particularly attractive as salad leaves. Harvesting the outer leaves as the plant grows does not significantly harm the developing root, provided the growing tip and sufficient inner leaves are left intact to continue photosynthesising.

When should I sow beetroot in the UK?

Beetroot is sown in the UK from late March (under cover or with cloche protection) through to mid-July for successional harvests. The main outdoor sowing season is April to late June. Beetroot germinates best in soil temperatures of 10 to 25 degrees Celsius and may be slow to germinate in cold spring soils; sowing under a cloche or on a warm windowsill for the earliest crops helps. Soak the corky seed clusters in water for a couple of hours before sowing to speed up germination. Each cluster typically produces 2 to 3 seedlings and should be thinned to the strongest one, with final spacings of 10 centimetres for golf-ball sized roots or 15 to 20 centimetres for full-sized roots.