Why Are My Beetroot Leaves Curling?

Black bean aphid

Aphis fabae is an extremely common UK garden pest of beetroot and chard from May to August. The very dense, shiny-black, sometimes waxy-powdery aphid colonies develop on leaf undersides and in a mass around the growing points; heavy feeding at the growing tips causes the developing young leaves to curl tightly inward, enclosing the aphid colony within rolled leaf tissue. Colonies arrive from spindle tree (Euonymus europaeus) in late May to early July.

What to do

• Check plants from May onward; squash or rub off small colonies with fingers or a damp cloth; knock larger colonies off with a forceful jet of water from a hosepipe; pinch out and discard the growing tip with its enclosed aphid colony (particularly effective on chard where the outer leaves are unaffected); encourage natural predators (ladybirds, lacewing larvae, hoverfly larvae); apply insecticidal soap spray directly to the colonies if needed; check the edible crop withholding period on the product label.

Beet leaf miner (mangold fly)

Pegomya hyoscyami lays eggs on beetroot and chard leaf undersides; the hatching maggots create pale, papery, blister-like leaf mines between the upper and lower leaf surfaces. Multiple maggots may share a single blister. Two to three generations per year in UK conditions: first generation mines in May and June, second in July and August. Very visible and alarming, but overall impact on beetroot root harvest is often less severe than it initially appears.

What to do

• Squeeze each mine firmly between thumb and forefinger to kill the maggot inside; check plants every three to four days during peak mining periods (May to June and July to August); remove and dispose of very extensively mined leaves in general waste (not compost); cover beetroot and chard plants with fine insect-proof mesh (approximately 1 to 1.5 mm mesh) immediately after sowing, securing and weighting the edges; the mesh must remain in place until harvesting to prevent the adult fly from accessing the leaves to lay eggs.

Cercospora leaf spot

Cercospora beticola is the most widespread and most economically important fungal disease of beetroot and chard worldwide. Causes circular or irregular pale brown or tan-centred spots with a characteristic reddish-purple or dark red border; in severe infections the spots coalesce, the leaves yellow, curl, and die from the centre outward. Most common in warm, wet, humid UK summer conditions from July to September.

What to do

• Ensure adequate spacing between plants for good air circulation; avoid overhead irrigation and aim to water at the base of the plants in the morning; remove and dispose of the most severely spotted leaves in general waste (not compost); rotate beetroot and chard to a different bed each year and do not grow on the same ground more often than once every three to four years to break the disease cycle; choose leaf-spot-resistant varieties where available for new sowings.

Downy mildew

Peronospora schachtii primarily affects young seedlings of beetroot and chard in cool, wet spring conditions. The affected young seedling leaves thicken, curl downward, and develop a pale greyish-purple downy cottony coating on the undersides; the upper surface of the affected young leaf is pale green-yellow. Seedlings can be killed in severe infections.

What to do

• Improve air circulation around the seedlings; avoid overwatering seedlings in cold, wet spring conditions; thin seedlings promptly to the correct spacing to reduce overcrowding; do not transplant seedlings from obviously infected batches; start beetroot and chard seeds in modules under cover in spring for planting out when conditions are warmer and drier, which reduces seedling downy mildew risk compared with direct outdoor sowing in a cold, wet spring.

Frequently asked questions

Why are my beetroot leaves curling?

Beetroot and chard leaves curl most commonly because of black bean aphid (Aphis fabae; very dense shiny-black sometimes waxy-powdery aphid colonies on leaf undersides and around growing points; heavy feeding at growing tips causes developing young leaves to curl tightly inward enclosing the colony in rolled leaf tissue; check plants from May onward; squash or rub off small colonies; knock larger colonies off with forceful jet of water from hosepipe; pinch out growing tip with its enclosed colony; encourage natural predators; insecticidal soap spray directly to colonies if needed), beet leaf miner (Pegomya hyoscyami; pale papery blister-like leaf mines between upper and lower leaf surfaces; squeeze each mine firmly between thumb and forefinger to kill the maggot inside; check plants every 3 to 4 days during peak mining periods May to June and July to August; cover with fine insect-proof mesh approximately 1 to 1.5 mm mesh immediately after sowing), Cercospora leaf spot (Cercospora beticola; circular or irregular pale brown or tan-centred spots with characteristic reddish-purple or dark red border; coalesce in severe infections; leaves yellow curl and die; most common in warm wet humid UK summer conditions July to September; adequate spacing; water at base in morning; rotate beetroot and chard to different bed each year), or downy mildew (Peronospora schachtii; primarily affects young seedlings in cool wet spring conditions; affected young leaves thicken curl downward and develop pale greyish-purple downy coating on undersides; improve air circulation; avoid overwatering seedlings; thin promptly to correct spacing).

How do I control black bean aphid on beetroot?

Life cycle in UK conditions: black bean aphid over-winters as eggs on spindle tree (Euonymus europaeus); eggs hatch in spring; winged aphid forms fly from spindle tree to summer host plants (beetroot chard perpetual spinach broad beans nasturtiums and many others) from approximately late May to early July in UK conditions; timing of migration varies with weather but is often most intense in June. Cultural and physical controls: examine beetroot and chard plants from May onward for first signs of colonies; catching and controlling colonies when small (a few dozen individuals) is much easier than controlling a very large established colony; squash or rub off small colonies directly with fingers or damp cloth; knock larger colonies off with forceful jet of water from hosepipe directed at undersides of leaves; the main colony is often tightly concentrated around the growing tip and this can simply be removed by pinching out the growing tip and its enclosed aphid colony (particularly effective for chard and perpetual spinach where removing the central growing point does not damage the outer leaves). Biological control: encourage natural predators (ladybirds lacewing larvae hoverfly larvae parasitic wasps) in the garden; avoid using broad-spectrum insecticides that kill these beneficial insects. Chemical control: insecticidal soap spray (potassium soap) applied directly to the aphid colonies on the leaf undersides and around the growing points is the most appropriate chemical control for kitchen garden use; always check the edible crop withholding period on the product label before harvesting.

What is beet leaf miner and how do I control it?

Identification: adult mangold fly is a small grey fly approximately 5 to 7 mm long; lays white elongated ribbed eggs (approximately 1 mm long) in small clusters of 2 to 5 on undersides of beetroot and chard leaves; hatching maggots (pale cream to whitish legless approximately 6 to 8 mm when fully grown) burrow between upper and lower leaf surfaces creating characteristic pale papery blister-like leaf mines; multiple maggots may share a single blister; 2 to 3 generations per year in UK conditions: first generation mines in May and June second in July and August sometimes partial third in September. Management: squeeze each mine between thumb and forefinger firmly to kill the maggot inside (you can often feel the maggot as a slight resistance when you squeeze correctly); check plants every 3 to 4 days during peak mining periods; very badly mined leaves can be removed entirely and disposed of in general waste (not compost). Covering with insect-proof mesh: covering beetroot and chard plants with fine insect-proof mesh (approximately 1 to 1.5 mm mesh size) immediately after sowing or planting prevents the adult mangold fly from accessing the leaves to lay eggs; mesh must be laid flat on the ground with edges secured and weighted down; remains in place until harvesting; very effective preventative measure that avoids the need for any other control.

Can you eat beetroot leaves that have been damaged by leaf miner?

Safety: the leaf miner larvae (maggots) themselves are entirely harmless; they have no toxins; there is no food safety concern from consuming leaf-mined beetroot or chard leaves (other than the fact that the maggots are inside the mines which most people prefer to avoid eating). Palatability: the areas of the leaf blade that have been mined (the pale papery blister-like tunnels between the upper and lower leaf surfaces) are unpleasant to eat; the tissue in the mines is dead dry and papery rather than crisp and succulent. Practical advice: cut off and discard the specific mined portions of the leaf blade leaving the healthy green remaining leaf tissue; the remaining leaf tissue between and around the mines is completely normal to eat; only remove and discard entirely those leaves where the mining damage is so extensive (more than approximately half to two-thirds of the leaf blade) that the remaining healthy tissue is negligible; the developing beetroot root below ground is entirely unaffected by leaf miner damage to the leaves above ground (except that very severe extensive leaf damage that defoliates the plant significantly may reduce the size of the developing root below ground).