Why Are My Parsnip Leaves Curling?

Carrot-willow aphid

Carrot-willow aphid (Cavariella aegopodii) is the most common aphid pest of parsnips and carrots in the UK. It alternates between willows (its winter host) and umbellifers (carrot family plants including parsnip, carrot, parsley, and celery) in summer. On parsnips, it feeds at the growing tip and on the underside of the youngest leaves, causing the young leaves to curl, crinkle, and distort as they develop. Colonies are often green to yellowish and can be difficult to spot among the ferny foliage.

What to do

• Inspect the growing tips of parsnip plants regularly from late spring. The aphids congregate at the youngest growth, so focus inspections there rather than on the mature leaves.
• Apply insecticidal soap spray to affected growing tips, covering the underside of curled leaves as thoroughly as possible. Repeat every 5 to 7 days.
• Fine insect mesh over the crop from sowing through the main aphid flight season (April to June) prevents most aphid infestations. Carrot-willow aphid can also transmit carrot viruses, so mesh protection benefits the crop in more than one way.

Parsnip canker

Parsnip canker is the most destructive disease of parsnips in the UK, causing orange-brown, sunken, rotten areas at the crown and shoulder of the root. In severe cases, the infection progresses up into the foliage, causing the lower leaves to yellow and collapse. It is caused by a complex of fungal pathogens that enter primarily through wounds or natural openings at the root shoulder. Roots that have been damaged by carrot fly larvae, hoeing, or soil disturbance are especially vulnerable.

What to do

• Rotate parsnips to a new bed each year: the canker-causing pathogens persist in the soil and crop debris, and returning parsnips to the same ground in successive years increases disease pressure.
• Hoe carefully to avoid nicking parsnip roots with the hoe blade; hand-weed close to the plants once the roots are developing.
• Grow canker-resistant varieties: 'Javelin', 'Gladiator', 'Albion', and 'Tender and True' all have reasonable canker resistance and are widely available in UK seed catalogues.
• Avoid adding fresh manure or high-nitrogen fertilisers to parsnip beds, which create soft, fast-growing tissue that is more susceptible to canker entry.

Drought

Drought causes parsnip leaves to wilt, droop, and curl inward. More importantly for the harvest, drought during the growing season produces woody, pithy, or split roots rather than the smooth, sweet roots expected from a well-grown crop. Irregular watering that alternates between drought and flood is particularly damaging, causing roots to crack as they take up water rapidly after a dry period. Parsnips have deep taproots and are more drought-tolerant than some vegetables, but consistent moisture through the growing season significantly improves root quality.

What to do

• Water parsnips during prolonged dry spells in summer to prevent drought stress. Deep watering every 10 to 14 days is better than frequent shallow watering, as it encourages the roots to extend downward into the moister subsoil.
• Apply a mulch of compost between the rows to conserve soil moisture and suppress weeds. Weeds compete strongly with parsnips for water during the long growing season.

Carrot fly

Carrot fly (Psila rosae) attacks parsnips as well as carrots, and the symptoms are very similar on both crops. The larvae of carrot fly tunnel into the roots, creating rust-coloured channels just below the skin. Heavily attacked roots turn rusty-brown under the skin, and the foliage of severely infested plants may yellow and wilt as root function is compromised. Carrot fly attacks parsnips less severely than carrots, but the crop is still susceptible and should be protected in areas where carrot fly is established.

What to do

• Cover parsnip sowings with fine insect mesh from sowing to harvest. Carrot fly is a low-flying pest that navigates by smell; mesh prevents the female fly from reaching the crop to lay eggs.
• Avoid thinning or weeding parsnips during the main carrot fly flight periods (May to June and August to September): the crushed foliage releases carrot-family scent that attracts egg-laying females from a distance.

Leaf miners

Parsnip leaf miner (Euleia heraclei) is a fly whose larvae mine between the layers of parsnip leaves, creating pale, winding tunnels visible against the surface of the leaf. Affected leaves may curl around the mining damage. Leaf mining rarely causes serious damage to healthy, established parsnip plants but can disfigure the foliage and weaken seedlings if attacks are severe early in the season.

What to do

• Remove and destroy individual mined leaves to kill the larvae inside them. The larvae are very small and difficult to target with sprays; removing the mined tissue is more effective than spraying.
• Fine insect mesh over the crop from sowing prevents the adult fly from laying eggs on the leaves.

Frequently asked questions

Why are my parsnip leaves curling and yellowing?

Parsnip leaves curl and yellow most often from parsnip canker, drought, or aphid infestation. Parsnip canker (a complex of fungal pathogens) primarily attacks the crown and roots of the parsnip, but severe infection causes the foliage to yellow and collapse. Drought causes the ferny, divided leaves to wilt, droop, and curl inward. Carrot-willow aphid (Cavariella aegopodii) colonises parsnip leaves, particularly in spring, causing the young leaves at the growing tip to curl and distort around the aphid colonies.

What is parsnip canker and how do I prevent it?

Parsnip canker is the most common disease of parsnips in UK gardens. It causes orange-brown, sunken, rotten patches on the top of the root (the crown and shoulder), which can spread into the root flesh. Canker is caused by a complex of fungal pathogens that enter through damaged tissue or through natural openings. Prevention focuses on: sowing in a different bed each year (crop rotation); avoiding root damage during weeding (hoeing close to parsnips cuts into roots and creates entry points for canker); growing canker-resistant varieties such as 'Javelin', 'Gladiator', or 'Albion'; and avoiding overfertilising with nitrogen, which creates soft, fast-growing tissue more susceptible to infection.

When can I harvest parsnips in the UK?

Parsnips are ready to harvest in the UK from October onward, but they are at their best after the first hard frosts of winter. Cold temperatures convert the starches in the root to sugars, giving properly frosted parsnips their characteristic sweet, nutty flavour. Parsnips can be left in the ground throughout winter and harvested as needed: they are completely frost-hardy and actually improve in flavour after each frost. The foliage will die back naturally in autumn; the roots remain in excellent condition in the ground until spring, when they will begin to regrow and the roots will deteriorate. In practice, parsnips are best harvested by March before new growth begins in earnest.

Is parsnip sap dangerous?

Parsnip sap (and the sap of related plants in the carrot family including giant hogweed) can cause phototoxic burns on skin in bright sunlight. The sap contains furanocoumarins, compounds that react with ultraviolet light to cause burns, blisters, and long-lasting skin discolouration. This reaction (phytophotodermatitis) can occur from contact with bruised or damaged parsnip leaves and stems. When harvesting, thinning, or weeding around parsnips in bright sunshine, wear long sleeves and gloves or wash any skin that comes into contact with the sap before going into direct sunlight. The risk is highest in warm, sunny conditions when the plants are actively growing and the sap is most concentrated.