structural:reformatting, stylistic:tone, quality:corruption, stylistic:style_transfer
Problems

Parsnip leaves are sometimes tunnelled by the larvae of the celery fly (Euleia heraclei). Irregular, pale brown passages can be seen between the upper and lower surfaces of the leaves. The effects are most serious on young plants, as whole leaves may shrivel and die. Treatment is by removing affected leaflets, whole leaves, or by chemical means.

The crop can be attacked by larvae of the carrot fly (Chamaepsila rosae). This pest feeds on the outer layers of the root, burrowing its way inside later in the season. Seedlings may be killed while larger roots are spoiled. The damage done provides a point of entry for fungal rots and canker. The smell of bruised tissue attracts the fly.

Parsnip is used as a food plant by the larvae of some lepidopteran species, including the parsnip swallowtail (Papilio polyxenes), the common swift moth (Korscheltellus lupulina), the garden dart moth (Euxoa nigricans), and the ghost moth (Hepialus humuli). The larvae of the parsnip moth (Depressaria radiella), native to Europe and accidentally introduced to North America in the mid-1800s, construct their webs on the umbels, feeding on flowers and partially developed seeds.

Parsnip canker is a serious disease of this crop. Black or orange-brown patches occur around the root's crown and shoulders, accompanied by cracking and hardening of the flesh. It is more likely to occur when the seed is sown into cold, wet soil, the pH of the soil is too low, or the roots have already been damaged by carrot fly larvae. Several fungi are associated with canker, including Phoma complanata, Ilyonectria radicicola, Itersonilia pastinaceae, and I. perplexans. In Europe, Mycocentrospora acerina has been found to cause a black rot that kills the plant early. Watery soft rot, caused by Sclerotinia minor and S. sclerotiorum, causes the taproot to become soft and watery. A white or buff -coloured mould grows on the surface. The pathogen is most common in temperate and subtropical regions with a cool, wet season.

Violet root rot caused by the fungus Helicobasidium purpureum sometimes affects the roots, covering them with a purplish mat to which soil particles adhere. The leaves become distorted and discoloured, and the mycelium can spread through the soil between plants. Some weeds can harbour this fungus, and it is more prevalent in wet, acid conditions. Erysiphe heraclei causes a powdery mildew that can cause significant crop loss. Infestation by this causes results in the yellowing of the leaf and loss of foliage. Moderate temperatures and high humidity favor the development of the disease.

Several viruses are known to infect the plant, including seed-borne strawberry latent ringspot virus, parsnip yellow fleck virus, parsnip leaf curl virus, parsnip mosaic potyvirus, and potyvirus celery mosaic virus. The latter causes clearing or yellowing of the areas of the leaf immediately beside the veins, the appearance of ochre mosaic spots, and the crinkling of the leaves in infected plants.