Parsnip canker

Parsnip canker is a disease which causes parsnip roots to blacken, crack and eventually rot.

Symptoms
Symptoms include; black or orange patches on the roots. The patches usually occur near the shoulder of the roots and the crown of the plants. In severe cases, the roots crack and rot. There are two kinds.

Black canker
Black canker is actually tinged purple. It is considered to be mainly caused by the fungus Itersonilia pastinacae. Other fungi thought to be involved are Phoma and Mycocentrospora acerina.

Brown or orange canker
This is thought to be caused by an invasion of the same fungus (I. pastinacae). It is not usually damaging, but it gets into damaged roots. It is also responsible for leaf-spot disease.

Treatment
No chemicals have been found that prevent or cure the disease.

Prevention
Improving drainage, by putting in drains, double-digging to destroy compacted soil and making raised beds, will reduce the severity. Improving drainage can be difficult on clay soils however. Adding organic matter, such as mushroom compost, wellrotted manure and garden compost, will improve the soil structure, which in turn enhances drainage. Although it is often said that manuring causes fanged or forked roots, there is no evidence that this is the case. If your soil is acid, add lime to raise the pH to 6.5. If you don’t know the pH use a cheap kit for a rough-and-ready pH determination.

Resistance varieties
Resistant varieties should always be used where canker is a problem. They are the most cost-effective control measure although cannot be guaranteed.

Resistant varieties include:
 * ‘Alba’
 * ‘Arrow’
 * ‘Avonresistor’
 * ‘Bayonetta’
 * ‘Cobham Improved’
 * ‘Gladiator’,
 * ‘Imperial Crown’
 * ‘Javelin’
 * ‘Marrow Improved’
 * ‘White Gem’
 * ‘White Spear’