Canker

DESCRIPTION
This is the most serious problem with parsnips.  It appears as firm brown or black patches on the shoulder of the root which then becomes soft and rotten. The secondary rotting which follows the initial discolouration is caused by fungi or bacteria.  It is more likely though that the infected roots have been damaged in some way, perhaps by carrot fly, by cracking caused by heavy rain after drought or by careless hoeing.  Because parsnips are not self healing, soil borne fungi and bacteria can enter and rot the roots.

TREATMENT
The only remedy is better cultivation.  Acid soil and over manuring with unrotted manure are said to encourage canker and these should be avoided.  Try also later sown crops, as these are more resistant.