Parsnips are prone to canker, a spore driven fungal disease that causes the roots to rot. This starts to happen as cooler, damper and windier weather comes in over the autumn. Canker is normally seen in the crown/shoulder of the parsnip, although you may see signs of it on foliage too (it’ll look a lot like leaf spot). The root will develop orange/brown coloured patches where it will start to rot.
If you have heavy soil, your crops will be more at risk of developing canker, particularly if drainage is poor. You’ll also find that damaged roots will be more affected, so if you’ve accidentally forked a parsnip, or if carrot root fly/slugs have damaged the roots at all, they are more susceptible.
At this time of year, it is a good idea to earth up your parsnips to ensure that the crowns are not exposed, this will help to protect them from spores over the coming weeks. It won’t guarantee that your plants will be unaffected, but it’ll certainly help. Simply bury any exposed crowns with some good quality compost.
If your parsnips do get affected, you can simply pull them up, cut off the affected parts and use them as normal.