Carrot root fly is probably the most serious pest of carrot crops. Although affected roots can still be eaten, it does reduce the amount of usable root and it can take ages in the kitchen cutting out the affected parts.
Carrot root fly adults are small and you'd be hard pressed to recognise them or see them flying around. They lay their eggs at the base of the developing carrot plant.
The larvae bury into the roots of carrots, parsnips, celery and celeriac causing disfiguring black 'mines'. This then leads to the roots rotting.
The foliage usually turns yellow, orange or red in colour and may wilt. The roots are tunnelled by maggots.
No chemical treatment is available, but the following cultural advice is helpful.