Allotments 4 All

In the last 4 days the leaves of my parsnips have been eaten by hordes of small maggots about 4mm long and have gone from green to black dust. Can anyone help? A neighbour says carrot fly but I thought they attacked the carrot or parsnip, not the leaves. ???

Think it may be the larvae of a pest called celery fly. You can squash the maggots off by hand, or spray with an insecticide.
If celery, carrots etc are nearby, this may encourage the pest.