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Carrot Fly
The greenish-black carrot fly
lays its eggs in the soil near carrots, parsnips or celery to which it is
attracted by the smell of the foliage. The eggs hatch to produce
small, pale yellow maggots which invade the roots.
These pests are
also a problem because the wounds they cause provide a starting point for
canker. Carrot fly is most likely just after thinning because the smell of
the damaged foliage attracts them. Thin seedlings in the evening when the
flies are less likely to be active, and burn all the thinned plants.
Firm the soil around the base of the plants after thinning as this fills in the cracks
in the soil and deters the flies from laying eggs.