What is celery leaf mining fly?

Adult celery leaf mining flies are light brown to black flies, with a yellow thorax, they are approximately 5mm long. The larvae are white, legless and headless maggots that feed in groups within the leaves of celery and related plants. The larvae reach 7mm in length.

Symptoms

The maggots of this fly form communal mines in the leaves. Damaged areas at first appear as large, pale green blotches which soon dry up and become brown and papery. This gives the foliage the appearance of having been scorched.  Parsnips, celeriac, parsley, lovage and related wild flowers are similarly damaged by this insect.

There are at least two generations during the year and mining occurs between early May and the autumn. The first generation is generally less numerous than the second, but it can cause a serious check to growth. This may result in small celery plants with a bitter taste. When the grubs have finished feeding, some pupate in the mines while others pupate in the soil.

Control

Non-pesticide control

• Some damage can be tolerated
• Growing the plants under insect proof mesh will prevent female flies laying eggs on the foliage. Crop rotation must be practised in conjunction with this method, otherwise adult flies may emerge from overwintered pupae in the soil and be trapped under the netting
• Susceptible plants can be checked regularly during the summer for early signs of damage
• Infestations that start late in the growing season are unlikely to cause serious harm and control measures may not be necessary at that time
• On uncovered plants control is limited to pinching out infested parts of the leaves
• Burn or bury deeply infested leaves at the end of the growing season to destroy some of the overwintering pupae

Pesticide control

• There are no home garden pesticides that are likely to give control of leafminers