Beet leaf miner

Beet leaf miner is a fly whose larvae tunnel inside the leaves of beetroot, spinach beet, Swiss chard and some other related plants creating large irregular blotch-shaped mines.

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Beet leaf miner damage
Beet leaf miner damage

Quick facts

Common name Beet leaf miner
Scientific name Pegomya hyoscyami
Plants affected Beetroot, spinach beet, and Swiss chard
Main symptoms Blotchy leaf mines (pale areas) on leaves
Most active April to September

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What is beet leaf miner?

Beet leaf miner adults resemble small house flies. The larvae cause plant damage by tunnelling into leaves of susceptible plants and eating the internal tissues.

The fly belongs to the family Anthomyidae, it is a diverse group of flies with over 100 species Britain.  Whilst a few are leaf miners others feed on roots such as the cabbage root fly. Most do not damage garden plants. More information on this fly family is available from the Anthomyidae recording scheme. 

Nearly 900 other insects, including some beetles, sawflies and moths create leaf mines as larvae more information about some for these insects can be found at The leaf and stem mines of British flies and other insects.
 

Symptoms

Beet leaf miner larvae tunnel inside leaves creating large irregular blotch-shaped mines. The damaged areas may be pale green initially but mined parts of the leaf soon turn brown and shrivel. Early summer damage is potentially the most harmful to the plants as crops may be set back, damage on more mature plants may have less impact although may render leafy crops inedible.

Management

Non-pesticide 

Leaf miners can be part of a healthy balanced garden, most species will have natural enemies including parasitoid wasps. Birds such as blue tits can sometimes open mines to consume the larvae within. On plants where leaves are to be consumed leaf miners can however, be difficult to tolerate.

Growing susceptible plants under insect barrier netting will prevent female flies laying eggs on the foliage. However, crop rotation must be practised otherwise adult flies may emerge from overwintered pupae in the soil and be trapped under the netting.

On uncovered plants  removing mined leaves or squeezing the mined areas to crush the maggots may give some control. A careful search may also reveal the white eggs which are laid in small groups on the underside of leaves. Early summer damage is potentially the most harmful to the plants.
 

Pesticides 

There are no pesticides available to home gardeners that are likely to give good control of beet leaf miner. Pesticide control can have undesirable side effects as it will kil natural enemies and other non-target animals.

Biology

The beet leaf miner has two or three generations between April and September. The females, which resemble small house flies, lay small batches of eggs on the foliage of beetroot, spinach beet and Swiss chard. Larvae feed on internal leaf material and the fully grown larvae go into the soil where they spend the winter as pupae.

See also...

Beetroot

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