Leaf miners

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					Leaf miners                                                                                            GWF245
                                                                                           Updated January 2009

Wiggly lines or blisters on leaves are tell-tale signs of a leaf-miner attack. There are many
different species but the damage is rarely serious enough to warrant any action.

Q What are leaf miners?                fly. Its larvae tunnel into            turn into blotches. Unlike the
                                       beetroot-family plants like            other leaf miners there is only
A Many insect larvae produce           spinach, and weeds, such as fat        one generation per year. They
mines by burrowing, and feeding        hen. It lays up to 20 eggs in spring   overwinter in the mines, so it is
between the upper and lower leaf       and early summer. The white            worth picking off infested leaves
surfaces. This lets in air, so mines   larvae or maggots feed for about       on precious plants.
are often pale or silvery. Mines       two weeks making pale leaf                 Lilac-leaf miner (Caloptilia
vary in shape from wiggly lines to     blisters. They pupate in the soil      syringella) lays eggs on the leaf
blisters according to the miner        for 2-3 weeks. The pupae from          undersides of lilacs, ash and
involved. Affected plants look         the last generation overwinter in      privet in late spring and early
bad, but the long-term damage is       the soil. Like celery fly, there are   summer. The caterpillars hatch
usually slight. There are              up to three generations each           and begin life as leaf miners,
exceptions, though eg if seedlings     summer. The later ones can be          blistering the leaves. As they
are affected, they can die.            very numerous if the late summer       grow, they feed outside the
Q Which species am I likely to         weather is hot and dry. Usually        leaves, inside rolled-up leaves
come across outdoors?                  the damage is only cosmetic and        and webbing. After pupating, the
                                       the plants recover, but you might      second generation of moths
A Celery-leaf miner (Euleia            have to discard some parts, like       emerges in late summer. The
heraclei) often attacks celery,        spinach leaves, for example.           pupae from these overwinter
celeriac and parsnip leaves, and           Apple-leaf-mining moth             beneath trees, hedges and on
less commonly, parsley and             (Lyonetia clerkella) attacks apple,    garden fences.
carrots. Affected plants are           cherries, birch and hawthorn trees         Laburnum leaf miner
stunted and don’t crop well. The       from late spring. When the eggs        (Leucoptera laburnella) lays eggs
tiny, 5mm-long fly lays about 100      hatch, the caterpillars fill the       on the leaf undersides of
eggs inserted into the leaf in         leaves with winding mines, until       laburnums in late spring and early
spring and early summer. They          the fully grown green caterpillar      summer. These hatch into leaf-
hatch in 1-2 weeks. After 2-3          pupates. The chrysalids are            mining caterpillars that bore
weeks burrowing in the leaves the      formed in the foliage in a mass of     spiral mines in the leaves, until
larvae pupate. The pupae may be        webbing. There may be several          the whole mine is a single blotch.
in the leaf or the soil. The second    generations per year. The damage       A second generation emerges
generation of adults emerges 3-4       can look spectacular, but, with        during late summer which feeds
weeks later, and this can be           the exception of young trees, it       until early autumn, when it
followed with a third generation       does no real long-term damage.         produces the cocoons that
in late summer. It survives the            Holly-leaf miner (Phytomyza        overwinter in the fallen leaves or
winter as pupae in the soil. As        ilicis) can attack most hollies. The   on the twigs.
the second and third generations       tiny fly emerges in late spring and
overlap, attacks can be expected
                                                                              Q What are the common
                                       lays eggs in slits beneath the leaf.
at any time during the summer.                                                greenhouse ones?
                                       The larvae or maggots disfigure
    Beet-leaf miner (Pegomya           the leaves with yellow or brown        A Chrysanthemum-leaf miner
hyoscyami) is a small, 6mm-long        meandering mines that eventually       (Chromatomyia syngenesiae), a
3mm-long fly, is a common
                                      Q What do they look like?              Q Can they be sprayed?
chrysanthemum pest also found
on related plants such as             A Although the damage they             A Contact insecticides containing
cinerarias, lettuce, and              cause is obvious, the adults           bifenthrin or pyrethrins may help
groundsel. The adult fly lays its     themselves are inconspicuous           control leaf miners. Don’t spray if
eggs inside the leaf. The             flies, beetles or moths. Gardeners     you are using biological controls.
puncture marks could be               seldom notice them, and
mistaken for the early stages of      identification is a job for experts.
white rust, and eggs, laid in                                                Q What should organic growers
about 10 per cent of them, hatch                                             use?
into larvae after a week. The         Q How do I know if they
larvae produce thin mines             are present?                           A Organic insecticides might give
wandering over the leaves. These      A The mines can wander                 some control, if applied in the
                                                                             early stages of an attack. Using
take about ten days to mature.        aimlessly about the leaf, spiralling
                                                                             fleece or insect-proof mesh over
Several mines together on a leaf      round the leaves or look like
                                                                             celery and parsley, for example,
looks like one large blotch. This     blotches. The miners’ black
                                                                             will keep off celery fly, as well as
resembles the damage caused by        droppings can be seen in the
                                                                             greenfly and carrot fly. In
chrysanthemum-blotch miner            mines. When the mines are small
                                                                             greenhouses, consider using a
(Trypeta zoe), this causes blister-   they are hard to see, but they
                                                                             biological control.
like mines. Affected leaves           rapidly get larger. When fully
wither and die. After pupating as     developed, the whole leaf is
a white blister beneath the leaf,     brown and dead. The miner can
the adult fly hatches and lays        usually be seen as a dark patch in
                                                                             Q Tell me about biological
about 75 eggs during its 2-3-week                                            controls.
                                      the mine. When you open up the
lifetime. Summer is the usual         patch, it turns out to be a grub,      A Greenhouse leaf miners can be
time for attacks, but in a heated     caterpillar or pupa.                   controlled by the parasitic wasp
greenhouse they occur at any                                                 Diglyphus isaea. This wasp thrives
time. Tomato-leaf miner                                                      in summer, and can quickly
(Liriomyza bryoniae) is a tiny,       Q Can they be mistaken for             eliminate leaf miners in
3mm-long, black fly, similar to       anything else?                         greenhouses or conservatories.
the chrysanthemum-leaf miner,
but pupates outside the leaf.
                                      A Eelworms will produce                Supplies can be obtained from
                                                                             Biowise 01798 867574
                                      darkened leaf areas, but there are
                                                                             Defenders 01233 813121
                                      no mines or miners.
                                                                             Harrod Horticultural
Q Are there any others I should                                              0845 402 5300
be on the lookout for?                                                       Just Green 01621 785088
                                      Q What can I do about leaf
A Imported plants, especially         miners?
                                                                             Scarletts 01206 240466
chrysanthemum cuttings, can
carry the South American leaf
                                      A Discourage them by getting rid
miner (Liriomyza huidobrensis),       of weeds that they feed on.            Q Can they be trapped?
                                      Compost or burn infested foliage.
American serpentine leaf miner                                               A Sticky yellow traps used for
(Liriomyza trifolii), American        Prevent further attacks by
                                                                             whitefly control will catch many
vegetable-leaf miner (Liriomyza       squashing the leaf miner as soon
                                                                             adult greenhouse leaf-miner
Sativae) and the North American       as the mines are seen. Picking off
                                                                             moths and flies. They are hard to
cabbage-leaf miner (Liriomyza         affected leaves and destroying
                                                                             recognise, and look like tiny flies.
brassicae). None of these are         them will also help. Digging the
established in the UK, and            affected sites may bury any pests
                                      overwintering in the soil, either
stringent quarantine measures
                                      preventing them reaching the
                                                                             Q Can leaf miners be avoided?
are taken to keep them from
getting into the country.             surface or exposing them to birds      A Sadly, they are so mobile that
                                      and other predators.                   there seems to be no way to
                                                                             avoid these pests.
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