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Nemasys - a biological control - can be used but the
leatherjacket grubs can best be dealt with by ordinary cultivation
procedures such as digging and hoeing. there are no soil insecticide
treatments available. If the ground is empty of crops - such as is often
the case on allotments, then a black plastic sheet can be laid down
overnight, and the grubs will come to the surface, where they can be
collected and dispensed with.
The adult Cranefly emerges from the soil
in late summer, and soon get to work laying eggs in the soil - sometimes
within a few days of becoming an adult! The eggs hatch into what we know
as leatherjacket - though small at this stage - burrow into the ground
and feed on roots and tubers throughout the autumn. They turn into
'leatherjackets' during late autumn, then overwinter in the ground,
ready to resume feeding on plant roots as soon as the soil warms up in
spring. Damage of the roots occurs and becomes noticeable in April -
May. Whilst they remain underground in the daytime, they sometimes
emerge at night - especially in damp and worm conditions.
Starlings and Blackbirds are happy to
forage about in the borders and vegetable plot seeking out the tasty
morsels we know and loath as leatherjackets!
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