Notes on Nut Insects
Codling moth
Identification
Codling moth (Laspeyresia pomonella) is a serious pest in English
walnuts and less of a problem in other walnut species, although severe
infestations may occur in some years. Moths are small, approximately 9
mm long and grey-brown with white lines and dark banding. The larvae are
pinkish white with brown heads and reach 10-12 mm at maturity. Mature
female moths lay eggs on the surface of foliage, twigs and nuts. When
eggs hatch the young larvae crawl to and burrow into nuts at the calyx
end or enter where two nuts contact each other. Once inside the nut, larvae
bore tunnels and expel frass out the opening on the husk surface. Frass
that collects on the surface of the nut husk provides a visual indication
of larval -infestation.
Period of activity
Early season infestations that occur before the developing nut shells
harden, will allow larvae to burrow into the kernel or 'nut meat'. Later
infestations that occur after the developing shell has begun to harden
will restrict larval tunnels to the husk and not the inner kernel. Infestation
by codling moth can cause premature nut drop and may be severe in some
years. Where nuts do not drop prematurely, infested husks can impart off-flavours
to the kernel.
Monitoring
Use pheromone traps to detect the earliest emergence of new adults in
the spring. See Suppliers of Pest Monitoring Equipment and Biological
Control Agents on the OMAFRA website.
Management Notes
Insecticides for codling moth control on walnuts have a similar timing
as cover sprays applied on apples for codling moth control.
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