PLANT PROTECTION 1 – Pests, Diseases and Weeds

PLANT PROTECTION 1 – Pests, Diseases and Weeds
Pest cycle
There is a complete metamorphosis (egg,
caterpillar, pupa and adult) with several overlapping
generations (probably 5-6) each year.
Adult moths lay their eggs on the undersides or on
young stems or fruit. Mature larvae spin a cocoon
usually high in the tree near where it has been
feeding. Life cycle takes about 5 weeks in summer.
Moths which emerge late in the season lay eggs
but except for those which infest quince most of
the larvae which hatch from these eggs die. The
last generation of larvae in late summer and
autumn spin their silken cocoons under bark near
the base of the host tree, in wounds from broken
limbs or on litter on the ground. Late in winter or
early spring dormant larvae pupate; the pupa, at
first yellowish, turns brown then almost black just
before the moth emerges any time from August to
early November depending on temperature.
‘Overwintering’
As larvae in cocoons under bark on the trees, on
mummified fruit and litter on the ground, and in
crevices in the soil. Very cold winters can kill
some carry-over pupae.
Spread
By moths flying, they are not strong fliers. They
may migrate from lightly infested adjacent trees
into susceptible fruit orchards.
Transfer of infested fruit, litter,
Transfer of infested nursery stock.
Possibly also in packing boxes.
.
Conditions favouring
Warm, moist conditions, over-irrigation,
over-fertilizing, severe pruning or other factors
which favour lush tree growth and plenty
food for caterpillars. Moth populations buildup
quickly. These conditions also favour the
brown rot fungus.
The lower development threshold is 7.5 o C.
Hot, dry and windy weather is unfavorable.
Even if a heavy infestation is threatened in
spring, hot summer winds can reduce it.
Twig damage can occur from early spring
through to autumn.
Late-maturing varieties of peaches suffer greater
losses than early varieties.
Populations on other hosts nearby which only
suffer slight damage can cause problems for
peaches and nashi.
.
Fig. 65. Pest cycle of the oriental fruit moth (Grapholita molesta).
94 Insects and allied pests - Lepidoptera (butterflies, moths)