Notes on Apple Insects
Aphid
Identification
Three species of aphids are pests in Ontario apple orchards: green apple
aphid (GAA), rosy apple aphid (RAA) and woolly apple aphid (WAA). Aphids
are small (1.5-3.5 mm), soft-bodied, pear-shaped insects that can be distinguished
from other similar insects by the presence of small tubes or tailpipes
called cornicles at the posterior end of their bodies. They use their
long, thin mouthparts to pierce the plants and suck out fluids. When aphids
feed, it results in wilted, curled and yellowed leaves and potentially
malformed fruit. Aphids secrete a substance called honeydew that promotes
the development of black sooty mould on leaf and fruit tissues.
Period of activity
Aphids overwinter as eggs on trees, and the nymphs become active from
petal fall through August. There are multiple, overlapping generations
per year. Female aphids reproduce asexually and give birth to live young,
so populations can increase quickly under optimal conditions.
Monitoring and thresholds
GAA and RAA form colonies on the undersides of leaves on lush terminals
or water sprouts. Thresholds vary depending on the type of aphid present
but established trees can tolerate moderate to high levels of infestation
without loss of vigour or production.
To scout for GAA, examine 10 terminals on 10 trees throughout the orchard.
Green apple aphids are yellow-green in colour with black cornicles. Treatment
is warranted when more than 20% of terminals have active colonies present.
For rosy apple aphids, examine 10 fruit clusters from each of 10 trees
for the presence of aphids and predators. Rosy apple aphids are rosy-brown
or purple and have a white dusty appearance. A fruit cluster is considered
infested if more than 20 aphids are present. Control is recommended if
more than 10% of the fruit clusters are infested.
Woolly apple aphids are rosy coloured with a thick waxy coating and colonies
appear as a cottony mass. Woolly apple aphids feed on suckers, pruning
wounds and tree roots. Root feeding results in the formation of galls.
Currently there are no thresholds for WAA.
Management notes
The waxy protective coating on woolly apple aphids makes chemical control
difficult. As a result, good coverage is necessary for insecticides to
be effective.
Natural enemies include lacewings, ladybird beetles, pirate bugs, syrphid
flies, predatory midge larvae and parasitic wasps, which often keep aphid
populations low. The presence of beneficial insects may delay or prevent
the need for insecticide applications. Beneficial insects should be noted
when monitoring a crop. The use of broad-spectrum insecticides often has
serious negative impacts on beneficial insects and mites.
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