Notes on Stone Fruit Insects &
Mites
Aphids
Identification
Aphids can weaken plants by the removal of sap, which causes leaves to
wilt, curl or yellow. Many spread diseases. They are often found in colonies,
usually on the underside of leaves. They excrete a substance called "honeydew"
that promotes development of black sooty mould on leaf and fruit tissues.
Aphids may be winged or wingless. Winged aphids are associated with migration
from one crop or host plant to another.
Period of activity
Aphids have complex life cycles. In Ontario, many aphid species overwinter
in the egg stage on primary hosts. In the spring, the egg hatches and
produces wingless offspring. These reproduce without mating and give birth
to live young, which produce several generations of wingless females.
When populations develop to high densities or when hosts begin to die
back or mature, winged forms are produced and migrate to secondary hosts.
In the fall, when temperatures drop and day length shortens, or when the
plants slow their growth or die, winged forms are once again produced.
These fly back to primary hosts where they mate, lay eggs and die.
Monitoring and thresholds
Peaches can tolerate infestations of up to 30% of their terminals or
20 colonies per tree. The threshold for control in nectarines is much
lower at 10% terminal infestation or five to 10 colonies per tree. Consider
the presence or absence of predators before you spray. Most growers choose
not to control aphids in bearing trees, except in extreme situations.
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