Pear psylla is a serious
pest of pears in the United States and the Pacific
Northwest. It is crop specific meaning it is a
pest only of pears. The nymphs of the pear psylla
produce honeydew which can cause fruit russetting when
it comes in contact with the fruit itself. Besides
russetting, serious populations of psylla can stunt,
defoliate, and even kill trees. As the varieties
of pears differ, so does their susceptibility to damage
from pear psylla. Psylla can be found in other hosts
such as neighboring cherry or apple orchards, especially
in fall and early winter. However, they cannot
complete their lifecycle or reproduce outside of a pear
orchard.
Pear Psylla in Your
Orchard
Pear Psylla are one of the smaller insects found in an
orchard. To clearly see the majority of the
stages, it is best to use some sort of hand lens or
magnifying glass. The psylla adult is probably the easiest stage to find with
the naked eye. The psylla overwinters as an adult
but can be found in the orchard throughout the year.
It can be easily be found in the spring of the year on
the first warm sunny day. The egg of the psylla is
very hard to see with the naked eye, and is usually laid
in the crevice around the bud pre bloom, and on the
freshest green foliage, post bloom. The nymphs of
the psylla hatch and pass through five instars.
The nymphs produce honeydew, that causes fruit damage
when it comes in contact with the pear itself.
This honeydew can cause a mess on the foliage and the
fruit, and is usually found when you come in contact
with the tree. The picture on the left shows a
pear leaf with freshly hatched psylla just starting to
produce honeydew. The picture on the right shows
an adult psylla, ready to lay eggs.
Pear psylla can be found in the
orchard year around. However, adults begin to lay
eggs in the spring as the weather warms up, and
generations continue
to cycle through until the weather cools down in the
fall.
Pear Psylla Life
Stage
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Egg:
The pear psylla egg is shaped like a grain of rice.
The egg is creamy white when laid, but turns to
yellow/orange as it develops towards hatching.
The first eggs laid in the spring are usually
laid as singles, but as the weather warms and in
the summer generations eggs can be laid in
strings. |
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Nymphs:
The nymphs of the pear psylla pass through five
instars. The first instar is creamy
yellow, and shaped like a long cylinder.
The following instars are larger, flatter, and
more oval than the previous. The third,
fourth, and fifth instars have progressively
larger wing pads. All stages have two
large red eyes. |
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Adult:
Their are two forms of adult pear psylla:
winterform and summerform. The adult
overwinters in the winter form stage. The
winterform is slightly larger, and the wings
have a dark smoky area halfway back, while the
summerform wings are clear except for the veins.
The adult holds its wings roof like over their
abdomen. |
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Life
Cycle
The pear psylla overwinters as a winterform adult.
They begin laying eggs in the spring when the weather is
consistently warm, and as the pear buds begin to swell.
The eggs are deposited around the base of the bud, in
cracks and seams. As buds begin to open, as well
as post bloom, eggs are laid on fresh green tissue,
along midveins of leaves, and on sepals of blossoms.
Adults continue to lay eggs through petal fall.
The long egg laying period produces a wide age range of
first generation nymphs, some may complete their
development before the last have hatched. Adults
of the second generation, summerform adults, lay eggs on
terminals and the nymphs feed on leaves and stems of
tender new growth. The nymph spends most their
lives inside the honeydew drop. The fifth instar
nymph leaves the honeydew before molting into an adult.
There are usually 2 or 3 generations of summerforms
before the winterform generation develops again.
The pear psylla can cause three forms
of damage. The most common is a result of the
honeydew produced by the nymphs. Psylla feed by
sucking juice, called phloem, from the pear tree.
While feeding, the nymph produces honeydew which forms
into a droplet. The honeydew produced can drip or
run onto fruit causing a dark russet spot or streak.
This results in fruit marking and can downgrade the
quality of the fruit. In large numbers psylla can
stunt or defoliate trees and cause fruit to drop.
These symptoms, called psylla shock, are caused by
saliva injected into the tree by the feeding nymphs.
Psylla can also transmit a disease, called pear decline,
through their saliva. Pear decline damages sieve
tubes in the phloem and translocates to the roots and
results in root starvation. Pear decline can eventually
result in tree death, however the severity of the
disease depends on the origin of the rootstock.
Psylla shock and pear decline are usually not a concern
in commercial orchards, as control measures to reduce
psylla russett keep populations in check.
Monitoring
Pear Psylla can be found in your orchard throughout the
growing season. It is important to keep your eye
on populations to prevent them from reaching damaging
levels. Adults can be monitored by jarring them
from the limbs onto a beating tray. Hold your
beating tray below a horizontal branch and slap the
limb, adults fall onto the tray and can be counted.
To monitor eggs and nymphs it is best to use a hand
lens. Eggs and nymphs are usually found on shoots
and spurs. Randomly gather several shoots from the
orchard and inspect them for eggs and nymphs. Pear
psylla monitoring is one of the
many services G.S. Long's fieldstaff provides. For
more information or to contact a G.S. Long fieldperson
please send us an
email.
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