Identification of Invasive and
Reemerging Pests on Hazelnuts
V.M. Walton, U. Chambers, A. Dreves, D.J. Bruck, and J. Olsen
Hazelnuts are produced in many countries, including the United
States. Hazelnuts are grown on approximately 30,000 acres in the
Willamette Valley, accounting for about 99 percent of U.S. production
and 5 percent of world production. Turkey produces more than
70 percent of total world hazelnut production.
Hazelnut species that occur naturally in the Willamette Valley
include the wild native hazelnut, which is found in uncultivated
woodland areas as well as in some parks. Wild and cultivated hazelnuts
are attacked by similar pests.
This publication is intended to increase producer awareness of
important pests that occur in hazelnut orchards in the Pacific Northwest.
The biggest threat to hazelnut production since the 1970s has
been Eastern filbert blight. This disease is found in two-thirds of the
Willamette Valley and, if not controlled, can kill mature trees.
The key insect pests currently associated with hazelnuts include
filbertworm, Cydia latiferreana (Figures 1 and 3); filbert weevil, Curculio
occidentalis (Figure 3); filbert aphid, Myzocallis coryli (Figure 4);
hazelnut aphid, Corylobium avellanae (Figures 4 and 5); filbert leafroller,
Archips rosanus; and obliquebanded leafroller (OBLR, Choristoneura
rosaceana). Of these, filbertworm and filbert aphid are perceived to be
the most important.
EM 8946-E • December 2007
Vaughn M. Walton, assistant professor and
horticultural entomologist; Ute Chambers,
postdoctoral research scholar (horticulture);
and Amy Dreves, Extension entomologist, all of
Oregon State University; Denny J. Bruck, research
entomologist,, USDA-ARS Horticultural Crops
Research Laboratory, Corvallis, OR; and Jeff
Olsen, Extension faculty (horticulture), Yamhill
County, Oregon State University.
Figure 1. Adult filbertworm (photo courtesy of USDA
Forest Service).
2
Filbertworm and filbert weevil
Filbertworm and filbert weevil larvae
feed on nut kernels and can cause between
20 and 50 percent damage if untreated.
Both species cause similar damage
(Figure 2). Infested nuts have holes in the
shell, and the kernels are damaged by feed-
ing and contaminated with feces.
Filbertworm and filbert weevil popula-
tions also infest several oak species and
wild hazelnut stands. These populations
can migrate to nearby hazelnut orchards
and cause crop loss.
Identification
Filbertworm larvae are creamy to pink
and approximately ½ inch long (Figure 3).
They have three pairs of true legs and addi-
tional pairs of prolegs toward the posterior
portion of the body. After emerging from
nuts, larvae defend themselves by regur-
gitating a red excretion and moving rela-
tively fast.
Filbert weevil larvae are similar in
length, but are grublike and creamy col-
ored (Figure 3). Larvae are rather inactive
when touched and curl in a c-shape. They
have only three pairs of true legs.
Life cycle
The majority of adult filbertworm
moths (Figure 1) emerge from late June
to early October. They lay eggs near nut
clusters and on leaves close to developing
husks. After hatching, the minute larvae
search for a nut and feed on the part of
the husk that adheres to the nut until they
locate a soft spot through which they can
enter the nut. They may feed in the nut for
several months before reaching maturity.
The mature larvae exit the nut by chew-
ing through the side of the shell or enlarg-
ing the entrance hole. They drop to the soil
beneath the tree and overwinter in organic
material and soil to a depth of 2 inches.
Damage may occur as early as late May,
when nut development begins. Damaged
nuts often drop early.
Figure 3. Filbert weevil larvae (left and right) are more grub-
shaped and creamy colored than filbertworm (center), which has
three pairs of true legs, prolegs, and a darker body color.
Figure 2. Hazelnuts with clearly visible emergence holes made by
filbertworm or filbert weevil.
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Little has been learned about the biology of the filbert weevil since
initial work was done by Dohanian in 1944. Adult weevils cut small
holes in the nut shell and lay eggs in the nut during the early part of the
season (May to June). Larvae hatch and feed on the kernel until they
reach maturity in August. Damage is not observed until the end of the
growing season.
After nuts drop, larvae exit and burrow into the soil to a depth of
3 to 6 inches. Adults emerge in the spring after hibernating as larvae in
the soil for up to 3 years.
Pest status
Studies by Dohanian indicated that roughly 50 percent of infested
nuts are damaged by filbert weevil and 50 percent by filbertworm.
Infested hazelnuts collected in cultivated and abandoned orchards in
2006, however, showed 91 percent filbertworm and 9 percent filbert
weevil. Collections of nuts in several orchards during 2007 did not reveal
filbert weevil infestations.
Filbert aphid and hazelnut aphid
Filbert aphid and hazelnut aphid feed on husks and leaves. Aphid
feeding drains nutrients from leaves and may reduce photosynthesis
due to the growth of black sooty mold on the aphid’s honeydew excre-
tions. It is believed that reduced photosynthesis may result in substantial
crop losses in the long term. It is unknown whether large populations
of aphids feeding on husks can cause premature nut drop and lower nut
quality.
Identification
Often both species are found on a leaf, which makes it easier to dis-
tinguish them (Figure 4).
Filbert aphid has smaller cornicles, which often are not visible to the
naked eye. Cornicles look like tail pipes and are used to excrete honey-
dew. The antennae and legs are the same color as the body.
The hazelnut aphid, on the other hand, is often difficult to see, as it
is greenish and blends in with plant tissue. The cornicles of this species
are longer and more visible. The antennae and legs are darker than the
body.
Pest status
Before the mid-1980s, the filbert aphid was considered the only
important aphid pest of hazelnuts in Oregon. Aphids were controlled
with several sprays of organophosphates each season.
The management of filbert aphid changed after the introduction of
a cool-climate French strain of the braconid parasitoid Trioxys pallidus
between 1984 and 1986. This parasitoid wasp spread rapidly and became
established as a consistent control agent.
Figure 4. Hazelnut aphid (top)
and filbert aphid (bottom).
Cornicle
Cornicle
4
The hazelnut aphid, a newly invasive
species, was first reported by the Oregon
Invasive Species Council in October 2003
on hazelnut trees in the northern Wil-
lamette Valley. Recent collections of this
aphid from various orchards and wild
habitats show that this pest has spread
rapidly into many hazelnut production
areas. However, little is known about the
status of this aphid in hazelnut orchards.
Several management changes have
taken place since the initial release of
T. pallidus. Large aphid populations
on husks have been reported recently,
leading to increased chemical control
efforts by growers. Little is known about
the underlying reasons for increased
aphid activity in hazelnut orchards in the
Pacific Northwest. Sampling was conducted in several orchards in the
Willamette Valley during 2007, and large populations of both species
of aphids were found on leaves. Husks were primarily populated by
hazelnut aphid (Figure 5).
In addition, there have been several reports of poor biological
control. Our data suggest that hazelnut aphid populations on husks
showed low parasitism rates. Collections of mixed aphid species from
different field sites during 2007 indicate parasitism of 15 percent
(n=15,819) on leaves and 2.84 percent (n=3404) on husks. Other
research has found parasitism rates between 11 and 28 percent, resulting
in aphid population reductions of 26 to 48 percent.
Conclusions
Hazelnut producers are continuously confronted with changes in the
insect pest and disease complex. In order to continue the production of
superior quality hazelnuts and remain profitable, producers need to be
aware of the specific pest complex in their production units.
Initial survey work in hazelnut orchards indicates that the focus
should be on monitoring and on alternative and integrated pest control.
“Forgotten pests” such as filbert weevil and hazelnut aphid may be
important. Producers need to be aware of these pests and be willing to
use newly available, environmentally safe control methods. Examples
of such options include entomopathogenic nematodes (nematodes that
prey on insects), mating disruption, and organic compounds. Further
work needs to be done on the biology and ecology of filbert weevil and
hazelnut aphid.
The newly invasive hazelnut aphid may change the current aphid
management protocol in hazelnut orchards. Future work on aphids may
include the preservation of natural enemies of filbert aphid and the
importation of new natural enemies for hazelnut aphid.
Figure 5. Hazelnut aphid feeding on husks and parasitized aphid
mummy (bottom right).
hazelnut aphid
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For more information
OSU Extension Service
Olsen, J. 2002. Growing Hazelnuts in the Pacific Northwest. Oregon
State University Extension Service, EC 1219. Revised July 2002.
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Other publications
AliNiazee, M.T. 1998. Ecology and management of hazelnut pest
management. Ann. Rev. Entomol. 43:395–419.
Bruck, D.J. and V.M. Walton. 2007. Susceptibility of the filbertworm
(Cydia latiferreana, Lepidoptera: Tortricidae) and filbert
weevil (Curculio occidentalis, Coleoptera: Curculionidae) to
entomopathogenic nematodes. J. Inv. Path. 96:93–96.
Dohanian, S.M. 1944. Control of filbertworm and filbert weevil by
orchard sanitation. J. Econ. Entomol. 37:764–766.
Dunning, C.E., T.D. Paine, and R.A. Redak. 2002. Insect–oak
interactions with coast live oak (Quercus agrifolia) and Engelmann
oak (Q. engelmannii) at the acorn and seedling stage. USDA Forest
Service Gen. Tech. Rep. PSW-GTR-184.
El-Haidari, H. 1959. The biology of the filbert aphid, Myzocallis coryli
(Goetze) in the Central Willamette Valley. PhD thesis. Oregon State
University, Corvallis. 71 pp.
© 2007 Oregon State University. This publication may be photocopied in its entirety for noncommercial purposes.
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cooperative program of Oregon State University, the U.S. Department of Agriculture, and Oregon counties.
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Published December 2007.
Filbertworm and filbert weevil
Filbert aphid and hazelnut aphid
Conclusions
For more information
