Jay W. Pscheidt, John N. Pinkerton
Eastern Filbert Blight can be spread in a
variety of ways. Spread can be between regions, orchards,
Long distance spread between regions can occur
via the transport of infected nursery stock. For example,
infected ornamental contorted filberts, Corylus avellana
var. contorta, have been found from Corvallis to Eugene
and even in Pendleton, OR. All of these trees originated
from nurseries located in the heavily infected regions
near Portland. We believe that this was the way EFB may
have been originally introduced into the Pacific
Northwest from the East Coast.
Hazelnut growers need to be concerned about this type
of spread since it can also happen with orchard stock.
There was a situation near Salem where a grower
discovered two trees infected with EFB in a newly planted
hazelnut orchard. It was suspected that the trees were
infected in the nursery before shipment. Early detection,
quick scouting and tree removal on the part of many
people helped eradicate EFB from that orchard.
Quarantines are used to help prevent this type of
spread. Although not perfect, quarantines against
shipment from the East Coast did keep EFB out of our
western hazelnut growing areas for almost a century.
Quarantines have also been imposed within Oregon to
prevent movement of nursery stock from the northern
Willamette Valley to the mid and southern valley areas.
However, some shipments of infected stock still
continued. In December of 1995 the Oregon Department of
Agriculture, working cooperatively with the nursery and
hazelnut industries, imposed a five-year moratorium on
retail and landscape sales of all Corylus in Oregon to
prevent the spread of EFB. Corylus stock cannot be moved
from infected areas (north of Woodburn and McMinnville)
to uninfected areas. The moratorium does not affect
shipments out of Oregon.
Spread between orchards has been a hotly debated
topic since EFB was first discovered in the Willamette
Valley. Before we knew much about the biology of the
fungus, there was a lot of speculation about movement of
EFB in nuts, nut bins, debris on harvesters, or by birds.
Nuts are not a source of EFB and thus movement of them
does not pose a risk to the industry. Twigs with cankers
can be moved long distances if accidentally transported
in harvest bins or on orchard equipment. Debris from nut
bins should be disposed of by burning or burying. Farm
implements should be inspected and cleaned before
transport from infected to clean orchards.
The bird theory is a favorite among growers who have
observed the habits of crows and blue jays within and
between orchards. There is only circumstantial evidence
to support or deny any bird involvement with this
disease. Small twigs infected with EFB have been observed
in a water basin (part of a meteorological station) at
the Vancouver, WA experiment station. Birds were also
observed to use this basin as a birdbath. If birds do
transport infected twigs, it would likely be for nesting
material and thus would not be transported far. Songbirds
set up small (1 acre) territories during the spring
nesting season. In addition, blue jays generally nest in
conifers. Movement of EFB spores via bird feet is
considered highly unlikely if not impossible.
The fungus is perfectly capable of spreading on its
own without help from man or animals. An EFB spore is
about 10 times smaller than a hazelnut pollen grain. The
spores can become airborne by wind during periods of
rain. From 1989 to 1992, 1 year-old trap trees were
planted from 10 to 150 meters (about 500 feet) upwind of
an infected orchard to see how far spores might travel
once airborne. The number of infected trees found at 10
meters was not significantly different than the number of
trees found at 150 meters. These data indicate that EFB
spores can be moved from infected areas by wind and
remain infective until they land on other hazelnut
The potential for spread is great within an
orchard. Spores are ejected into the wind after cankers
are wet for as little as 5 hours. There may be some
spores that are rain splashed onto neighboring trees or
washed down the scaffolding to growing shoots or suckers
along the trunk. Most of the spores, however, are by
forcibly ejected (squirted) out of the perithcium.
Patterns of diseased trees within an orchard show that
most local spread of the disease occurs to the northeast.
Many of the rainstorms that occur during the spring move
from the southwest to the northeast. This has been a
fortunate characteristic of this disease since the
epidemic began in the northeast part of our growing area.
The spread of the disease into our southern production
areas has been slowed greatly by these prevailing wind
An infared picture of an
infected hazelnut orchard. The white X symbol indicated
where infected trees were first found. The blue diamonds
indicated where infected trees were found the following
year and the yellow boxes indicate where trees were found
the year after that. Note the pie shaped pattern of
spread which is to the north-east along with the
prevailing storm track.
Photo by John
Eastern filbert blight on the
ornamental contorted filbert.
Photo by Jay
From 1989 to 1992, 1 year-old trap
trees were planted from 10 to 150 meters (about 500 feet)
upwind of an infected orchard to see how far spores might
travel once airborne. The number of infected trees found at
10 meters was not significantly different than the number of
trees found at 150 meters. These data indicate that EFB
spores can be moved from infected areas by wind and remain
infective until they land on other hazelnut