Do you think we can help my sickly Harry Lauder's
walking stick? He is about 10 years old and until now has never had
a sick day, but is getting some foliage loss which is not typical
for the poor fellow.
What should we do? Some of the
reading I have done has said this is a disease that can be
controlled with some extensive pruning. Do
you think this is worth a try? - J.K. -
A blight
Eastern filbert blight (Anisogramma anomala) is a
fungal disease that's native to eastern North America, where it is
occasionally a minor nuisance on American hazel (Corylus
americana). On these shrubby native trees it may weaken or
kill some branches but generally does little more than that and
seems to affect only otherwise weakened wood.
However, eastern filbert blight is lethal for even a well-grown
European filbert (Corylus avellana). This is the species
that gives us not only the standard nut producing trees but the
shrub variously called twisted filbert, contorted hazel or
Harry Lauder's walking stick in tribute to a vaudevillian actor's
trademark cane. Another susceptible Corylus species is the
Turkish filbert (C. corluna), being used here and there in
North America as a pyramidal, drought tolerant street tree.
A battle
We first met eastern filbert blight 40 years ago and decided
then that we would not grow the shrub anymore, attractive though it
can be. The work required to keep the disease at bay just wasn't
worth it for us. About the same time, the disease was jumping the
continental divide and beginning to plague formerly clean Pacific
Northwest nut farms. It's still a pitched battle today, and no
cure, prevention or highly resistant variety has been developed
even for the nut growers, despite much incentive to stave off this
devastating disease, and much effort.
If there is a breakthrough in nut orchards, growers of the
ornamental filbert will certainly apply it but for now they
continue as before, doing the extra work to keep a crop clean until
the plants reach sale size.
All this means we gardeners continue to have these shrubs as
only temporary residents. Infection is just a matter of time, after
which the plant has 4 to 10 years even if given special care.
On your toes year-round to
control eastern filbert blight (EFB):
Winter:
Inspect the hazel or filbert carefully in winter for dead and
dying branches. You're looking then for the earliest telltale on
the wood, distinctive rows of small elliptical eruptions. These
become rows of football shaped cankers on any branch that survives
the early infection.
Prune out everything dead or suspicious, cutting 2 to 3 feet
below the lowest symptom since the spread is outwardly invisible
and does extend that far. Clean your pruning blades with rubbing
alcohol after each cut, and burn the wood or chip it small enough
that all bits dry completely, quickly -- otherwise the spores live
on in moist dead wood.
Right: Can you tell cankered wood from clean? Look at the
honey colored, smooth new branch upper left in this composite
photo. Now look at older branches such as the inset, upper right in
this composite. There the bark is not smooth but has rows of
eruptions -- wounds called cankers. Then see that there is also
dead wood with cankers that are even larger but in the same regular
rows (inset lower right).
Spring:
In spring, as buds break and for about 8 weeks thereafter, prune
out any new shoot that wilts or fails to thrive. (It's a
watchword of all blights, that infected new growth darkens and dies
suddenly as if it's been targeted by an evil spell.)
You can also give all the new shoots some protection from new
infection with a fungicide or fungus barrier such as an oil
or anti-transpirant. If you use a fungicide, do not use the
same product for each of the three to four applications. Switch
between a copper-based Bordeaux mix and a horticultural oil, for
instance.
Summer:
In mid and late summer, look closely at any branch with wilted
or discolored leaves. Prune as in winter.
All the while, maintain excellent growing conditions for the
plant and control other problems to avoid the stress that can
increase susceptibility.
What are the best growing conditions? C. avellana is an
understory species that appreciates cool air, midday shade, and
loose, rich, loamy soil.
Below: Signs that this shrub has an additional problem, an
insect infestation. It's probably alder lace bug (Corythucha
pergandei). If you decide to give blight control a try, you
must also stay on top of any such insect pests to lessen
stress.
Tough regimen for
the home gardener
The gardener faces four hurdles in implementing Eastern filbert
blight controls.
One, we don't usually recognize the signs until
the infection's too far gone. We don't look so closely at our
plants as a professional grower does or we don't realize we should.
The infection gives no distinct outward sign in its first year
unless some new growth wilts and dies, and we're likely to consider
that normal garden wear and tear. The late summer eruptions that
are the first indisputable sign are small and may escape notice yet
the affected wood must be removed right away before it can spread
spores the next spring.
Two, we have few, if any, fungicides available
to us and hiring a professional to make the application is not a
simple or inexpensive thing. (Personally, we are glad that
fungicides have been greatly restricted because most provide too
little to offset the risk they present to people and environments.
Professionally, we recognize how this limits our disease management
options. However, in accepting the challenge to operate in other
ways we have been favorably impressed with alternatives, from
resistant varieties to betterment of growing conditions.)
Three, effective pruning will remove so much
wood that when we're done the shrub may have very little ornamental
value.
Four, many gardeners favor prominent
placement for this shrub with solid background to show off its
branches. That means it's often in the open or near a solid wall.
The first position denies it the cool air and midday shade that's
most healthful for this species. The second puts it at risk from
reflected heat in summer and larger, more damaging temperature
shifts in winter.
More about eastern filbert blight
From Cornell University
plantclinic.cornell.edu/factsheets/filbertblight.pdf
(If link fails, copy the line above to your browser bar to
download the bulletin)
"The first symptoms to appear on infected trees are elliptical
black stromata. They are formed in longitudinal rows on infected
branches… usually between May and August… 12-18 months after the
initial infection."
From Michigan State University
http://msue.anr.msu.edu/news/eastern_filbert_blight_on_turkish_filbert
"…will produce football-shaped stromata on new shoots (Photo 1).
Later symptoms of filbert blight on Turkish filbert include branch
dieback (Photo 2) and orange cankers on branches (Photo 3)"
From Oregon State University
http://oregonstate.edu/dept/botany/epp/EFB/
"Fungicides are best used to protect susceptible tissue in the
spring at bud break and for the next 8 weeks. …additional
applications have not resulted in significantly better disease
control. …Alternating fungicides with different modes of action has
been effective to manage EFB."
From Canada's Ministry of Agriculture
http://www.agf.gov.bc.ca/cropprot/filbertblight.htm
"In coastal (British Columbia), the spray period will generally
be from late March until early May. The fungicides registered for
EFB can only protect young shoots from initial infection, i.e. they
need to be applied before the fungal spores land on vulnerable
young tissues… The following fungicides are registered for EFB in
Canada…"
From Purdue University
www.ppdl.purdue.edu/ppdl/weeklypics/12-19-11.html
"…difficult to control… fungicides …impractical in the home
landscape. Pruning to remove the cankers …often requires removal of
so many branches that the ornamental value of the tree is lost.
…There are several resistant varieties of nut-bearing filberts but
so far no resistant types of contorted filbert."