Hazelnut, Filbert (Corylus)
Plant Health Problems
Diseases caused by Fungi:
Eastern filbert blight, Anisogramma anomala.
Native filberts serve as a host and have some resistance to this disease
but European filberts are seriously affected. The fungus attacks new twigs and
then moves into large limbs, and forms cankers that can kill the entire tree.
The fungus breaks through the dead bark in linear rows and forms distinctive
slits consisting of dark lumps of fungal tissue where the spores are formed.
Prune and remove infected wood as soon as possible. Fertilize trees in the
spring and water well during drought to maintain tree vigor. Since this disease
is usually not a serious problem for the health of the trees, chemical controls
are usually not necessary.
Diseases caused by Bacteria:
Filbert bacterial blight, Xanthomonas corylina.
The pathogen causes small angular or irregularly circular, pale
yellowish-green, water-soaked lesions in the leaf blades. Later the lesions
turn reddish-brown. Lesions are often grouped together near the tip of the leaf
where water accumulates, and then grow down into the twigs. Twigs, branches, and
trunks can be girdled by the infection and young trees usually die. Older trees
may survive, but fail to produce nuts. Bacteria are spread by rain splash and
by pruning tools.
Prune and remove infected twigs and branches as soon as possible. It is important
to prune 6-8" beyond visible symptoms and to disinfest any pruning tools
between cuts (10% household bleach or 70% alcohol). Fertilize trees in the
spring and water well during drought to maintain tree vigor. There are no
effective chemical controls.
Insect Problems:
Aphid, Macrosiphum corlyi.
Aphids infest the leaves of hazel. If control is necessary, acephate,
malathion, or insecticidal soap, which are among the compounds registered for
use against this pest in Connecticut, should be effective. Consult the label
for dosage rates, safety precautions, and preharvest intervals.
Hazel bud gall, Eriophyes asellanae.
This gall, caused by a mite, is common on Corylus americana.
Usually it involves a terminal bud, but sometimes occurs on a lateral bud. Spraying
before the galls form with malathion, which is among the compounds registered
for use against this pest in Connecticut, should be helpful in controlling
these mites. Consult the label for dosage rates, safety precautions, and
preharvest intervals.
Hazelnut weevil, Curculio obtusus.
This is one of the smaller nut weevils, having a length of between 1/4"
and 1/3". It varies in color from ash-gray to brown, and has darker
markings along the top of the wing covers. Weevils appear in June, and the females
deposit eggs in the developing nuts. Infested nuts fall early. There is one
generation each year.
Hazel whitefly, Trialeurodes corlyi.
This whitefly infests the leaves of both Corylus americana and C.
rostratus. It is rarely abundant and control measures probably are usually
unnecessary. Malathion, which is among the compounds registered for control of
this pest in Connecticut, may be used. Consult the label for dosage rates,
safety precautions, and preharvest intervals.