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.