Friday, August 3, 2012

Corkscrew Hazelnut Infected With Eastern Filbert Blight

Corkscrew Hazelnut (Corylus avellana 'Contorta') infected with Eastern Filbert Blight
Photo credit: Kimberley Pacholko
This ornamental corkscrew hazelnut (Corylus avellana 'Contorta') has contracted a lethal disease known as Eastern Filbert Blight. The disease is caused by the fungus - Anisogramma anomola and is native to the northeastern United States and eastern Canada (although it has appeared in British Columbia, as early as 2001). Hazelnuts native to this region (Corylus americana) have proven to be more resistant to the disease (some are even immune) than the imported European hazelnuts (Corylus avellana).

Often one of the first symptoms homeowners report are droopier than normal leaves, accompanied by the dieback of twigs and branches. Dead leaves may remain attached to the branch, this often a good indicator of the disease. Upon closer inspection elongated (football shaped), dark-brown to black fruiting bodies called stromata can be found, appearing in relatively straight rows lengthwise along the branch. The stromata erupt within cankers (dead areas on the bark or stem, often sunken or raised), approximately 12 to 18 months after the area has been infected. The cankers continue to grow, eventually girdling the branch, resulting in branch dieback. (Note: According the Plant Disease Diagnostic Clinic, at Cornell University cankers can grow in size anywhere from a few centimeters up to 1 meter annually.)

In the spring, about the time the hazelnuts are at bud-break, the stromata release fungal spores. These spores are carried by rain and splashing water droplets driven by wind, to new areas of the branch, new branches and potentially new trees of the same species. New rows of stromata are also formed along the margin of the canker each year. (Note: New growth tends to be the most susceptible to new infections.) The following season new stromata will erupt in the infected areas and if not pruned off before bud-break  they too will release their fungal spores, and the cycle continues. Once a branch has died the fungal spores within that branch also die. The fungus requires moisture in order to sporulate, thus diseased branches that have been pruned-out should be burned or shredded to help prevent new infections.

Corkscrew Hazelnut (Corylus avellana 'Contorta') infected with Eastern Filbert Blight
Photo credit: Kimberley Pacholko

Usually for the small home gardener by the time the disease is diagnosed there is not much that can be done, other than to remove and destroy the tree. For larger trees or smaller trees that have been caught early the following treatments may prove helpful in treating and controlling the disease.
  • Prune out and destroy infected wood well below the cankers (1 to 3 feet below). This must be done before bud break in the spring. The branches must be pruned back this far to ensure the complete removal of all fungal spores (which are always ahead of the visual signs of the disease). Like a cancer any remaining spores can continue to grow and kill branches.
  • Plant resistant cultivars 
  • The following fungicides are registered for Eastern Filbert Blight in Canada (The list is from the B.C. Ministry of Agriculture
    1. Copper Oxychloride 50 or Copper Spray at 3.0 to 9.0 kg/ha (1.2 to 3.6 kg/acre) in at least 1,000 L/ha (400 L/acre) of water. Use the low rate on small trees and the high rate on mature trees. Do not apply within1 day of harvest. Note: Copper is generally acceptable for organic production. Check with your certifying agency.
    2. Flint 50 WG (50% trifloxystrobin) at 140 to 280 g/ha (56 to 112 g/acre) in at least 1,000 L/ha (400 L/acre) of water. Use the higher rate when disease pressure is severe. Do not apply more than 4 times per season. Do not apply more than two consecutive applications of Flint. Do not apply within 60 days of harvest.
    3. Quadris Flowable (250 g/L azoxystrobin) at 900 mL/ha (360 mL/acre). For mature trees, use at least 1,000 L/ha (400 L/acre) of water. Do not apply more than 4 times per season. Do not apply more that two consecutive applications of Quadris. Do not apply within 45 days of harvest.
Note: For Ontario residents check the Ontario Ministry of the Environment for an up-to-date list of permitted pesticides.

Look-like Diseases:
According to Jay W. Pscheidt, Extension Plant Pathologist at the Oregon State University, Eastern Filbert Blight resembles another fungal disease caused by the fungus Eutypella cerviculata. Eutypella produces similar spore producing structures, however, they are said to be smaller in size and produced on dead wood. To properly identify this fungus, take a small knife and scrap away the surface layers of the diseased area. If the disease is the result of the fungus Eutypella cerviculata  rather than EFB  you will find black rings around the stromata.

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