Eastern filbert blight

Anisogramma anomala

Symptoms include the formation of cankers on twigs. It is a particular problem on Corylus avellana, which is farmed commercially. It is native to North America. The spores are spread by rain splash. Fungicides can be used to control the disease.

Symptoms and Signs 
The first symptoms to appear on infected trees are elliptical black stromata. They are formed in longitudinal rows on infected branches, and appear only after extended cold periods, usually between May and August. The first stromata to appear erupt from branches 12-18 months after the initial infection. The infected area is known as a canker, and these cankers are perennial, adding both additional rows and more stromata to existing rows each year. On European Hazelnut, these cankers can expand from a few centimeters up to 1 meter annually; on American Hazelnut they increase by only 1-10 centimeters in the same amount of time. Infected branches become girdled. Leaves on these branches die, remain attached, and flag the presence of the disease during the summer months. The tree declines, with many leafless, dead, and dying branches visible in the canopy. If no action is taken, in 5-12 years time the tree will be dead. 

Disease Cycle 
New infections are initiated in the spring, when spores land on the new tissue immediately adjacent to the apical meristems of growing shoots. European Hazelnuts are most susceptible during the period that new shoots are actively elongating and sending out young leaves. Once spores have adhered to the stem surface, they penetrate epidermal cells directly. Wounding and natural openings are not thought to be important to the establishment of the fungus. Infection is facilitated by extended periods of high humidity, but occurs over a wide range of temperatures. 
After entering the tree, the fungus invades the phloem and outermost layers of xylem and grows extensively. Twelve to eighteen months later, stromata erupt from the surface of the branch. Within are perithecia, or flask shaped reproductive structures. Ascospores are formed in sacs within the perithecia. The following spring, the spores are shot out from the perithecia, sometimes collecting in a milky ooze on their surface. Wind, wind-driven rain, and splashing raindrops spread the disease to other branches and to nearby trees.

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