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Spores infect young shoot tips

Ken Johnson, John Pinkerton, Jay W. Pscheidt

Hazelnut trees are susceptible to infection from budbreak (early-March) until dry weather prevails in late spring (usually late-May). Spores of the fungus penetrate juvenile stem tissue just behind the meristem where cell elongation occurs. Neither wounds nor natural openings on hazelnut trees have been shown to serve as sites of entry for this fungus. 

The process of a spore germinating and penetrating the shoot tip occurs faster in warm than in cool weather. A short period of wetness is also required to complete the penetration process.

As vegetative stems mature, they become resistant to infection. This means that the site of susceptibility on a new shoot continually travels outward as shoot tips expand. Chemical control measures must target this expanding shoot tip.

Rain and wind are needed to release spores from cankers and spread them to healthy shoots. Although spores are dispersed throughout the winter and spring, individual spores, once released, do not survive for long periods of time. Thus, spring releases of spores are important, and they occur frequently during the months of March, April, and May.

Buds have broken and shoots are starting to grow. This is the time when hazelnuts are most susceptible to infection by this fungus.
Buds have broken and shoots are starting to grow
Photo by Jay Pscheidt, 1997.
 

 

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Budbreak is when hazelnuts are most susceptible to infection. Spores penetrate immature epidemal cells in the region behind the meristem where cell elongation occurs.
Bud break
Photo by Jay Pscheidt, 1990.
 
 

Using the cultivar Royal and a dose of 1,000,000 spores/ml, the infection rate just behind the meristem is 69% while it is 1% for internodes that have already elongated. Juvenile Stem Tissue
Photo by John Pinkerton.

Spores germinate and infect young shoots after a short wet period.
Germination
Photo by Ken Johnson, 1990.
 

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