Ken Johnson, John Pinkerton, Jay W. Pscheidt
Hazelnut trees are susceptible to infection from bud break (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.
