time it takes from a spore infecting a hazelnut shoot to
the time we begin to see a canker symptom is called the
latent period. This latent period is very long for EFB
and is generally considered to be 15 months. However, it
can be much longer before we see symptoms. The experiment
described below outlines the problem.
A total of 30, healthy 2-year old hazelnut trees were
placed at five sites within a diseased orchard in the
spring of 1988. These trees were replaced with 30 more
healthy trees each week. After one week of exposure,
trees were taken to a clean holding site for several
months to allow symptoms to develop. A total of 120 trees
were exposed during that spring.
A total of 63 trees or 30% became infected and showed
typical EFB cankers in June of 1989. These trees were
destroyed before spores could infect the other trees. The
remaining trees were held an additional year at this
clean holding area.
A total of 16 more trees developed typical EFB cankers
in June of 1990, about 26 months after exposure. This
means it may take up to three growing seasons (two years)
after infection before symptoms of EFB are seen.
There is one other requirement before cankers form. An
extended cold period, during which the tree undergoes
dormancy, is necessary to initiate formation of