| |
Apple Scab
The apple scab fungus survives winter on fallen leaves
on the orchard floor. These leaves are the source of spores
which cause primary infection the following spring.
Anthracnose
September, October and November is thought to be the most
important period for the release of rain-splashed spores
(conidia) from existing cankers. These spores can directly
penetrate healthy bark tissue, causing infection and development
of multiple lesions which are usually not seen until the
following spring. Although the canker has attained full size
by this time of the year, the fungus can live for several
years in the bark, producing spores each fall for new infections.
In addition, old bark if left within the canker can also
produce ascospores, which are not dependent on water for
transport. This spore type can be spread by wind and is most
likely responsible for spread of the disease over greater
distances. The importance and role of this spore type as
a mechanism for effective spread and subsequent infection
is not clearly understood at this time. |
Closeup of mature, spore producing
Anthracnose canker. |
Apple scab
Scouting at this time of the year is not useful for apple
scab, but the following steps can be taken to reduce the
potential for disease carryover to the next season:
- Within 30 days of leaf fall, rake apple
leaves into the middles and shred them.
- Shredding may prevent the overwintering
scab structure (pseudothecia) from forming and promotes
more rapid decomposition by microbes.
- Urea applications are also helpful to
soften leaf tissue and promote more rapid decomposition
by microbes.
Anthracnose
As
mentioned in the previous section, early August is the
critical time to walk through the orchard and remove:
- dead bark from within existing cankers and
- small cankered branches.
If you delay this sanitation tactic until after harvest,
a significant amount of infection from rain-splashed spores
is likely to have already occurred. Partial control has been
observed with the use of two copper sprays prior to fall
rains (September and October) and a single application in
the late winter (early February). An integrated program including
well-timed canker removal and timely application of fungicides
will likely be most successful in the long run, but at this
time, the laborious process of scouting and late summer canker
removal is the cornerstone of anthracnose control. |
