The effectiveness of winter treatments with copper or lime sulphur to control Sooty Blotch on apple.

Summary

In 2002 and 2003 two randomized trials and three “on farm” trials where carried out
to test the hypothesis that a single winter treatment could reduce the primary
inoculum of Sooty Blotch sufficiently to prevent fruit disease during summer.
copperoxychloride (0.2%-0.4%) and lime sulfur (4.0%-5.0%) were applied until run-off
in March shortly before bud break. Assessments of Sooty Blotch incidence and
severity where made immediately after harvest.
The winter treatments with copperoxychloride did reduce disease severity during
summer in one case. The treatments with lime sulfur reduced the disease level in
three sites to some extent. However, winter treatments alone were not nearly as
efficient as summer treatments. Therefore, we see no reason to advise this kind of
treatment with lime sulfur in practice as the effectiveness is poor, the necessary
spray cover can not be reached under practical conditions, and with the amount of
material needed for this single spray five sprays can be made in summer that will be
more effective to control the disease.