This means that if you had a problem with scab last year, you should be ready for the early scab infection periods. It is important to avoid early infections on sepals, as these are difficult to detect and can provide conidial inoculum throughout the early part of the growing season. Survival of overwintering powdery mildew should be moderate to high in the absence of prolonged cold temperatures. If weather conditions are favorable for mildew in 2001, the abundance of inoculum could lead to high levels of this disease, especially on mildew-susceptible cultivars. Fire blight bacteria overwinter in cankers, or at the ends of pruning cuts where blight was cut, from the previous season.
Cold temperatures can decrease the amount of overwintering inoculum.
In warmer areas, bacteria have been detected from both kinds of cankers. Look for apple scab ascospores to mature near the green tip stage of bud development. It is important to avoid early infections on sepals, as these are difficult to detect and can provide conidial inoculum throughout the early part of the growing season. Although this spray does not eliminate the possibility that fire blight could become epidemic in 2001, in some years it may reduce considerably the amount of inoculum available for blossom infections. This dormant application is recommended where fire blight was present in 2000 and on young trees of susceptible apple cultivars such as Gala, Fuji, Braeburn, Pink Lady, Ginger Gold, York, Jonathan, and Rome Beauty, or on any cultivar on M.9, Mark, and M.26 rootstock.