The Ontario Fire Blight Risk Maps are predicting high to extreme infection risk this week across the province. Later regions are still in bloom. Early regions should watch for rattail bloom in any blocks that are in petal fall.
Growers should keep a protective program until the risk drops back down below high. Windy days and increasing pollinator activity this week will have moved bacteria to open blossoms, particularly if fire blight has been an issue in the orchard or neighbourhood.
While large amounts of rain are not necessarily predicted until end of the week, sporadic showers can occur. Of more significant concern, however, is the development of dew. With the warm days followed by cooler nights, dew can form. This moisture is enough to wash bacteria into the open bloom.
Bacteria will have multiplied rapidly with the very warm temperatures. Antibiotics applied earlier this week will not protect any new blooms that have since opened. These products also break down rapidly in high UV, giving protection for only 1-2 days.
Infection will occur with any wetting event if a protectant program is not in place under high to extreme risk conditions. Under extreme risk, even orchards that did not have fire blight last year are likely to see infection.