May 5, 2015
With the string of warm days that we have been experiencing this week leading into bloom, as well as the amount of fire blight that was around in 2014, I expect that we may be in for a tough year with this disease. I have not yet run the MaryBlyt program for Vermont orchard weather stations, but if you were to trick NEWA by recording yesterday as having bloom in the orchard (most orchards in the Champlain and Connecticut Valleys are at tight cluster), predicted fire blight risk is ‘High’ by Thursday and ‘Extreme’ by Friday and through the weekend. Remember, for blossom infection you need open blossoms (or other wounds, I would avoid pruning right now), heat accumulation significant for bacteria to multiply into an infective population, warm weather during infection, and wetting events. Heavy dew or spray applications may be enough to trigger infection.
First line of defense (after you pruned out all infected wood during the winter) was the copper spray that should have been applied at green tip. In most orchards it is too late to apply copper, except for the highest elevation sites. Do not spray fixed coppers after half-inch green bud stage.
The next step will be to have some streptomycin on-hand to apply within 24 hours of a rain event during bloom (remember, we need open blossoms for infection to occur). Now would be a good time to order your supply.
There is too much to the fire blight disease to discuss in this one notice, please review the pertinent section in the New England Tree Fruit Management Guide if you need a refresher.
We will run Maryblyt later today and I will send updates as the situation plays out.