I’ll keep this short and to the point. In spite of, or rather in keeping with, what I said the other day, fire blight risk is increasing in Vermont orchards. I’m seeing sustained warm, sunny, relatively windless, and dry conditions for the next 5-7 days, with increasing risk of rain as next week starts. The heat is driving the bacterial population to increase pretty rapidly. Warmth suitable for infection is present. Open blossoms are present. The question is whether ot not you a) have fire blight inoculum in or near your orchard and b) whether or not wou’ll get the necessary wetting to cause infection. For the first one, if you’ve ever had any fire blight in the past couple of years, assume that you have inoculum. The population is moving too rapidly to assume otherwise.
For the second, you may want to wait things out until just before a rain on Monday or Tuesday, but what if ypu miss a dew event? Sunday morning looks like there’s potential for some dew, and that’s enough.
Anyone in any stage of bloom, is to get a streptomycin (or pick your organic biocontrol of choice, but I can’t personally vouch for any at this time) spray on sometime between Friday and Sunday morning. Once a blossom is treated, it’s protected, so later is better to ensure you cover the maximum number of blossoms. But don’t wait so late that you miss a good spray window. Strep should be applied 16 oz per acre in sufficient water to get good wetting, amd I recommend Regulaid or another organosilicone wetting agent be included.
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