Fire blight risk

May 15, 2015

by Terence Bradshaw

With all credit to Dan Cooley from UMASS, I am sending along a comment of his for Massachusetts growers that is equally pertinent to Vermont:

Fire Blight update May 15 – it’s not done quite yet

With the refreshingly cool weather, the tendency is to think fire blight is no longer an issue and worry about the potential for a major scab infection. But fire blight risk remains high into early next week. Risk has dropped over the last few days, but the drop was from unusually high levels. Both MaryBlyt and CougarBlight say that infection risk is still high on those trees that still have open flowers, and the risk will increase somewhat over the weekend. If you add in a shower or two, then there is definitely a high risk of infection over the next few days.

The Hudson Valley and southern parts of New England may no longer have open flowers, but we have yet to see petal fall at UMass Cold Spring Orchard. In cooler parts of the MA and in other parts of northern New England, bloom is happening now. Even as Macs reach petal fall, it’s important to monitor all trees for open bloom, and keep an eye on fire blight risk until the flowers are gone.

If it does rain over the next few days, then it will be a major apple scab infection period, requiring fungicide protection or post-infection treatment. Again, be careful about using Regulaid or other spray adjuvants that increase chemical uptake with captan. It’s better to stay away from captan for a week or two to avoid phytotoxicity. Add mancozeb as a broad-spectrum protectant instead. If you’ve already applied streptomycin and need another streptomycin application on open flowers in the next few days, consider leaving Regulaid out of the mix and applying strep alone at the 24 oz/A rate to decrease risk of russet or other phytoxicity.”

We’ll discuss petal fall management needs later this weekend.