May 15, 2014

By now most orchards in the Champlain Valley should be at full pink, and a few blossoms were observed open today at the UVM Hort Research and Education Center in South Burlington. This is a critical time for management activities in the orchard, so here goes:

1. We are still in a high fire blight risk situation for nearly all orchards in the state. Hot weather the past few days has pushed epiphytric infection potential for the fire blight bacteria to levels sufficient to cause infection. If you or an immediate neighbor have had fire blight in the past two years, you should be ready to treat opening blossoms within 24 hours. We are going to get the required wetting for infection starting on Friday, and blossoms must be covered with streptomycin within 24 hours of infection.
2. For a more long-term, systems-based management program for fire blight, please see the guide, “Grower Lessons and Emerging Research for Developing an Integrated Non-Antibiotic Fire Blight Control Program in Organic Fruit,” available here. Frankly, if you are not bound by organic certification rules (and even for this final season organically-certified growers are allowed to use it), streptomycin is your best defense against blossom blight and will help limit shoot blight spread later in the season. This guide however offers many good strategies for use in a long-term program that taken together will reduce your orchard’s susceptibility to the disease.
3. Bloom looks variable; I have one of my lighter crops at the UVM orchards, but I saw a very good density of fruit buds in Grand Isle County today. Anecdotal reports from Addison County indicate either a great fruit bud density or a moderate one. I would appreciate any feedback on bloom conditions in your orchard.
4. Scab is still a significant risk, and this weekend’s rain will likely initiate a significant infection period. This is a good time to add one of the systemic SI, QOI, or SDHI fungicides to your spray schedule to cover for powdery mildew and cedar apple rust as well as scab. There is some concern with application of Captan and potential phytotoxicity around and just following bloom, so a combination of one of the ‘big gun’ fungicides and 3 lbs/acre mancozeb would be a reasonable tank mix at this time. If you haven’t used more than 3 lbs/acre of mancozeb (or another EBDC ) in any tank mix yet this season, you can continue to use it after bloom until 77 days before harvest at that rate.
5. Speaking of scab, lesions from the first infection periods of the season, especially from around May 1, should be visible by early next week.
6. If you haven’t applied ground fertilizers yet, now is the time to do so. Same for irrigation, new high-density plantings are thirsty, so be sure to water regularly. NEWA has a good Apple Irrigation model under the ‘Crop Management’ tab.

That’s all for now. Stay dry, but keep your orchards covered.

Terence Bradshaw, UVM Tree Fruit and Viticulture Specialist

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The UVM Tree Fruit and Viticulture Program is supported by the University of Vermont Agriculture Experiment Station, a USDA NIFA E-IPM Grant, and USDA Risk Management Agency Funds.