Vermont orchards are generally at green tip bud stage for the coolest locations in the state to tight cluster in warmer locations. Apple scab continues to be the primary pest management consideration of concern. I recommend maintaining a protectant fungicide and, given the off and on wetting of the last few days that has likely resulted in an extended infection period for most orchards, a single site fungicide with kickback activity such as those in FRCAC codes 3, 7, 9, or 11 (remember to rotate these chemistries to avoid development of fungicide resistance). Weather for spraying conditions has been all over the place this week with high winds on many days. It seems the best time for extended low wind conditions appears to be Wednesday night through Thursday morning. We are expecting, fairly substantial rainfall on Friday, which should result in the next major infection period.

As we approach bloom, it is important to consider the potential for the development of fire blight. I recommend having one application of streptomycin on hand as we head inro the bloom period. Streptomycin is always best used in conjunction with a degree day based fire blight model. Strep is extremely effective against blossom light infections when applied within 24 hours of infection and where bacteria has not developed resistance to it (and I have not yet seen evidence of strep resistant bacteria in Vermont.) There are other measures that may be taken to reduce reliance on streptomycin or increase its efficacy. Some biological control materials, (e.g., Lifegard, Actigard, Regalia) are labeled as an act as systemic acquired resistance promoters. These materials act like a sort of vaccine that prompts the tree’s immune system to fight off fungal and bacterial infections after application. While the data do not show complete efficacy against devastating diseases like fire blight, recent work (1, 2) done in New York State by Kerik Cox and Anna Wallis shows that they have potential to control blossom and shoot light at levels between a non-treated control and a streptomycin application. Where you may have had fire blight problems in the past, the use of one of these materials prior to bloom (as in this week) may help to reduce disease incident if infection occurs. Unless you are under constraints as an organic grower, I still recommend using streptomycin if the models call for it in your orchard. However, for growers, who have faced substantial fireplace problems in the past, the use of these materials may be affective in helping to get the disease under control in this in future season. The evidence is also good for the efficacy of low-rate(3 oz/acre) prohexadione-calcium (e.g., Apogee, Kudos) applied at pink bud stage followed by four biweekly applications at 2 oz/acre in reducing shoot blight symptoms.

Now is the time to get pheromone baited traps up for monitoring lepidopteran (moth) pests. The one that we monitor for most closely and which most likely drives management decisions is codling moth. Pheromone baited traps should be hung one per acre block and should be located 50 feet or more from each other to reduce the attractive effects from one trap to another. Pheromone capsules are specific to the type of moth that you were trying to catch, so each trap should include only one capsule for only one particular moth. For codling moth, we hang traps prior to bloom and check them daily, especially during warm weather, and record the date of first moth capture. I posted a video to our YouTube channel of me assembling and hanging a CM trap yesterday. That date can be used in the NEWA degree day model to time spray application toward freshly laid eggs or hatching larva. It is this precision of timing and maximizing efficiency of pest control materials that allows growers to use relatively expensive, highly selective (not harmful to most beneficial insects), and worker safe materials in a cost-effective manner. This year at the UVM orchard we are using pheromone traps for codling moth, obliquebanded leafroller, dogwood borer, and oriental fruit moth.

Growers should also be checking European apple sawfly traps that were hung last week and making counts of trapped insects. In some years, EAS may require treatment prior to bloom. We try to avoid the use of any insecticides at this point in the year because wild pollinator populations are increasing and we want to reduce the likelihood of residues that wild and managed honeybee pollinators are exposed to when visiting flowers during bloom. High levels of sawfly could cause substantial fruit damage, especially when bloom, when we are prohibited from using any insecticides, is extended. In the unlikely event that a pre-Bloom insecticide is used, I recommend, a relatively short-lived material such as a pyrethroid, and do not at all recommend the use of neonicotinoid material which have a high likelihood of having toxic residues in pollen and nectar that are collected by pollinators during bloom.

It’s time to really think about getting your nitrogen and other fertilizers on as the trees will be rapidly developing tissues in the coming weeks. If you are using granular fertilizers, I recommend split applications and applying half pre-bloom and the other half in early to mid-June, being sure to complete all nitrogen applications before the end of June to reduce likelihood of winter injury in the following season. If you have not yet it is a good idea to apply boron and zinc foliar fertilizers to strengthen developing blossoms prior to bloom.

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

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