As we wrap up what could be a substantially damaging week for Vermont Apple Growers, I am heartened to have heard very little about damage from Monday night’s frost event. (Please report any damage in your orchard here). That doesn’t mean that there isn’t damage out there— we have heard reports of substantial damage just to the south of us where buds were a couple bud stages more advanced than in many Vermont orchards. At the UVM Horticulture Research and Education Center orchards, I assessed some buds on McIntosh, which was at green tip, and Zestar, which was more advanced at the early tight cluster bud stage. Our weather station recorded a low of 24° that night, and I expect that in some areas of the Orchard, especially near the ground, we had temperatures as low as possibly 22°. No Macintosh buds showed damage, however, about 10% of Zestar buds had damage on the king bloom in the cluster. All lateral blossom tissues were intact. This suggests that, at least at our orchard, the damage was minimal and can be managed through normal crop management and thinning procedures. It is best to assess your own orchard carefully before we get into thinning season.

I had a good IPM moment last Saturday when I went into the farm to give a lesson to an undergraduate pesticide applicator training course on sprayer operation and calibration. Since I was going in for a morning class anyway, I had planned to put on our green tip fungicide as I had recalled that there was to be rain in the forecast. When I got to the farm around 4 AM I was preparing my spray records and double checked NEWA. Following the scab model, I saw no risk for apple scab infection in the next 3 to 5 days, so I put the sprayer away and took a nap before class. I have been following NEWA every day, as we all should be at this time of year, and still have not seen substantial risk for apple scalp infection, so we have not sprayed the orchard since our copper spray on April 13. This does potentially leave the orchard in a vulnerable situation if a substantial scab event occurs, as we do not have any fungicide material built up on the trees so we will need to be ready to apply fungicide when the next infection period appears to be upon us, as we are approaching the advanced phase of ascospore maturity.

That doesn’t mean that it’s not still spraying season. This is the time to get in row weeds under control, so herbicide applications would be prudent. This is also an excellent time to apply oil to trees that are no further along than tight cluster bud stage. Oil should be applied at a 2.5% rate to trees that are at silver tip, 2% if trees are no further than green tip or early half inch green, and you could apply at a 1% rate to trees that are at the tight cluster bud stage. I would not apply oil to trees that are past the tight cluster blood stage, for fear of phytotoxicity. When applying oil, the percent rate is just that – 2% oil means 2 gallons of horticultural spray oil in 100 gallons of water. Water should be applied at a dilute rate so as to thoroughly wet the trees, this typically means around 100 gallons per acre. This is also a good time to apply pre-bloom foliar nutrients, such as zinc, nitrogen, and boron.

We will soon be setting insect monitoring traps in the orchards (pdf monitoring guide). The first traps that are set are for tarnished plant bug, and those could be set anytime now (video here). However, tarnished plant bug is not a substantial pest for most retail facing orchards. The damage from TPB is solely cosmetic, and it rarely reaches the level that affects perishable or marketable yield for pick your own or farm market-oriented orchard. The next traps that will be set are the same white sticky card traps used for TPB, these are set for European apple sawfly at the early pink bud stage. Traps should be placed at head height, at least three per orchard block, and monitored through bloom. EAS is both cosmetic and can be a substantial yield-reducing pest if in high enough population. I still typically do not recommend pre-bloom insecticide for most orchards, but orchards that have a history of European apple sawfly or in years where bloom is protracted, which prevents the application of a petal fall spray for several weeks, may call for treatment before 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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