Veraison in Vermont vineyards: birds, petiole testing, disease, harvest planning

Grapes are at or near veraison in Vermont vineyards, which signals the start of fruit ripening. At the UVM vineyard, have observed Marquette at veraison as of at least August 4, Petite Pearl and Itasca are changing color about now, and Verona is just around the corner.

This is an important time of year for a few activities. First, bird damage can be expected to begin and increase as fruit ripen. Birds will harvest your berries just a day or two before you’re ready to, so if you don’t have damage yet, don’t think you’re out of the woods. Netting is the best method of protection. Auditory scare calls, propane cannons, and inflatable ‘used car lot’ balloons are sometimes used as well, but their effectiveness is questionable and their annoyance factor significant. Dr. Alan Eaton from the University of New Hampshire wrote a good guide on prevention of bird damage in fruit plantings, available at:

Now is the time for plant tissue testing as well. Petiole samples may be collected at bloom or veraison, and comparisons between years or blocks should be based on the same time of collection. Samples should be collected separately for each cultivar or block. In each sample, a random collection of 75-100 petioles should be collected from throughout the planting. Petioles should be collected from the most recent fully expanded leaf on the shoot, not across from the fruit cluster as is collected for a bloom sample. Just remove the whole leaf and snip the petiole (the leaf ‘stem’ off with your pruners. Gently wash each sample in water with a drop of dish detergent, then rinse fully and place in an open-top paper bag to dry. The best analytical lab for grape petiole analysis that will provide recommendation for next year’s nutrient inputs is Dairy One, which is associated with the Cornell Nutrient Analysis Laboratory . Video about petiole sampling:

Disease management: as fruit ripen, they will become more susceptible to the various bunch rots, including botrytis, ripe rot, and sour rot, and canopies can be affected by late-season downy and powdery mildew. Good cultural management for all of these includes keeping the canopy open, ensuring that clusters can ‘see the sun’ by shoot combing / thinning, removal of leaves, and pruning of laterals. There may be a few sprays warranted at this time, with some big caveats. Copper, sulfur, and captan should be avoided as we approach harvest, as they can either inhibit fermentation of contribute to off-flavors in the finished wine. Consider preharvest intervals, too. Visible downy mildew can be managed through leaf removal, or application of one of the various Phosphorous acid products (e.g., Rampart, Fosphite). Some other materials that have efficacy against DM may be found in the New England Small Fruit guide. Be sure to rotate fungicide resistance classes (FRAC codes). There may be a bit of powdery mildew in the vineyard as well, that can typically be managed with a thorough application of stylet oil, applied as soon as it is observed in the vineyard. Botrytis can be specifically managed with fungicides, but it will be difficult to get into any closed clusters like Petite Pearl, and that disease is best managed during the immediate postbloom window. Remember that not all varieties are equally susceptible to disease, and loose-clustered varieties tend to have less issues with botrytis overall. There is some concern regarding spotted wing drosophila (SWD) and its potential to damage ripening fruit, which leads to sour rot infections. This invasive pest has been seen in high numbers in the region this year, but that does not suggest cause for alarm among the vineyard community. SWD have lower preference for grapes than for other soft fruit, and winegrapes that will be processed immediately after harvest are less prone to damage from secondary diseases. Still. Good vineyard sanitation is key in managing this pest. Any damaged clusters with cracked fruit should be removed from the vineyard in the weeks between veraison and ripening, as these attract SWD and other rot-bearing fruit flies. SWD have a preference for protected, shady areas in the canopy, so, again, keeping clusters exposed to sun is a helpful practice. While there are many insecticides labeled for control of SWD, I do not recommend their use in vineyards in any but the most specific cases.

Start making plans for harvest and crush now. This may be a good time to thin out any lagging ‘green’ clusters that developed from secondary buds and are lagging in ripeness. Remember, you’re looking for crop uniformity. You can estimate yield by counting clusters on a few representative vines and multiplying by the typical cluster weight for your vineyard. If this is unknown, use 0.25 pounds (113 grams) per cluster, which is the average we have recorded at the UVM vineyard for Minnesota cultivars from 2010-2015. Your formula should look like this:

Estimated tons/acre = average # clusters/vine * 0.25 lbs/cluster * # vines per acre /2000 (pounds per ton)

For the UVM vineyard, where we have 726 vines per acre [43560 sq feet/acre / (6 feet between vines * 10 feet between rows)] = 726, the crop estimate for 50 clusters per vine is:

4 tons/acre = 50 * 0.25 * 726 / 2000

Three to four tons per acre is a good crop for mature, healthy vines for most cold climate cultivars; some vigorous vines in good health may support higher crop yield but I wouldn’t push mush more than 5.5 tons per acre lest you compromise ripening. If you have too many clusters, thin out the smallest and greenest ones to get your target cluster number. This exercise will help you plan lugs, bins, and tank space, as well as allow you to communicate that information to any wineries you plan to sell to.

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Late summer, and harvest date window for apples

In the time since I last reached out, some orchards have been deluged with rain, others haver received welcome and needed moisture. As we approach harvest (I picked my first, just under-ripe Williams Pride apple today), it’s important to get our ducks in a row.

Spraying should be wrapping up soon. I hope growers have been using red sticky traps for apple maggot fly management. I have seen myself and heard others’ reports that AMF are on the low side this year. Don’t take my word for it- pay attention in your own orchard, as damage will only get worse as fruit start to ripen. It’s also a bit on the late side but still in the window to treat for second generation codling moth where you have that problem (again, your traps will tell you). I plan to treat our orchard on Monday with Assail to manage both of those pests.

Summer diseases may be more of an issue this year, especially where maintaining fungicide coverage has been difficult with all the rain. One last treatment with a DMI or strobilurin product should get you to harvest, especially if mixed with a little captan. Fire blight is still around, too. We are still seeing it in the UVM orchard, which I attribute to cutting it out during rainy July. Advancement does seem to be slowing, but a cut thorough cut-out before harvest will help to reduce the inoculum load in the trees next year.

Keep applying calcium, especially on Honeycrisp, Cortland, Northern Spy, and other large-fruited varieties.

There have been some questions about early maturity this season. I ran the Cornell Harvest Maturity Model for McIntosh using HREC data from South Burlington, and came up with a recommended last harvest date for CA storage McIntosh of September 11. This is indeed about a week early. The model is largely driven by heat units in the 30 days after bloom, as well as the actual bloom date. This spring was generally (but not always) warm, and bloom a bit early. However, take this model with a grain of salt. The nature of the model- predicting date for CA storage of McIntosh- dates back to a time when we were predominantly a a) McIntosh industry and b) wholesale / packing house industry. This means no disparagement to those who still operate on a wholesale production and sales model, but those of you who do should use more accurate starch index testing (details in the same link) to time harvest. Starch iodine solution is available here. Another important caveat is that this model, published in 1992, is based on a climate and growing conditions that we can no longer count on e.g., cool nights in September; moderate summer high temperatures; and larger, somewhat shaded semidwarf trees. So take that all with a grain of salt, but I’ll agree- from my observations, we’re running about a week early. I expect this will moderate as we approach fall, though.

Finally, we all ought to be prepared for another round of COVID affecting or operations. Things are moving fast- UVM just instituted a mask mandate for indoor spaces yesterday, and new restrictions may be coming down the pike. This isn’t our first round with this, and arguably many orchard did better as customers flocked to outdoor activities last fall. Let’s all be wary of new developments and use a little extra caution and common sense. I’ll pass on any further guidance I get from the state as it comes.

Take care,


Survey: Grape Growers in New England and New York

Here’s a gentle nudge, we’re hoping to get the best response possible from the industry. I know things are busy, but stakeholder data from surveys like this is exactly what we need to help develop programs to support our grape and wine industry. Please consider spending a few minutes to add your data to the set. It will take less time than it does to drink a glass of wine. -Terry
If you are a commercial grape grower in New England or New York, please fill in the survey below so we know how to better help you.

Your response will be used to prioritize future Extension and research efforts.

It should take between 5-15 min. The deadline is Friday August 6, 2021.

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Elsa Petit, Sonia Schloemann, Jessica Ellis and Max Resnick on behalf of the UMass Extension Fruit Program