This edition of our newsletter was written by UVM PhD student Bethany Pelletier. You can expect more from her this season. While I have you, I’d like to promote the Cold Climate Viticulture course Bethany and I will be teaching at UVM this summer. We haven’t finalized this year’s syllabus, but you can see the 2023 syllabus here. This course is only offered in alternate years, so will not be available again until 2027. Please reach out to me if you have any specific questions about it.-TB

Spring has sprung in Burlington Vermont! Here in South Burlington, some of our earliest varieties like Marquette and Foch are looking pretty close to bud burst. Here are some things we should all be thinking about around this exciting time of year;

Our first line of defense for ALL growers is going to be good pruning and sanitation techniques. We should all be just about pruned up by now, but it’s never a bad idea to do another vineyard walk and make sure you didn’t miss a vine or two. Taking the extra time to clear out any dead wood or at least flail mow to break it apart will make a HUGE difference in the presence of our early season fungal pathogens like black rot and Phomopsis. Be sure to discard this material far away from the vineyard, not just at the end of a row.

As buds reach 1-2” height it will be time to shoot thin. We want to take it down to 3-6 shoots per foot of canopy, ideally keeping the primary shoots where possible. Many of our cold climate varieties like to push out their secondary shoots alongside the primaries (as pictured below, the primary is the larger shoot coming out at an angle). We should try to favor the primary shoots as they will have more flowers and generally develop into a stronger cane. This is also the best time to flick off any buds coming up on the trunk that we don’t want for future replacements, as these can REALLY gum up the airflow of the canopy. Shoot thinning is another IPM tactic that will make a huge difference in your disease defense regardless of your pesticide strategy. A cramped and crowded canopy will make a dark and humid microclimate, encouraging more mildews later in the season. In addition, more shoots will mean far more labor for you down the road when it comes time to shoot thin; much more pleasant to knock some shoots down while they’re still young and small!

UW Fruit Program

While proper pruning, sanitation, and shoot thinning will always be your first line of defense in the vineyard, we should all still be thinking about our pesticide management plan for the season. Pesticide orders should be placed by now, and spray equipment cleaned and calibrated. For all growers, but in particular those that use live biopesticides, be sure to check expiration and efficacy dates on your materials. Biopesticides and many organic pesticides often should be replaced yearly for maximum efficacy.

For the first time in my years as a student at UVM I am seeing some notable numbers of flea beetles. I’ll attach a picture here, they may look familiar to you already!

Tom Zabadal. MSU College of Agriculture

I am not too concerned about these at the moment, given that bud swell is progressing fairly rapidly so these little guys will only have a few more days to get any bites in. But if for whatever reason our bud development stalls out, we may want to consider some sort of control. If this happens to any of y’all please poke our fruit team for some management options.

Now that pruning is over and the vineyard is looking nice and neat, it can be easy to forget just how essential these early weeks are for disease prevention. Cold climate cultivars are typically not in need of pesticide intervention until about 5-8” of growth. However, if you are an organic grower or had bad early season disease last year you may want to start putting down some protection sooner! In the UVM vineyard we have both conventional areas and ‘organic’, so I am already planning my future sprays. Here are some tried and true suggestions from our own Dr. Bradshaw;

“The primary disease of concern at this point is phomopsis, as rachis infection at this point in the season may cause significant fruit loss at harvest. Anthracnose may also be active at this point , given the warm/hot weather are expecting later this week. Vineyards that have had recent problems with those diseases or organic growers using copper or other less-effective materials may consider treating this week; if you haven’t had major problems with those diseases, treatment can wait until the 5-8” growth stage as long as you are using a highly effective contact fungicide like mancozeb or captan. Organic growers are in for a bit more work. The standard fungicides, copper and sulfur, have only fair efficacy against this disease at best.

It is worth noting that both copper and sulfur (including lime sulfur) can cause phytotoxicity on certain cultivars. Dr. Patty McManus summarized her research on copper and sulfur sensitivity in cold-hardy grapes in the 2/8/16 Northern Grapes newsletter, and I’ll summarize it to say that Brianna should receive no copper; and Frontenac (all types), La Crescent, Leon Millot, Marechal Foch, Marquette, and St. Croix should receive no more than 2-3 copper sprays per season. Save those for later when black rot and downy mildew become bigger concerns. Sulfur sensitivity was observed on several cultivars, and its use (including lime sulfur) is discouraged on Foch, Millot, Brianna, and Louise Swenson; with limited (2-3) applications suggested on LaCrescent and St. Croix.” -T. Bradshaw, 2024

I believe that’s all for now folks! I wish you all the best of luck this growing season, and fingers crossed that this lovely warm weather stays with us through bud break! I’ll be back again soon with disease outlooks and funny stories from our own vineyard.

Best,
Bethany Pelletier & UVM Fruit Lab

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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