University of Vermont

By Terence Bradshaw

First things first: I’m going off-line later today for a rare, two-week, no-work vacation. Please note that I won’t be responding to emails that come in during that time.

Veraison is on or near in Vermont vineyards, which signals the start of the ripening period. That means a few things:

1. Get your pest management in order. Diseases should be kept down to a dull roar by now, and grape berry moth or Japanese beetle treated. Your window to apply fungicides that may affect fermentation, especially captan or sulfur compounds, is closing. It’s been dry, so there shouldn’t be too much in the way of late-season diseases if you managed them well so far.

2. Finish your canopy management. Grapes need to see the sun from now through harvest, so make your final passes through to comb shoots and pull leaves where necessary.

3. Get rid of green fruit. At veraison, you can see where certain clusters from secondary buds r less vigorous shoots are behind the others. Drop those now, they will only drag down the ripeness of the others.

4. Get your nets, squawkers, scarecrows, and other bird measures ready, but wait as late as possible.

5. Collect petioles and send in for analysis to assess vine nutrient status. See this post for more details.

6. A couple of weeks before expected harvest, start assessing grapes for ripeness. Sampling should be methodical and regular (at least weekly, or more often as harvest approaches). Generally a 100 berry sample is sufficient to ascertain general ripeness.

Sugar level and pH are easily evaluated with simple tools (a refractometer and pH meter, respectively) available from most winemaking supply outlets. We recently published a fact sheet on Preharvest Winegrape Juice Testing.
Remember that for most popular cold climate grapes, TA is a primary determinant for ripeness; for reds (Frontenac, Marquette), a target TA of 1.5% or lower is preferred; for whites, 1.2% should be considered the upper end, although La Crescent may frequently have higher values. Ideally, all grapes for winemaking should have TA below 1%, but that is not always possible for the cultivars that we grow. Work with any wineries you plan to sell grapes to to determine their preferred juice chemistry levels before harvest.

Enjoy the end of summer, and good luck as you plan for what looks to be a great vintage.

Best,

Terry

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

Always read the label before using any pesticide.

The label is the legal document for the product use.

Disregard any information in this message if it is in conflict with the

label.

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.

By Terence Bradshaw

We will host a veraison / preharvest vineyard management workshop at the UVM Horticulture Research & Education Center on August 6th, 3:00 – 4:30. This is folded into a larger Research Open House, I sent a flyer in a previous email (also available at: http://go.uvm.edu/hrecresearchday). We will cover out latest research on cold-climate grape cultivars, management decisions to be made as veraison approaches, and preharvest juice sampling to time harvest. There is no charge for this event, just show up. The rain date will be August 9, watch this email list for word if we do move it.

Most spraying in Vermont vineyards should be wrapping up as the vines and especially fruit are becoming resistant to most diseases. However, if you have downy and powdery mildew in the vineyard, it would be wise to maintain protection against them through veraison. Vines which have not reached bunch closure may also be protected against botrytis for one last time before veraison and harvest.

Japanese beetles are probably in every vineyard in the state. Their damage can generally be tolerated on established vines, but vines under 3-4 years old should be protected. Grape berry moth are mostly in pupal stages in Champlain Valley vineyards, although in some inland/cooler areas larvae may still be feeding. Careful and thorough scouting for webbing between berries will determine the presence of the pest. The threshold for treatment against the current generation is 6% of clusters with signs of damage.

Canopy management is critical at this time of the year- every fruit cluster should see at least some direct sun. However, if opening up congested vines at this time, be careful not to fully expose clusters that have been heavily shaded, as the risk for sunburn increases when a shaded cluster is exposed to full sunlight in midsummer.

Get your bird netting ready.

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

Always read the label before using any pesticide.

The label is the legal document for the product use.

Disregard any information in this message if it is in conflict with the

label.

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.

By Terence Bradshaw

High Summer is here, and this period from after July 4 through early August is the perfect time to apply some canopy management to the vineyard. By thinning and positioning shoots; removing unwanted clusters; and cleaning up trunks, we can significantly increase penetration of sunlight into the canopy and especially into the fruiting zone. This will make for measurably better juice and wine quality, improved winter hardiness, and less disease pressure.

There are a number of practices that should be performed, but the most important is shoot positioning (also known as “combing”). This practice includes separating each shoot from its neighbor and directing the growth into the vertical plane: usually down, for high-wire cordon vines, or up for those on a low wire, vertical shoot positioning system. Once shoots are pointed in the right direction, it’s easy to see where runty secondary or tertiary shoots are in the canopy, and where smaller clusters that are behind in development compared to the main crop are- those can both be removed.

(Retired) Iowa State Extension Specialist Mike White presents a good overview of the concepts and practices behind canopy management in his February 8, 2012 newsletter found here.

There’s a video of some UVM staff doing some (silent) canopy management here.

Ohio State Extension has a nice video here.

While I have you, it’s worth mentioning that we’re not out of the woods as far as disease management is concerned. It has been a difficult year so far with all of the rain, and the frequency of it, to maintain fungicide coverage but I have been seeing mostly clean fruit and foliage in vineyards which have maintained an appropriate spray schedule of 4-5 well-selected and –timed fungicides since prebloom. At this point, phomopsis is pretty much done, and black rot will soon be winding down. Powdery and downy mildews (PM?DM) should be the main focus for disease management, as well as botrytis a few weeks down the road. If this wet weather continues, I would recommend a specific botrytis material such as Flint, Rovral, Vangard, Endura, or Pristine before bunch closure (the point where berries size up to the point where spray material cannot penetrate the cluster to protect fruit from infection). As always, check your Pest Management guide (New York & Pennsylvania or New England guides) and the label, rotate fungicide classes to reduce resistance likelihood, and follow all safety precautions when spraying. Organic disease management spray options include copper (DM, a little PM), sulfur (PM), stylet oil (PM, do not spray before or after a sulfur spray), and possibly some of the biologicals but I don’t know enough about them in regards to their performance against these late-season diseases.

Next week would be a good time to scout clusters for grape berry moth (GBM) webbing which could suggest a need to treat for that insect pest. The threshold for treating this generation is 6% of clusters showing damage, which appears as small bits of webbing in between berries up inside the cluster. GBM is the primary insect pest of established vineyards in Vermont, and if it is the only pest insect need to manage, then some very specific materials with low potential for non-target effects may be used, including lepidopteran-specific materials like Bt, Intrepid, Delegate, or Altacor (the latter has some activity against Japanese beetle). Bt (DiPel and others) and Entrust would be effective materials against GBM for organic growers- the former affects only lepidoptera, while the latter would have some activity against Japanese beetle and some other insects as well.

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

Always read the label before using any pesticide.

The label is the legal document for the product use.

Disregard any information in this message if it is in conflict with the

label.

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.

By Terence Bradshaw

Many vineyards are in bloom across Vermont, and inflorescence looks good and bodes well for a promising year. As I’ve been saying all along, be sure to maintain spray coverage for the next couple of weeks; to remove any diseased tissue as you find it; and to do your best to maintain an open canopy (more on that in a minute). All of the main diseases, including downy mildew, should be active now, so fungicide choice should cover all of the bases. That likely means applying a mix of materials that have multiple modes of action, like mancozeb (watch the 66-day preharvest interval) or captan and a strobilurin (Flint, Abound) or DMI (Rally, Elite, etc.). There are some good premix materials available that cover two modes of action, like Inspire Super and Pristine, but even they could use some protectant activity from mancozeb or captan to improve efficacy and reduce resistance development. The New England Small Fruit Management Guide has a good table that outlines the efficacy of the main fungicide materials available to growers. For organic growers, a rotation of sulfur and copper is pretty common now, but be sure to watch for signs of phytotoxicity. Coverage maintained for the next few weeks will pay off by allowing you to relax a bit for the second half of the summer.

Wild grape bloom occurred on June 19 in South Burlington, which sets the clock for grape berry moth management. The first overwintering generation is rarely significant enough to warrant a management spray except in vineyards that have had extreme damage in previous years. Each generation requires about 820 degree days (base 47°F, or DDb47°F) to complete, and the first generation typically emerges around the time of wild grape bloom. So if we use June 9 as our ‘biofix’ and track DDb47°F, we can estimate the best time to treat for the more damaging later generations.

This is made easy by the Network for Environment and Weather Applications (NEWA) system, which I coordinate for Vermont. The network includes twelve on-site weather stations (all located at orchards) and six airports, and imports data in near real-time for use in pest models. It is free to use, and growers can locate the site nearest them and develop a best-guess of phomopsis, black rot, and downy mildew infection periods as well as a sense of the grape berry moth generational development.

Plant tissue sampling is one of the best ways to plan fertility management in your vineyard, and now is one of the important times for collecting samples. Petiole samples may be collected at bloom or veraison, and comparisons between years or blocks should be based on the same time of collection. The benefit of a bloom sampling is that it gives you time to make corrections, if needed, during the present growing season.

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 closest analytical lab for grape petiole analysis that also provides pretty comprehensive management recommendations is the . There is a great section in Appendix A of the Wine Grape Production Guide for Eastern North America (which every grower should have a copy of on the bookshelf, ready to grab with short reach) which helps to guide fertilizer application rates based on soil and petiole samples. If you have a copy of those to send to me, I’d be happy to help you with the numbers as well.

Finally, I have two events to mention. First is a reminder of the July 9 Canopy Management Workshop we will hold at Ellison Estate Vineyard in Grand Isle. Please preregister here to attend.

The second is a UVM Horticulture Research & Education Center Research Open House that we will hold at the farm in South Burlington on August 6. Researchers with projects across the farm and working in multiple disciplines will showcase our work. I will host a tour of the research vineyard, and will have a pre-harvest management workshop at which we will discuss bird protection, late-season canopy and crop management, and preharvest sampling procedures to optimized juice quality at harvest. Watch for details on that event in the next week or so, but plan on it happening in the later afternoon around 3:00.

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

Always read the label before using any pesticide.

The label is the legal document for the product use.

Disregard any information in this message if it is in conflict with the

label.

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.

By Terence Bradshaw

June 19, 2019

It’s always impressive to me how fast grapevines can go from zero to full foliage in a matter of a couple of weeks. Vines at the UVM Horticulture Research & Education Center are generally at 16-24” shoot growth. We’re not quite at “Immediate Pre-Bloom” stage, but not far off, either. Now is a critical time for disease management. As we mention in our initial IPM strategy for winegrapes, all of the major diseases save for late-season fruit rots are sensitive to management right now. That means that fungicide applications should be made, using a material or materials with broad range of coverage against powdery mildew (PM), downy mildew (DM), black rot (BR), anthracnose (Ant), and that last bit of phomopsis (Ph) for the season. Generally, this means a combination of materials, including a protectant (mancozeb, most effective against Ph, BR, PM, or captan (Ph, DM)) plus a systemic or more narrow-spectrum material. Those may include Vivando / Quintec (PM only); a DMI material like myclobutanil or tebuconazole ((BR, PM); or a strobilurin (BR, PM, also excellent against botrytis so save until later in the season in July if you have issues with that disease). I’ll mention other materials with excellent efficacy against DM and botrytis later when those diseases are of greater relative concern.

For organic growers, be sure to maintain your copper and/or sulfur sprays, watch for phytotoxicity, and remove diseased leaves and clusters as soon as you see them. It’s been a wet spring, although a bit drier since grape budbreak that earlier in the year. I expect diseases will be pretty significant problems for growers this year, so stay alert.

Insect activity is usually pretty quiet at this time of the season. Keep an eye out for bloom on wild grapes, as that sets the clock for the degree day model used to time management of grape berry moth (GBM). We typically add BT (Dipel, Javelin, etc.) or another material specifically active against lepidopteran pests soon after bloom at the earliest, so there’s time before we consider managing for this pest. GBM isn’t always a problem in every Vermont vineyard, we’ll talk about scouting for that pest in an upcoming bulletin.

We are seeing a bit of grape tumid gall (GTGM) in the UVM vineyard this year. This is an infrequent pest that causes visually striking but (usually) relatively insignificant damage to the vines, and management practices are not recommended against them. However, serious cases can affect fruit clusters, especially in La Crescent and Marquette, so any signs of them in clusters may warrant treatment. I discussed this pest in a post on June 8, 2017:

This insect is similar to phylloxera in that the larvae feeds on leaf tissue which responds by forming a protective gall around it. GTGM is different in that it also affects rachises and fruit, and when the galls become fully engorged, can look pretty dramatic.

Figure 1. Grape tumid gall on a fruit cluster in midsummer. UVM vineyard, 2009.

GTGM is an midge insect (small fly) that lays eggs on grapevines. Flies are ephemeral and only live a day or so; management should not be targeted at adults. Hatching larvae burrow into vine tissue and are thus protected from contact insecticides. In most vineyards, GTGM is considered a minor pest or even a curiosity as the galls can be quite drastic-looking. That said, I have been hearing reports of high levels of GTGM in vineyard this year, and some of these vineyards reported them last year under different management, so I suspect that certain vineyards have increasing and potentially problematic populations.

Figure 2. GTGM on Marquette, UVM vineyard, 2010..

Vineyards should be scouted before assuming you have a problem with this pest. There is no threshold established, as most growers tolerate low levels of damage. However, I have heard reports of 50% or more leaves affected in some vineyards, and I can’t imagine how that wouldn’t negatively affect vine productivity.

Figure 3. GTGM on inflorescence. UVM vineyard, 2011.

Sanitation is an important method of reducing GTGM populations and may be enough in low-pressure situations. Galls can be crushed if seen on leaves, or severely affected leaves removed and destroyed. In organic vineyards, as always, this should be the first line of defense since spray options are minimal. If the extent of damage is beyond physical removal, an application of Movento is the best (only) recommended option I can find. Movento is a systemic insecticide with a unique mode of action and is listed as posing low risk to wildlife, and as non-toxic to fish and birds. It is best used at first sign of galls, practically speaking, as scouting for hatching larvae (which hatch from microscopic eggs) is difficult under normal field conditions.

GTGM may be distinguished from phylloxera by the gall surface, which is smooth compared to phylloxera which is bumpy or warty. Movento is effective against phylloxera as well as GTGM and has a long residual control period, so may be a good material if either or both of those pests are common in your vineyard.

More information on GTGM may be found in this Cornell fact sheet: https://ecommons.cornell.edu/bitstream/handle/1813/43134/tumid-gallmaker-FS-NYSIPM.pdf?sequence=1&isAllowed=y

Horticulture: There are two good times to collect petiole samples to assess vine nutrient status, bloom and veraison. Generally, you should stick with whichever timing you have been using so that you may compare to past tests. Dr. Joe Fiola at University of Maryland has a good fact sheet on petiole sampling. We recommend the Cornell Nutrient Analysis Laboratory for petiole sampling, as they have extensive experience in providing nutrient recommendations for grapes. Should nutrient applications be needed, this is a good time to apply boron, magnesium, and nitrogen as they are needed during this period of rapid shoot and fruit growth.

Other activities that I don’t need to tell you about: shoot thinning can continue, but shoots aren’t lignified at the base enough to comb them, they’ll just break off. Keep the vineyard mowed to improve airflow, but a golf course mowing regime isn’t necessary unless that’s your aesthetic choice. Keep the in-row weeds down however you can, but most herbicides should be put away for now because of likelihood of vine damage.

Where trade names or commercial products are used for identification,

no discrimination is intended and no endorsement is implied.

Always read the label before using any pesticide.

The label is the legal document for the product use.

Disregard any information in this message if it is in conflict with the

label.

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.