By Terence Bradshaw

I had an email come in tonight that I imagine includes a question on many people’s minds. That is, as we near veraision (I saw my first Marquette changing color today), what do we need to worry about as far as spotted wing drosophila (SWD) is concerned? SWD (Drosophila suzukii) is an invasive species of fruit fly with the unique ability to lay legs in intact (i.e., undamaged) fruit, thanks to its serrated ovipositor. Mated female adults use that tool to lay eggs into developing fruit. The ovipositor puncture is a great site for rots to move in; the eggs in the fruit hatch into maggots that eat out the insides of fruit and lend to more rot. This isn’t a fun pest, read more about it at: http://fruit.cornell.edu/spottedwing/.

In general, cultural measures are the first and best line of defense against SWD. There are many practices that can reduce SWD populations and reduce susceptibility in grapes. One really nice thing is that the practices that make for high-quality (ripe) grapes also help to reduce SWD infestation.

The best thing is that grapes are not a ‘top’ preferred host for SWD- they’ll go for many other crops first. Generally, they come in after working over other more desirable crops, including wild choke cherry, elderberries, and similar soft fruit. Of course, raspberries and blueberries are the most preferred cultivated crops, and netting is becoming a more common practice used on those crops. Less so on grapes- the tight weave needed to keep out SWD would reduce the critical sunlight that is needed to fully ripen winegrapes, and as you get to larger acreages, the cost becomes prohibitive. Where a grower is not limited by organic certification, there are more tools available to manage SWD and other pests, but pesticides should not be the first defense against this pest. You’ll be playing a losing game and find yourself doubling down with increasing regularity

The scent of fermenting/rotting fruit will bring SWD into the vineyard more quickly, so do everything to maintain fruit quality and to prevent damage. That includes managing for disease, maintaining an open canopy, shoot thinning / positioning, cluster thinning, leaf removal, you know the drill. The higher quality (and the more defect-free) the crop, the less likely they will be to draw in SWD.

Sanitation should be a first line of defense against SWD. Any fruit that are decaying need to go, not on the vineyard floor, but buried into a compost pile. If you do feel a need to treat (spray) for them, I would recommend doing so as a secondary pest when spraying for grape berry moth (GBM). That is, treat for GBM (more on that shortly), but instead of using a lepidopteran-specific material like Intrepid or Bt, use something with activity against diptera as well. Delegate (spinetoram) is the preferred material, Entrust if you’re certified organic. Do Not get into the game of spraying either of these materials on a 7-10 day basis until harvest, it’s a losing game. Not only will you likely build up resistance in the SWD population to your pesticide of choice, but you’ll kill any potential predators that may fee on SWD in the vineyard. One, maybe two shots are plenty, and remember to time them against grape berry moth. Notice I’m not suggesting using pyrethroids (e.g., Danitol) or carbamates (e.g., Sevin) against these insects, as they are generally too harsh on predator insects.

GBM are starting to show up in Vermont vineyards- some sharp-eyed students of mine scouted our vineyard and found that we were over threshold and need to treat for that insect. We’re also running up against the bunch closure window after which it gets much more difficult to manage GBM (or SWD, for that matter) that are tucked up in the cluster happy. Protected, and fat on your ripening and rotting grapes.

So this is it- time to get out there and optimize the conditions for what looks like another fabulous vintage. Manage that canopy, expose those clusters, treat these couple if insects, and get your netting ready. Harvest will soon be upon us.

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

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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

Sorry grape growers, you just received my comments on orchard activities for the immediate time being. The good thing, as my predecessor Dr. Lorraine Berkett used to say when discussion apples and grapes, is that it’s the same story with different characters. So, here we go with Act One:

Weather has been as dry in vineyards as it has in orchards, although some sites got a good soaker on Monday. We are expecting rain next week, and the fruit clusters are at ‘berry touch’ stage and we’ll soon see bunch closure when it will be more difficult to get protective materials into clusters. The main diseases of concern are spot outbreaks of powdery mildew, downy mildew, and possibly botrytis as we approach veraison/harvest. The good thing is that primary infection of all of these were low, so there’s little secondary inoculum out there to cause problems. However, good IPM suggests not only reducing pesticide applications unless the biology says they are absolutely necessary, but also targeting critical management points so that diseases may be managed “one and done” and not have to fight them longer through the season. I’ll summarize that point later.

Our main insect of concern is grape berry moth (GBM), which is also difficult to manage after bunch closure. The threshold for this pest is evidence of webbing between berries on 6% of inspected clusters, but I would be a little more conservative if that window is due to close. Bt is an effective and low-impact material for use against GBM, as are Delegate, Altacor, and other lepidopteran-oriented materials.

Japanese beetles are a concern for young vines, they can be managed with numerous materials including carbaryl, Assail, and Avaunt; or Surround and Pyganic for organic growers. Note that those are more broad-spectrum materials than the ones I suggested for GBM, and I generally steer clear of them unless necessary. Really, most vineyards can tolerate any Japanese beetles that they get.

Spraying summary- I’d lean toward applying something in the next 7-10 days against GBM if you’re seeing damage, and consider a downy mildew fungicide at the same time. That might be it for the season unless things get wet and we’re seeing the mildews (downy and powdery) showing up on foliage.

Canopy management: this should be priority #1 now, get those shoots combed first, but don’t really worry about leaf removal given the high amount of sunlight we’ve been getting. This is also a time to think about final crop load, I’ve received a question or two about estimating the crop to plan harvest or to help with dropping excess crop. The concept here is that you can fairly easily guesstimate the potential crop by knowing three variables: average number of clusters per vine, average cluster weight at harvest, and actual vines per acre. This is when past records are helpful for determining average cluster weight at your vineyard. If you don’t have them, I’ve used numbers from Cochran and Smiley’s Review of Cold Climate Grape Cultivars in the past, but I’ve also way overestimated doing that. Another estimate that is used is the lag phase method, which assumes that grape clusters are about half their final weight during the midsummer window when berry growth slows. Despite its use by Oregon Pinot Noir growers, the timing of the lag phase is difficult to determine on newer cold climate cultivars and so I don’t recommend using it for estimating crop yields unless you have good empirical data from your vineyard. Ohio state has a nice guide with appropriate formulas and worksheets for crop estimation.

This is a good time to apply potassium and/or magnesium fertilizers, based ideally on petiole and soil analyses from the last year or two.

Coming up: veraison and petiole analysis…

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

I’ve received questions about a couple of questions about two different yet similar insect pests: grape tumid gallmaker (GTG) and phylloxera. Both of these insects cause galls that develop around larvae that feed on foliar (and fruit, in the case of GTG) tissue which can be quite concerning, but often are not an economic threat. That said, I’ve seen vines with over 50% cluster damage from GTG, and young vines with significant leaf distortions from phylloxera that overall vine growth is likely impacted. Treatment options should be the same for either pest. Although GTG may not technically be on the label for If you decide on treatment, there are a few materials of choice, which Tim Martinson outlined well in an older post that is still relevant today. Basically, Movento is the gold standard, and Dr. Ann Hazelrigg at the UVM Plant Diagnostic Clinic recently confirmed that it killed larvae inside GTG galls from one area vineyard. Admire Pro and Assail are labeled and effective against phylloxera, but have no label for GTG.

If galling is extensive, removal of damaged leaves may not reduce the damage to the plant. Galled leaves are still photosynthesizing, and, for phylloxera anyway, hatched nymphs (“crawlers”) have likely left the galls to infest younger leaves already. As those leaves expand, expect to see more galls, but not necessarily as bad as the ones on early-season leaves. I’ve seen some pretty scarred-up leaves, especially on ‘Frontenac’, that have ripened a crop just fine. If the damage is looking too severe (and I don’t have a specific threshold), then treatment with one of the systemic materials listed above is your best management option.

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

It’s cooling off for a bit, time to think about activities in the vineyard. Thankfully, extreme heat isn’t good for most grape diseases, and the dry weather hasn’t been good for them either. However, berries are sizing up and bunch closure will be here before we know it, so we should consider some upcoming potential issues that might affect fruit quality at harvest.

First is grape berry moth (GBM). This moth lays eggs in developing clusters which hatch and infest fruit, causing direct damage as well as allowing rots to develop. Now is the time to start scouting 50-100 randomly selected clusters from throughout the vineyard and inspect for the characteristic webbing of GBM larvae, six percent infested clusters indicates a need to treat. If sprays are necessary to manage them, they need to be applied before the clusters close up. Bt is effective against GBM, as is Intrepid, Delegate (also good against spotted wing drosophila, more on that next week), Entrust (SWD as well, and organic), Sevin (good against Japanese beetles), and Avaunt (also JB). Notice I’m not recommending pyrethroids like Danitol, as they tend to be harsh on predators and may increase mite populations as a result.

Next is Botrytis. This disease is increased by prolonged wet periods and moderate temperatures (60-75° F), not what we’ve had recently. Still, if you have tight clustered cultivars (anyone still growing Vignoles?) or a history of the disease, an appropriate material may be called for if a long rainy week ever appears in the forecast. Downy mildew can infest leaves and clusters, and, like with botrytis, an effective material may need to be applied ahead of any rainy period that may come up in the next few weeks. Finally, keep an eye out for powdery mildew on foliage. If you’re relatively clean, this disease may not pose a problem for the rest of the season, but if there is incidence of the disease, it may spread given appropriate weather.

All diseases will be much better-managed with an open canopy, and your fruit quality will increase as well. Soon, if not already, the bases of shoots will lignify (get ‘woody’) and will be tough enough to comb shoots downward and separate them in order to expose fruit to the sun. This is an absolutely critical practice to attain highest quality fruit, as well as to allow for sufficient hardening off of shoots and other tissues heading into next winter. If the heat continues too much, I would avoid pulling leaves around the clusters at this time, the combing should expose them enough to develop some thicker cuticles on berries that will resist sunburn. A final leaf pulling can be debone a few weeks before veraison.

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.