University of Vermont

By Terence Bradshaw

Pardon my absence these past few week- a trip to beautiful Istanbul, where I presented some of our research from the past couple of years on cider apple management, and both wrapping up and starting a new course have kept me a bit distracted. Grapes in Vermont vineyards are some of the best quality I’ve seen in recent years, as that dry summer facilitated low disease pressure and fabulous growing conditions. Veraison has come and gone, hopefully all who need it have bird nets up and are now starting to arrange the logistics of moving that fruit into ready fermenters (or customers’ baskets, for the table grape growers out there).

As harvest approaches, it is critical to track ripening in the vineyard to best achieve the juice chemistry values to optimize wine quality. 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. Berries should be randomly selected, but should come from a diverse distribution in the vineyard: from all parts (top, shoulder, bottom) of the cluster, and from clusters well-distributed through the canopy. Fruit can be collected into a plastic bag, crushed lightly, then a corner of the bag cut off to squeeze juice into a sampling jar. Juice should then be assessed for pH, sugars, and titratable acidity (TA). 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.

Dr. Imed Dami at Ohio State has a good fact sheet on evaluating grape ripeness at: http://ohioline.osu.edu/factsheet/HYG-1436

Sugar level and pH are easily evaluated with simple tools (a refractometer and pH meter, respectively) available from most winemaking supply outlets. TA test kits are typically available from the same vendors. A procedure for measure TA through titration is available at: http://www.extension.iastate.edu/wine/titratable-acidity

It’s not too late to perform petiole sampling, which is the best method for assessing nutrient status in plants. I’m copying my instructions below from a previous post, as that information is still relevant:

Petiole sampling
Growers may ascertain overall nutritional status in their vineyards at two times through petiole analysis: bloom and 70-100 days post-bloom. Now is the time for late (post-veraison/pre harvest) petiole sampling for plant nutrient status. Dr. Joe Fiola form the University of Maryland has posted some good recommendations in his latest Timely Viticulture newsletter:

· Grape petiole analysis is recommended along with soil samples and visual observations as part of a complete nutrient management program.

· A three year cycle of sampling all of the varieties in a vineyard is typically recommended.

· Tissue/petiole analyses reveal the actual nutrients in the vines.

· Spring tissue sampling is a good time to sample, as you can make nutrient adjustments to the vineyard that will influence this year’s crop quality.

· Nitrogen status is best evaluated with tissue sampling not soil sampling.

Some specifics on sampling:

· Each sample should be less than 5 acres; less if there are major changes in soil or topography

· Sample different varieties separately. Samples should represent plants that are planted on the same soil type and are of the same age, variety and rootstock.

· Vines should represent that portion of a block that is maintained under the same cultural practices, i.e. fertilizer, irrigation and vigor control practices. For example, irrigation blocks are not to be combined with non-irrigated blocks even if they are on the same soil type.

· Do not sample vines on the border of the block or near dusty roads.

· For the late-season sampling period, sample the petiole of the most recent- FULLY EXPANDED leaf (NOT the one across from the first blossom cluster as during bloom).

· About 75-100 (depending on size) petioles are needed as they are typically smaller at the end of the shoot.

· Gently wash petioles with water and gentle detergent, pat dry and place in OPEN paper bag (lunch, #6 size) to dry for a few days.

· The closest analytical lab for grape petiole analysis is Dairy One, which is affiliated with the Cornell Nutrient Analysis Lab. It is recommended that you contact them before you send any samples to confirm that recommendations will be sent along with the analysis and to confirm costs.
Video about petiole sampling: https://www.youtube.com/watch?v=8EHbojLfXek

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 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

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.