Interpreting Pruning Weight Data – How to read your vines.

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By now, most of us have begun or are nearing completion of winter pruning. Many Midwest vineyards this year have been pruned in response to cold injury, but even though the pruning may be non-standard valuable pruning weight data can still be collected.

What is pruning weight data and why is it important? As a winegrower, our most fundamental task is to balance the vegetative and reproductive (grapes) growth of our vines in order to achieve the highest quality fruit. Quality in this case meaning the optimum sugars and compounds for winemaking. This study showed that there is an optimum ratio of leaf area to crop size to achieve these quality goals, but it is difficult for us to measure leaf area directly. That is where measuring the weight of one-year-old wood from a vine during pruning can give us a close approximation in the field. These “pruning weights” will give us a proxy for the size of the canopy that we can then use with yield data to determine vine balance using a ratio named “Ravaz Index”. There is a good explanation of vine balance on extension.org and more info on taking pruning weights in the Midwest Grape Production Guide starting on page 44. A few things to note about taking pruning weights:

  • Make sure to sample enough vines for it to be representative! The more vines you sample, the better picture you will have of your vineyard block.
  • By sampling three vines right next to each other from each sample location, you can try to limit the subjectivity of the vines that are chosen.

When collecting pruning weights, it is a good idea to get an approximate count of the number of canes per vine while you are cutting them off. This extra step allows you to read a few more things about the vine that may not be as easy to see with just the pruning weights. For example, if the average number of canes per vine is much greater than the number of buds left last year at pruning, then perhaps there were too many non-count shoots crowding the canopy and a consideration would be to improve shoot thinning in the following season. Additionally, by dividing pruning weight per vine by number of canes per vine you can see your average cane weight. Optimum would be around 0.7-1.4 oz; if this is low then the vines may be over-stressed, perhaps because of over-cropping or other factors, and if it is high then perhaps the vine is out of balance and didn’t have enough crop left on it. This should be considered in addition to the Ravaz Index in order to get the best idea of where the vines stand. A terrific resource for determining what your numbers should ideally be is Richard Smart’s classic book “Sunlight Into Wine” listed in the resource section of this website.

Armed with your pruning weight data, you can make data driven decisions in the year ahead. When it is time to decide how much to fertilize, you may look at your pruning weight data and decide you want to put down a bit more nitrogen in a block that ended last year weak and over-cropped. Pruning weight data reduces the subjectivity and guess work when making crop reduction decisions; using your data you can determine how big of a crop you should leave to balance the vines. By observing trends over time, you can tell if a block is in decline and take steps to identify and remedy problems.

Pruning weights are a great way to track the most foundational principle of our vineyard, vine balance. Collecting good data helps us know where a vineyard stands and how to position it to produce the best fruit in the coming season.

 

Happy pruning!

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Winter Cold Injury

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winter 2013_14

One thing about viticulture in the Midwest; you really get to know what makes grapevines tick. We have to contend with frost, too much water, too little water, and now presently….. cold temperatures!

The chart above plots this year’s high and low temps near Bloomington, IN with a dashed line to guess where the LT50 is at a given point in time. The chart below shows last year during the same period for comparison. LT50 is the Lethal Temperature for 50% of viable buds in a laboratory test. Up to about 50% damage you can compensate for when pruning, but over that number things become much more difficult. This line is only a guess because what the vine might actually be able to handle varies based off of factors like cultivar, vine health during the past growing season, crop load, temperatures leading up to spikes of cold weather, etc..

There are a few things that will be interesting to growers from these charts. First, this year we have had two periods of much colder than average weather; one early in December and the other early in January. The first one dropped near the LT50 line while the second dropped below it. These lows have the potential to cause damage especially in vines that may not have achieved their maximum hardiness because of struggles during the preceding season. In addition to the magnitude of the low temperature, the second thing to note is how precipitously the temperature dropped. While not too extreme, both of the periods were preceded by periods with high temperatures above freezing. This sudden shift can be harder on the vines than a gradual decline.

winter 2012_13

It is best to asses your vines before you begin pruning so that you can adjust accordingly. Here are two great resources to aid in evaluation:

The basic idea is to increase the amount of buds you leave in proportion to the damage up to about 50% primary bud mortality. This would mean leaving 35% more buds if you have 35% damage and twice as many buds if you have 50% damage. Once you get above 50% your focus is going to shift towards maximizing leaf area in the next season to promote vine health, and you may want to do minimal or no pruning until you can see what survived in the spring. Primary bud mortality above 50% may also signal potential damage of the woody structures of your vine, so further investigation using the above resources might help form a better picture of the damage. You may still get some crop from secondary buds and buds at the base of shoots, but over 50% this may be a bit erratic.

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The Asian Invasion

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D. Suzukii Male

Drosophila Suzukii

Drosophila Suzukii, or the spotted wing fruit fly, has made it’s way to Indiana all the way from S.E. Asia! I sighted them for my first time this past week in Monroe County. After noticing some suspect damage on grapes and finding what seemed to be larva in the berry, I consulted some of the helpful identification guides below. Sure enough, they matched the description down to the last detail. Now that I know what to look for it seems like I see them everywhere!

Although they were observed as early as 1916 in Japan, they were first sighted in California in 2008. Since then they have quickly spread across the US in our direction. Obviously fruit flies aren’t a new phenomenon but unlike an average fruit fly that is only attracted to rotting and fermenting fruit these little marauders can land on otherwise sound fruit and puncture it to lay their eggs. That capability to make an initial wound on the berry and deposit eggs that hatch into larva is what makes D. Suzukii a much bigger problem than other Drosophila.

After looking through several blocks it seemed that although they have the ability to affect sound fruit, I found them primarily in areas that had previously damaged fruit. There is quite a bit of damage from a late generation of Grape Berry Moth (GBM) that seems to have started recently and the D. Suzukii appeared to be heavier in those areas. Another block that had very little GBM damage also had almost no sign of D. Suzukii damage.

To find the SWD, I would look for damaged or rotting berries and then look for fruit flies in that area. If I could, I would look at the adults when they landed; they didn’t seem to fly away when I held the magnifying glass near them. In that same area I would start squeezing individual berries, looking for any that had a tiny leaking hole. If one was found like that, I would break the berry open and look for larva. This method was quite painstaking, so the traps that are described in the links below would be a better option for long term monitoring.

Some helpful links:

Under Trellis Cover Crops

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White Clover Under Trellis Cover Crop (UTCC)

If there is one thing we have in the midwest, it’s plenty of vigor in our grapevines. That can be a problem when it leads to an imbalanced vine and subsequent reduction in fruit quality. If this is the case, then why maintain a clean herbicide strip under our mature vines? Why not intentionally grow a cover crop under the vines or just allow native vegetation to grow in? Research done by Virginia Tech, Cornell, and a few adventurous vignerons have raised just these questions.

I am looking into the effects of this approach on a vineyard in the southern Indiana climate. The potential upsides could be:

  • Competition for water and nutrients that could help control vine vigor
  • Opportunity to modulate this competition through mowing or low rate herbicide application
  • An increase in fruit quality from improved canopy architecture
  • Reduction in erosion under the vines
  • Reduced herbicide use with related economic, environmental and health benefits
  • Improvement in soil organic matter

Potential downsides might be:

  • Controlling bindweed
  • Rodents
  • Too much competition in dry years?

Below is an outline of my current research project with UTCCs

Use of Creeping Red Fescue and White Clover to Control Grapevine Vegetative Growth

 

Introduction

Control of vigor in Indiana vineyards can be challenging. Typical rainfall totals prevent deficit irrigation techniques used in drier locations. This often results in a grapevine canopy with leaf layer numbers, shoot length, and lateral growth that is greater than that recommended for an ideal canopy as defined by Smart (Smart and Robinson 1991). Additionally, it would appear that in our vineyards excess vigor in the cultivar “Traminette” may be leading to Early Bunch Stem Necrosis and reduced fruit set. Research in Virginia has shown promise using Creeping Red Fescue Fesctuca Rubra  as an under trellis cover crop (UTCC)  to reduce vegetative growth (Hatch et al. 2011). In that study Fescue’s competition for nitrogen as well as plant available water was identified; perhaps this could be mitigated through the use of clover as an UTCC.

In this study, we will investigate whether use of UTCCs may be a useful tool to control canopy architecture. Canopy architecture has been shown to correlate with fruit quality (Smart et al. 1985, Kliewer and Dookozlian 2005.) and disease pressure (Zoecklein et al. 1992, Austin et al. 2011).  Additionally, we will investigate whether the use of Dutch White Clover Trifolium Repens may offset the demand for nitrogen by the cover crop without negating the desired devigoration.

Method

Vineyard block used in the study will be 12 year old Traminette 9ft x 8ft spacing trellised to a single non-positioned high wire and 10 year old Valvin Muscat with the same spacing and training system.

Three treatments and a control will be used in this study. Each treatment will cover one 408ft. rows. The control will be the standard herbicide program utilizing pre and post emergence to control weeds in a .9 meter band underneath the vines in rows between treatments.

Treatment 1 will be Creeping Red Fescue sown in the spring by hand underneath the vines at the rate of 6lb per 1000 ft2.

Treatment 2 will be White Clover sown using the same method at the rate of .45 lb per 1000 ft2.

Treatment 3 Will be both Creeping Red Fescue/White Clover sown separately under the same row at rates above per 1000 ft2.

The seed will be sown by hand in early spring as the ground freezes and thaws. Clover seed was mixed with dry sand to facilitate even spreading.

Point Quadrat analysis will be conducted at veraison as outlined in Smart (Smart and Robinson, 1991). Number of active growing tips and lateral development will be recorded at this time as well. Yield and pruning weight data will be recorded from the treatments at the end of the year.

Petiole analysis will be conducted at veraison to determine nutrient status of the vines during the study.

Anticipated Results

We anticipate all treatments will show an improved canopy over the control. The Clover treatment should show less of a demand for nitrogen, with the mix treatment falling between the two extremes. Effects may not be clear until the second year of the study.

Significance

The ability to control vegetative vigor in vineyards where deficit irrigation is not a reliable option could have significant impact on fruit quality and disease management.

Better control of vigor also has potentially significant economic implications. The reduced vigor would reduce the labor needed to correct the high vigor situation through leaf pulling, hedging/skirting , and lateral removal. Under vine cover crops would significantly reduce or eliminate the use of herbicide under the vines. Both of these results could improve a vineyards profit margin. The reduction in herbicides would lead to a safer environment for employees. Reduction in erosion underneath the vines would be another positive result of an under vine cover.

References

Austin, C.N., G.G. Grove, and W.F. Wilcox. 2011. Powdery mildew severity as a function of canopy density: Associated impacts on sunlight penetration and spray coverage. Am. J. Enol. Vitic. 62:23-31.

Hatch, T. A., C.C. Hickey, T.K. Wolf. 2011. Cover Crop, Rootstock, and Root Restriction Regulate Vegetative Growth of CabernetSauvignon in a Humid Environment. Am. J. Enol. Vitic. 62:3.

Kliewer, W.M., and N.K. Dokoozlian. 2005. Leaf area/crop weight ratios of grapevines: Influence on fruit composition and wine qual­ity. Am. J. Enol. Vitic. 56:170-181.

Smart, R.E., and M.D. Robinson. 1991. Sunlight into Wine: A Hand­book for Winegrape Canopy Management. Winetitles, Adelaide.

Smart, R.E., J.B. Robinson, G.R. Due, and C.J. Brien. 1985. Canopy microclimate modification for the cultivar Shiraz II. Effects on must and wine composition. Vitis 24:119-128.

Zoecklein, B.W., T.K. Wolf, N.W. Duncan, J.M. Judge, and M.K. Cook. 1992. Effects of fruit zone leaf removal on yield, fruit composition, and fruit rot incidence of Chardonnay and White Riesling (Vitis vinifera L.) grapes. Am. J. Enol. Vitic. 43:139-148.

Vineyard Timeline

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Indiana Vineyard Timeline

Click on the image to make it larger.

Close on the heals of the vineyard bursting back to life in the spring comes the fast paced craziness of all the ensuing vineyard management tasks.  Sometimes it helps to have a map of the “big picture” in order to navigate this viticultural sea. Patty Skinkis, Associate Professor at Oregon State, has created a timeline for tracking vineyard pests and cultural actions in the “Pest Management Guide for Wine Grapes in Oregon”. Inspired by this helpful format, I set out to chart a similar timeline for our vineyard in Indiana. It’s a work in progress, but it should help facilitate planning to have a macroscopic view of our major yearly concerns.

Winegrape Purchase Agreements

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Winter seems like a great time to think about purchase agreements; what better to cogitate on in the chilly pruning season than loads of beautiful grapes harvested at the end of a good year. That will warm your heart but I’d still keep the heavy winter jacket handy for the rest of you.

At the Indiana Winery and Vineyard Association meeting this past January growers expressed a desire to see some example grape purchase agreements and learn more about how these could be used here in the midwest. To this end I dug around to see what information I could collect on purchase agreements and pricing. One thing I quickly learned from what I found is that I’m not a lawyer; so if you have any lawyer buddies it might be smart to strategically appropriate a few bottles of wine in exchange for their assistance with your final document.

A couple of helpful links that I found:

The first two links are very much geared towards the west coast, but I think there is good information to be gleaned from them. It seems like good communication and getting things in writing is the bottom line to happy grower/ winery relationships.

Pricing is another thing that came up during the IWVA meeting. What are people paying for a ton of grapes? Or maybe more importantly, what should they be paying?

One established way to estimate what the value of a ton of grapes should be is the “Bottle Price Multiplier”. To use BPM you simply take the retail price of the wine the grapes are going into and multiply it by 100 to obtain $ per ton. For example, you are selling Chambourcin grapes to a winery that retails its Chambourcin for $15.00; this would mean a fair baseline price for the grapes you are selling them would be around $1500 per ton. There have been variations on this theme and allowances made for quality bonuses etc., but the delightfully simple core principle of the BPM has stuck around. Adjustments for whatever quality parameters both parties agree on would be made subsequently to this base price.

Using the concept of BPM, we can estimate what the average price per ton for a few common cultivars in Indiana might be based on a quick survey of the average retail price. The prices are from all wineries listed as having paid the $.07 gallon assessment in 2012 on the IWVA budget handout that had pricing available on the web (most of them did).

From the sample of 14 Chambourcin dry reds, the average was $16.05 with a high of $22 and a low of $10. This means that on average, a fair price for a grower of Chambourcin selling to these wineries should be around $1605 per ton or the equivalent per acre with a high of $2200 and a low of $1000. A case of $22 Chambourcin would retail for $264; assuming 150 gallons/ton and not accounting for racking/ filtering losses the grapes for that case would cost $34.92 or 13.2% of the retail price. Chambourcin rose pricing was a bit foggy, as several were blends, but the average of the ones I found was around $13.24.

Traminette poured in at $15.20 average price out of 18 wines with a high of $17.95 and a low of $14.52. The Traminette was grouped pretty tightly around the $15.00 range. So grape pricing? Average using BPM would fall around $1520 for these wines.

Chardonel settled out at $15.03 average out of 9 samples for a BPM result of $1503 average.

BPM doesn’t need to be set in stone, but at least it’s a useful tool to use when trying to determine what a fair price would be for the grapes that you put so much hard work into. Pricing doesn’t need to be by the ton, you could work out a per acre agreement based on typical yield for the block. This might be helpful in cases where the winemaker wants low yields or to make a late harvest style wine because in this scenario you aren’t being paid by the ton, but by the acre. When they tell you to drop 3/4 of the crop, you don’t have to sweat it! Other than needing to hack your way with a machete through your now out of balance vines.

For a bit of perspective on where the industry was in our region as of 2011, here is a helpful University of Kentucky survey.

I’m sure most of us would rather be pruning or racking over the latest vintage than siting around figuring up contracts and pricing, but with well thought out contracts and pricing in place we can be free to worry about other things, like trunk diseases!