Frequently Asked Questions for Pruning Grapevines

By: Annie Klodd, University of Minnesota Extension

Pruning season is almost upon us, this article references common grapevine terminology and requires the reader to have basic knowledge of grapevine pruning. If you are new to pruning, take some time to familiarize yourself with grapevine structure and the basics of pruning.

Does it matter when I prune during the dormant season?

If you would like to do some light pruning before the first big snowfall, feel free. If you prefer to wait for sub-zero temperatures to prove something to yourself, that is fine too! Just wait until the vines are fully dormant and the leaves have fallen before you start pruning.

Pruning in the coldest months has an upside. It minimizes the risk of diseases infecting the pruning cuts. When temperatures dip below about 35 degrees F, fungal diseases of grapes are not actively spreading. If you prune early, it is best to do a “long prune.” Leave extra length on each cane in case a severe cold event causes bud damage later on.

Additionally, leave a couple of centimeters of wood past the last bud – cold, dry wind can desiccate the wood at the pruning wound.

Late pruning in March and April is certainly more comfortable than deep winter pruning. However it also means you are pruning when fungal pathogens are more active. Be aware that fungal trunk disease pathogens are more active during the spring and will readily enter the wood via those pruning wounds.

How do you decide how many buds per spur to leave during pruning?

The general rule of thumb is to cut each cane down to a 2-3 bud spur. This assumes that all buds are healthy and that the cordon contains one spur every 3-5 inches. If this ideal scenario does not exist on a vine, you can either alter the number of buds per spur or the number of spurs per cordon to account for imperfections.

In cold climates, winter damage usually kills some percentage of the buds on a vine. It is helpful to estimate the percentage of dead buds and adjust your pruning to make up for bud loss.

To measure bud mortality, take a representative sample of canes throughout the vineyard and dissect their buds with a razor blade. The color of the bud’s interior indicates whether they are alive or dead. Buds that are green inside are healthy and will grow into shoots. Buds with brown interiors have died.

Remove between 20-50 normal canes from throughout the vineyard. Bring them inside to room temperature for 24 hours. With a sharp, slim, and clean razor blade, carefully slice off the tip of each bud in the first and second positions along each cane. The bud contains 3 parts – the primary, secondary, and tertiary sections. The primary is the middle and largest section, and it produces the most fruitful shoots. Record whether the primary section of each bud is green or brown (alive or dead), and repeat this with 100 buds. If 10-15% of primary buds are dead, do not adjust your pruning.

If 20-40% are dead, leave about 25% more buds than you typically would. If 40-60% dead, double the number of buds you keep. If more than 60% are dead, do minimal pruning, leaving 5 buds on each spur.

Very long spurs are cumbersome – the longer the spur you leave, the higher the chance that only the buds at the very top will break. This is due to a concept called apical dominance. Excessively long spurs also creep up out of the regular fruiting zone, interfering with the structure of the vine. To avoid spur creep while still leaving extra buds, you may instead leave a higher number of 2-3 bud spurs.

Should basal nodes or “non count buds” be accounted for during pruning?

In cold climate hybrid grape growing, yes. In Vinifera vineyards, no.

A basal bud is the bud at the base of the new spur wood. In other words, it is located at the point where the 1-year old part of the spur meets the 2-year old wood.

When it comes to cold hardy hybrid grapes like Marquette and Frontenac, the basal buds are usually fruitful. In fact, they can sometimes be the most fruitful bud on the whole spur. Most of them will carry two cluster per shoot. But this is not the case on vinifera and French-American hybrids, where the basal buds are just vegetative. While the traditional recommendation, which arose from Vinifera vineyards, is to not count the basal bud during pruning, this recommendation is revised for cold climate hybrids where they should be counted. If you leave a basal bud plus two more buds, you will have up to 3 shoots per spur.

Some of my vines are getting old, and I notice that parts of their cordons are missing spurs and canes. What should I do?

We call these empty spots along the cordon “blind wood.” Blind wood happens when old spurs die, and no new buds form from the cordon to replace them. One thing that causes blind wood is winter injury, so it is common in cold regions. Winter injury accumulates over time, so older cordons tend to have more blind wood than newer cordons. In cold climate grape growing, we recommend replacing cordons once they start showing blind wood.

To replace a cordon, first find a healthy new cane that is growing from the base of the cordon or the middle of the vine along the wire. Lay the new cane down alongside the existing cordon, and tie it to the wire. Clip off the end of the cane where the wood is very skinny so that only the healthiest wood remains. If the old cane is totally unproductive, remove it at this time. If it is still producing some fruit, you have the option of leaving it in place and growing the new cordon alongside it, as long as the vine is vigorous enough to support both.

What if the whole vine has died back to the ground level?

Extreme dips in winter temperatures sometimes kill the entire aboveground part of the grapevine, including the cordons and trunk. This is even more likely if the vines are stressed going into the winter, either from drought or wet feet. Rest assured that even if the trunk and cordons are dead, the roots are usually still alive and can re-grow a new vine.

If you grow “own-rooted” (non-grafted) vines like University of Minnesota cold hardy hybrids, you can re-grow the vines from suckers rather than planting new vines. Start by cutting the dead or dying trunk back to the ground level. If suckers are present, choose 1-2 of them to become the new trunks. If the vine was particularly vigorous before it died, you may want to keep extra suckers so that the excess energy from the roots has somewhere to go. The extras can be removed during or at the end of the growing season.

After selecting the suckers that will become your new trunks, prune them back to the point where the wood becomes thicker than pencil diameter. The reason we do this is because the thinnest wood is the least productive and has a high chance of dead buds. Keeping only the healthiest wood helps those vines produce vigorous new trunks and cor(Continued on Page 52)

(Continued from Page 50) dons. There is no need to cut the cane back to a 2-bud spur. For example, if the first 4 feet of the cane are healthy and thicker than a pencil, then make your cut 4 feet off the ground.

Should I prune out small pieces of dead wood like old spurs?

If time permits, pruning out dead spurs is a good idea. They can harbor spores of diseases like powdery mildew and phomopsis that re-infect the vines in the coming season. Pruning out dead wood is one good non-chemical disease management tool.

What is the liquid coming out of the pruning cuts when I prune in the spring?

That liquid is sap! This is a sign that the vines are exiting dormancy. Sap runs through the vines as the soil warms, so that the buds can start actively growing. It is time to wrap up the pruning as the vines “wake up.”

What is a bull cane?

A bull cane is an exceptionally thick, long cane with very wide spaces between buds. They grow more aggressively than regular canes, often growing into the next vine and beyond. Rather than being round, these canes take on a subtle oval shape. They tend to be less winter hardy and less fruitful than normal canes, so they should be removed. If possible, do not use bull canes to establish new trunks. Bull canes tend to grow if the grapevine is too vigorous, such as when a vigorous variety is grown on rich, moist soil.

How do you remove tendrils from the wires?

My best advice for this is: Only have as many wires as you need to trellis the vines. More wire means more tendril magnets. For example, on a Single High Cordon trellis system only one wire is necessary. Do not string any other wires lower down.

For a deeper dive into these Frequently Asked Questions, watch our recorded webinar from the Cold Climate Fruit Webinar Series:

https://www.youtube.com/watch?v=k6slKtnnt2o&list=PLcXxBuLJhm43w6qZxoiw7DjHxxsNw3qUu&index=3&t=1s

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The Cape Crusaders of PIWOSA

By: Tod Stewart

Challenging perceptions - and righting misconceptions - typically isn’t an easy thing to do. This is especially true when attempting to raise the stature of something generally not held in particularly high esteem. Until fairly recently, the wines of South Africa tended to be passed over by all but the most knowledgeable wine types - at least here in Canada (but I suspect in other parts of the world as well). Thankfully, this situation has changed considerably - largely due to the quality of the wines themselves and the efforts of dedicated winemakers continuously looking to improve things. I dub these folk “Cape Crusaders,” among them, the members of the Premium Independent Wineries of South Africa (PIWOSA for short) are some of the most heroic.

Though these guys and gals are superheroes of the wine world, they were wearing jeans rather than spandex (as was I, so let’s get that cleared up right away) when I met up with a few of them in a Toronto bar a while back. Their mission isn’t ridding the world of crime but rather ridding it of ignorance, preconception and overt cluelessness. All in the name of South African wine. Gesundheit to that!

how the wines of South Africa - and the industry itself - should look.

“It was a combination of a lot of years of frustration,” admitted Alex Dale from Radford Dale (and also the PIWOSA co-founder and director), who shared a glass or two with me along with Paul Clüver of the eponymously named Elgin Valleybased Paul Clüver Wines and Bruce Jack, from the Drift Farm in the Overberg Highlands. “Of all of us traveling around the planet, going to the shows, working with importers, doing our bit, we realized that the reputation of South African wines, in many markets, was being driven by wines on the low end of the scale. This isn’t South Africa - especially not South Africa today.”

Of course, guiding consumers to the best wines South Africa has to offer assumes, to a degree, that they even know much about the country’s wine industry. It could be a bit of a shaky assumption, at least as far as the market for South African wines in Canada goes.

“South Africa remains a largely unknown winemaking country in Canada. It is geographically very far away, so quite fairly, many people have not visited; therefore, their frame of reference is limited,” suggests Laurel Keenan, the manager of Wines of South Africa (WOSA), Canada. “That in and of itself can be a big obstacle. The second is the amount of shelf space we are generally afforded in retail stores, which is quite small and sometimes hard to locate. For a long time, the selection was also not reflective of the best wines produced there, but that is slowly changing.” It’s also worth remembering that sales of South African wines and spirits were impacted by global anti-apartheid sanctions imposed in the mid-1980s that were not lifted until 1994, meaning that once they were lifted, the industry required a huge “re-education” effort.

People like Dale and the rest of the PIWOSA contingent realized that if a change were to be accelerated, they would have to, in Dale’s words, “roll up our sleeves and do it ourselves.” With no government funding, the member wineries had little choice but to crack their collective piggybanks and pool their resources. “Either we clubbed together to make a difference and make it happen by ourselves, or it wasn’t going to happen at all,” Dale emphasized.

One might wonder (okay, I wondered) how this “club” of 10 wineries (today 12 as a couple of new member wineries have since jumped aboard) in a sea of about a thousand in South Africa can hope to have any impact on the global market. Clüver is quick to point out that PIWOSA represents the “super-premium” tier of South African wines. In other words, the wines that fall into the price bracket noted by Keenan are where the real “bang for the buck” starts to be realized. And while there are other South African winery associations in operation, none, in Clüver’s eyes, “are as committed to the process or as organized and active as we are.” However, he is emphatic that PIWOSA member wineries aren’t the only ones producing fantastic wines at what he says are “ridiculously low prices.”

Ridiculously low prices can be a bit of a double-edged sword. Though I would be the first to agree that its top-tier wines are largely undervalued, the “cheap and cheerful” image of South African wines may have created a misconception among consumers that this was all the county’s winemakers had to offer. And trying to work from the “bottom up” is no cakewalk. If you get into the market on the high end, it’s fairly easy to work down (look, in no disparaging way, at what Robert

Mondavi did - reportedly personally disfavourably - with the Woodbridge brand). It’s not so easy going the other way.

“The South African entry into the major market, after 1994, was never from the premium end. It was always volume, always commodity, always the lowest common denominator. So our collective mission, our task, is to eliminate old preconceptions and raise the bar. A lot of sommeliers are very Euro-centric with their wine lists and perceive South African wines in a way that is completely inaccurate. We want - and need - to change this, and the impact we can have as a collective is exponential to what we could do alone.”

I touched base with Dale recently to get an update on PIWOSA and where things currently stand visa-vis the quality and perception of South African wines. What he told me was refreshingly positive. “In many places, it is day and night compared to 10 years ago,” he enthused. “Gone are the days when you needed to hear references to burnt rubber and critter labels at every turn. We are welcomed today just about everywhere, taken seriously and listened to. Sure, it’s not like selling Burgundy, but we have made enormous strides, and PIWOSA has been very much at the forefront of this, notably in the UK, Canada and across Asia.”

Of course, the industry today faces challenges that were likely unexpected when PIWOSA was initially established. Climate change and prolonged drought are two major impacts on South African winegrowers.

“The change in climate coupled with the sustained drought we experienced in 2016, 2017 and 2018 along with the ongoing lack of a reliable supply of electricity got many of us thinking - and some acting! Many wineries have implemented significant water efficiencies as well as energy- generating initiatives, whether emergency-type fixes with generators or much more sustainable, long-term shifts in introducing solar. There has been a realization that in agriculture, we can’t just carry on as before. Although not yet widespread, some of us are converting or have converted to organic production (Radford Dale included, as our Estate in Elgin is one of only and handful in South Africa to be fully organically-certified).” winemaking styles, Dale stated, “There has been a generational shift away from the sorry era of Parkersied wines and the big/powerful-is-beautiful thinking. Interestingly, this transition plays directly into the handbook of PIWOSA, where we have always advocated balance and greater authenticity in our wines. Also, we’ve seen the emergence of a young and diverse generation of very aware, passionate and capable winemakers, and this is possibly the most exciting development in the South African wine industry. We really have a hotbed of talent and energy here right now.”

PIWOSA’s commitment to excellence goes well beyond the crafting of top-quality tipples.

“Our ethics charter was pioneering in the industry. It committed each member to the highest levels of integrity, employee-welfare, ecological best-practises and so forth, long before these subjects came under the spotlight and global scrutiny, as they have in recent years. There is certainly more attention to these matters in the industry now, generally, which has got to be a very positive development. Lastly, I think the resilience we have demonstrated as an industry, over the COVID era, has shown just how strong we can be. Not only did our government try to put us all out of business and fail (with multiple bans on the sale or transport of wine, initially in both export and domestic markets), not only did we receive zero financial support, grants, tax-relief, employee support or any other COVID-related funding, but we ended-up selling significantly more premium South African wine internationally, as consumers around the world rallied to help us in the face of what was plainly an unjust targeting of our industry, for political reasons, with no connection to the pandemic whatsoever. As Nietzsche said, ‘What doesn’t kill you makes you stronger.’ It certainly has!”

As a winegrower, you know that the best quality fruit usually comes from vines that are resilient, adaptable and, well, pretty stressed. Considering what the vignerons of South Africa have gone through over the years, perhaps these factors result in top-quality winemakers as well.