In our new Know your Vines blog series we will share practical tips on what metrics to monitor in your vineyard. This is the second instalment, stay tuned for more as the coming seasons unfold!
“If you can’t measure it, you can’t improve it.”
What can we learn from pruning weights?
“Pruning weights are the most important viticultural measurement in our vineyard each year. They indicate the long term health of our vines and keep us on track.” Will Davenport, Davenport Vineyards.
We can learn a lot about the health and development of vines from the winter ritual of pruning. Recording the pruning weight from sample vines in each block is often the earliest indication of changes in the health of your vines. It allows you to understand the language of the vines, months or even years, before you can see any sign of issues.
Thanks to Will Davenport of Davenport Vineyards, Matt Strugnell of Ridgeview Estate and Frances Trappey of Rathfinny Estate for sharing their tips and experiences on this subject.
How to record pruning weight
For each vine in your sample site, place all the pruned wood in a pile and tie it together with twine, weigh the bundle of pruned material with hanging scales and record the weight for each vine into the Sectormentor For Vines app. Back in the office, the app will automatically calculate the average pruning weight for that block (or clone/variety/rootstock) and the Sectormentor Vine Health Tool will allow you to compare pruning weights and crop load between different blocks and how they are changing over multiple years.
Using pruning weights to assess long term vine health and fertiliser requirements
Vines with high vigour don’t need any fertiliser (quite the opposite), while vines with low vigour may not be getting everything they need from the soils and so might need that extra helping hand. Managing fertiliser inputs and soil health is essential to growing the best quality grapes. Of course many vineyards rely on mid-season foliar applications of Nitrogen when the vine is clearly sending out signs it’s struggling, but this is often an expensive and reactive way to manage vines. Pruning weights and compost can be a much cheaper alternative that is more beneficial for your vines, the soil and the whole ecosystem on your vineyard in the long run. Hence, increasing ecology, profitability and beauty in the vineyard.
Assessing the vigour of your vines helps understand their long-term nutrient requirements. You would think the obvious way to understand the nutrients available to your vines would be to do soil tests, however, it turns out nitrogen levels in soil tests are not a good indicator of nitrogen levels available to the vine during the growing season (read more about this here) – pruning weights can actually be a much more effective way of understanding the nutrients available to the vine over time.
Will Davenport, vineyard owner at Davenport Vineyards, monitors pruning weights from sample sites in his vineyard using the Sectormentor For Vines app. As Will told us “the simplest thing to understand about pruning weights is that it’s all about how your pruning weight changes from one year to the next. If a vine is healthy and has everything it needs it will either increase or maintain the same pruning weight. If the pruning weight in one block of vines begins to decline, that is a very early warning sign that the vine isn’t getting everything it needs. As we are organic, this early indicator has been vital for us to maintain the long term health of our vines. As soon as we see a dip in pruning weights we are able to apply compost to that block, years before any deficiencies might be visible. Identifying issues like this early is vital, as compost takes about 2 years to affect the vine’s vigour.”
In the graph below you can see the average pruning weight per vine for some of the varieties grown at Davenport vineyards from 2017-2018. It is obvious that the Bacchus New had a serious decrease in pruning weights from 2017-2018. Therefore Will and his team applied compost to just this block. It is clear that in Will’s case monitoring pruning weights has saved him time and money in the long run.
Using pruning weights to assess vine balance and vigour
If you want to compare pruning weights across vineyard blocks or different vineyard sites (e.g two sites of Chardonnay that have different planting spacing) then it helps to use a measure with comparable units such as Cane Weight and Crop Load (the Ravaz Index). As always it is not an exact science but these measures can help you to establish a standard for your own vineyard. This information and evidence can also be extremely helpful when looking to find a new buyer for grapes, or even taking on a new vineyard manager.
Looking at pruning weights combined with cane numbers at pruning time allows you to calculate the weight of each cane and therefore assess the vigour of vines across your vineyard. Cane weight is calculated from the pruning weight/cane no. at pruning. Cane weight can be used to compare vigour of similar vines on different sites, or also to benchmark vine vigour to being high, medium or low compared to other vineyard sites or blocks. With this information in mind you can decide how many buds to prune to in the future. e.g to make sure leaf growth is controlled for vines with high vigour, you would prune for more buds.
The Crop Load (indicated by the Ravaz Index), is the balance between reproductive growth (grape weight) and vegetative growth (pruning weight). It’s a useful measure that indicates vine balance and has also been closely linked to grape quality (especially sugar levels) in numerous studies. The Ravaz Index is calculated by doing the Harvest kgs/Pruning Weight. Generally it should be anywhere in the range of 5-10, but this often isn’t the case in more unusual vine-growing climates such as the UK. Instead of worrying about the standard, it is important to define your own crop load for your vineyard and, as more of us establish the optimal crop load on our vineyards, we can potentially start to define a standard for the UK.
At Ridgeview Wine Estate vineyard manager Matt Strugnell started monitoring pruning weights about ten years ago. He uses the Ravaz Index to give an indication of how balanced the vines are. Both Matt and Will pointed out that if you have an awful year with a flowering or fruitfulness issue it completely throws the ratio out as you will have less bunches but the pruning weight will remain consistent year on year. However Matt says it’s still very useful, for example he told us “in the last few years the Ravaz Index for our Chardonnay on SO4 rootstock has begun to increase compared to that on 3309, essentially the SO4 rootstock vines are still heavily cropping but the pruning weights are dropping. The vines didn’t look noticeably different but this gave us a heads up that something was changing and we need to pay extra attention to that area. We now make sure we remove a bit of fruit in early Summer and are looking more closely at nutrition for those vines.”
Matt pointed out that “even though the index will move depending on the conditions of the season (in a higher cropping year you will have a higher index) it can be very helpful to compare vine balance across different blocks within the same year, and can be an early warning sign for longer term issues before they become visible”. The team at Ridgeview do also score the cane vigour by eye – charge counting (no. of buds left on vine at winter pruning). They find the combination of the more objective pruning weights and more subjective charge count sets them in good stead for this season and the many seasons ahead.
Using pruning weights to reflect and predict
Monitoring pruning weights enables you to look back at the vigour of your vines, but also forward to what your highest yield could be. In a paper by G. Stanley Howell he describes how “in the early 1920s, Partridge proposed to use the weight of cane prunings produced in year 1 as an indicator of the upper limit of a vine’s capacity to produce and ripen a crop in year 2.” This was drawn to our attention by Frances Trappey, Vineyard Analyst at Rathfinny Estate, who started monitoring pruning weights for the first time last year. Although she got interesting results reflecting on the past growing season and vine balance, nothing directly informed their actions for this year. However after reading the paper quoted above, Frances said “This opened my mind to the value of pruning weights as both a retrospective and predictive measure. So, I will be doing pruning weights again this year, but with a different mindset”.
Pruning weights are a way of listening to your vines, not just looking at them, and vineyard managers are using this as an earlier way to sense both long-term vine health and even total potential yield for the following year. Of course monitoring pruning weights can take time and you need to be diligent with recording everything – this is where Sectormentor for Vines is your new best friend and will help save you time and money. One of the most daunting tasks, is which bits of the vineyard should I measure pruning weights from? With Sectormentor for Vines we help ensure you have specific sample bays already setup, so you only need to measure pruning weights for those vines. Using our contactless tags and smartphone app it’s easy to record the pruning weights in the vineyard as you go, no paper necessary. Finally, once you get back home all the data is already sorted and visualised for you. Our new Vine Health Indicator will allow you to immediately see changes in the long term health of vines in each block (or clone/rootstock) as well as monitor your vine balance block to block and year to year – important indicators to manage an ecological, profitable and beautiful vineyard! Please email us at firstname.lastname@example.org if you would like to use Sectormentor for Vines in your vineyard. Thanks again to Will, Matt and Frances for their contributions to this post.