How best to deal with vineyard cordon decline

Reworking for improved cordon viability

Many grapegrowers share the experience of having to deal with trunk damage and loss of production caused by vines choking on their own wire. Whether this is a result of disease or tight wrapping left over from vineyard establishment, viticulturist Sam Bowman outlines how best to approach this common problem.

Eutypa and cordon decline are an ongoing issue in Australian regions with many companies working a yearly program of redevelopment.

Whether the issue is identified as the fungus Eutypa Lata (or the closely related Botryspheria), or simply strangulation of the xylem vessels due to tight wrapping on the cordon wire during establishment, the area of viable cordon is an important issue for all growers.

If we look at a typical vineyard scenario with 1.8m vine spacing, a unilateral trained vine with a 20cm crown area and 10cm spacing between 6 spurs/buds of the wrapped area there is 140cm in gaps already excluding any additional loss caused by trunk diseases or lack of sap flow.

When calculating the loss of productive area, it can be startling to discover how much vacant cordon is in the vineyard that is still being operated as productive hectares each season.

How can I find the percentage of my cordon decline?

This is where I see the most impressive use of drone technology for the average grower.

Companies such as Southern Precision Ag (www.southernprecision.com.au) offers a drone mapping service which is very cost effective and can calculate the percentage of non-vegetative area on any vineyard. A pass in early spring when shoots are 10cm long will be a great indicator of lost spur positions.

The NDVI (Normalised Difference Vegetation Index) camera assesses the reflectance of red and NIR light in plant tissues identifying and differentiating live tissue and woody areas. When mapped along the trellised area, a great comparison and calculation can be given to determine the amount of viable and non-viable cordon. Simple.

A map of this kind can be the trigger point in a decision to remove or rework non-viable blocks when calculated back to lost kilos or tonnes of fruit. Percentage of cordon decline can also be valued by running cost with the lost percentage still requiring the same passes for operations each season without producing any financial benefit.

How does a vine become choked by its own cordon wire?

Talking with many vineyard managers across the country each year, most agree that a great deal of damage is being caused by the combination of both disease and early management factors. The idea we can just train up a vine onto a cordon and expect it to produce uniform yields each year indefinitely is a little odd, isn’t it?

I remember being taught how to roll on in my first years in the industry and being told you had to hear the cane crack to make sure you had it on properly. We have seen the effects long term, but what is happening from a vine physiological perspective?

Enter plant physiologist and Charles Sturt University (CSU) lecturer, Dennis Greer.

“The tight wrapping of cordons will contribute to the decline of the cordon.”

Greer explained that as the phloem vessels are close to where the wire will intercept the external tissues, this will limit the translocation of nutrients over time.

As the wire digs in deeper each season, it will eventually restrict the xylem and the flow of water through the vine to the leaves, shoots and reproductive structures. Often the wire will not completely limit the flow, this is why there are often dead sections between the crown and the end of the arm.

Remove or rework?

So, what is it? Remove the vineyard and start again or embark on a remediation process? Once you’ve remedied the situation, how long do you leave the cordon in place before remediating again?

This decision needs to be driven by many factors. Finances play a part in everyone’s enterprise; after all you are first and foremost running a business which needs to be viable financially to survive.

Remediation, in most cases, will limit or eliminate the need to lose yield for a number of seasons depending on the method, where removal could result in two to three years without an income.

A great example of the early success of remediation methods is the South Australian vineyard holdings of one of the country’s leading wine companies, Casella Family Brands. Casella have acquired vineyard assets in many SA regions and are no stranger to the issue of declining cordons across most regions.

South Australian vineyard manager, Peter Bird, and I caught up at the company’s Coonawarra vineyards associated with Brands Laira earlier in the year to discuss reworking and to see how their trials were progressing.

Bird explained some of the complexities: “After 25 years, all of the vineyards are at different stages of vine health and we are finding that each situation needs to be treated on a vine to vine basis”.

Their method for Cabernet Sauvignon, which seems to be the most difficult to rework due to its lack of watershoots (and their vigour) is showing some promising results in their early stages.

“We are focusing on removing most of the old crowded and necrotic wood first and just tidying up the inconsistent canopies by concentrating growth in the crown to promote new options for wrapping a new cordon,” he explained.

“We do this by removing the existing arms back to the crown with hydraulic loppers, leaving three to four long spurs, which focuses the sap flow growth for new potential arms.”

A short new cordon arm is also installed above the old cordon wire position
for additional fruit. The finding is
that each vine has to be treated individually with some pushing strong water shoots, which are then trained up to replace the existing cordon and, where possible, some simply wrapped from the new growth in the crown, showing positive results.

“It’s a three-year exercise, but we are rewarded with fruit each year to compensate the cost,” Bird said.

As Cabernet Sauvignon is less vigorous, beheading the vine can result in mortality more often than Shiraz, which will push strong options for rework.

Retaining the area of growth around the crown maintains the flow of nutrients through the vine, which Bird has found will support all of the options from watershoots and below the crown area.

“This is a time consuming and expensive process but we have proved it is possible and believe we are returning some value to the vineyards and improving their viability in the long term,” Bird concluded.

Whether cordon decline is caused by a trunk disease or a carryover from establishment, it’s great to see companies and growers of all sizes tackling the situation head on and sharing their experiences.

In this new phase of the Australian wine industry, we will need all the functioning cordon we can get.

The author would like to thank Casella Family Brands and Peter Bird for their contribution to this article.