By Sam Bowman
A year ago, in the March 2017 issue of Grapegrower & Winemaker, viticulturist Sam Bowman revealed the importance of post-harvest vineyard management and the reasons why it should be a consideration as much as nutrition, irrigation and fungicide programs during the growing season. Now, he explores the topic further by presenting a round table discussion with some of Australia’s leading lights of viticulture. He asks about what works best for them once harvest has taken place.
Understanding the physiology of the vine and the dependence on stored carbohydrates helps reduce biennial bearing and brings consistent patterns of growth each year (weather dependant of course).
Australia is lucky to have some brilliant minds in viticulture across our vast and differing landscape.
We have called upon some of our top viticulturists to offer insights into how they manage their vines after the grapes have been picked and begin the journey to becoming another bottle of great Australian wine.
Contributors taking part in this round table discussion:
Gina Knight (GK) is vineyard manager at Coldstream Hills, Upper Yarra Valley Vineyards, Victoria
Liz Riley (LR) is a viticultural consultant based in the Hunter Valley, NSW
Hannah McKay (HM) is vineyard supervisor at Vasse Felix, Margaret River, WA
Jenny Venus (JV) is senior viticulturist, Landmark, SA
Q: How do you manage irrigation after harvest and how is the irrigation regime monitored (soil moisture probes, visual canopy identifiers, soil inspection)? Typically how many days/weeks would you continue to irrigate after harvest?
GK: Fortunately, we generally have sufficient water at the end of the growing season to be able to irrigate for around three weeks after harvest giving the vines around 8 to 12L each per week. We use a dig stick to assess soil moisture.
LR: Given that we usually have harvest rain or post-harvest rain, the need to irrigate is really driven by the weather. Currently we have very dry conditions and ideally post-harvest irrigation would be going out. We are going to have a 12-16 week post-harvest period so it would be good to both retain the current canopy but to also push some fresh leaf to generate some additional carbohydrate reserves to rebuild the vines after the tough season. The ‘new’ canopy needs to be pushed quickly and have time to mature and contribute back so through Feb and early March, rather than later in March and April which is too close to dormancy commencing.
HM: In terms of scheduling irrigation events, given Margaret River is historically so dry during the harvest period and vineyards restrict water supply for the final push before the pick, it is good to give the crop a drink the night or early morning following the pick. This also ensures maximum utilisation of the water application and transportation within the vine as it will be absorbed quickly and not be used in fruit maturation or acid dilution.
JV: After harvest, the vines are irrigated to refill the profile to allow them to recover from the stress of harvest. Often vines, particularly red varieties are water stressed leading into harvest to develop intense flavour profile. Once harvest is complete it is important to refill the profile to ensure the vines are able to adequately store carbohydrates to next season.
Do you have a requirement to continue a fungicide programme after harvest and if so which pests/diseases cause issues?
GK: This is rare, however the only fungicide we would use after harvest would be sulphur if there was a late powdery infection or mite issues.
LR: Yes – with a 12-16 week post-harvest period where canopies are present we tend to go out with a copper, sulphur and caterpillar control spray. This may be repeated if there is sufficient new growth to warrant it and will also be applied to growing young vines.
HM: Historically the most common target for post-harvest fungiciding in Margaret River has been Botrytis with this year showing a small pressure of powdery mildew. Potassium silicate sprays are becoming the hot topic in the region as we are seeing a strong shift towards organic viticultural practices. These products strengthen the plant cell walls protecting them from further disease manifestation and penetration.
JV: If scale and mealybug are present in the vineyard, there may be an opportunity to apply an insecticide spray to control some of these insects prior to them migrating under the bark for winter. Scale and mealybug are becoming an increasing problem in many regions and they are often difficult to control in season, therefore it is important to have a post-harvest/winter strategy as well as an in-season program to keep on top of insect pests.
What does your post-harvest nutrition programme look like? What are the main elements you are looking at getting in before leaf fall? Any products you swear by?
GK: As soon as possible after a block has been harvested and depending on availability of tractors and people, we spray a foliar spray containing a mix of nitrogen, calcium, magnesium and boron, while the leaves are still healthy and active. We believe the combination of these elements improves the uptake of nutrients and their movement within the vine.
LR: Depends on the site – nitrogen and potentially potassium and phosphorus subject to petiole results and field symptoms. The decision to apply, formulation (solid/liquid), method (foliar/fertigate/undervine), products vary according to conditions – we are nimble and often have more than one plan up or sleeve.
HM: Many think that organic and biodynamic farming is too costly to implement large-scale, but there is something quite primal and resourceful to it. We are seeing that in our vineyards with more sites producing their own nutritional requirements. An example is the age-old use of compost that is raging in the region at the moment and showing real strength in short and long-term benefits. Utilising grape marc from winery presses not only closes the system between vine to wine and then back to vine but also provides a brilliant upcycling of quality plant material.
JV: Generally, I recommend growers fertigate phosphorous and if possible also apply a seaweed type product to help with uptake. I prefer to manage the vineyard floor not just the strip below the vines. Growers should be considering cover cropping and broadcasting fertiliser and gypsum as another way to improve the overall health of the vineyard.
Any other post-harvest tips or tricks you have had success with in your career?
GK: We keep watering as long as we can after harvest and try to ensure we replace at least some of the nutrients the vine has lost through harvest. If this can be done, we believe the vineyard will benefit the next season when the vine has all the stored carbohydrates ready and available for the new season.
LR: Keep looking at vineyards, make plans in two week cycles and adjust subject to change. Most importantly have a break, recharge and refresh.
HM: Most non-grape or wine folk think that as soon as the fruit is off, vineyards shut down but for most growers you take a moment and bask in the glory of getting all or most of the fruit across the line and then start implementing good foundations for the following grow season. Naturally everything in vineyards is about timing so with no rest for the wicked; happy harvesting but make sure you show some managerial love post-harvest to the vines that have worked so hard to produce such good fruit to continue the legacy of great Australian wines.
JV: Post-harvest is a great time to see what has happened through the season and how the vines have grown. Once the leaves have fallen it is easy to see the vine structure, the strength of the canes, where the bunches were distributed on the vine (as long as they weren’t hand-picked). Grower should take some time to assess the vineyard post-harvest, dig some soil pits, take soil tests and plan to mulch weak areas or prune stronger areas differently. Sheep have become part of the winter management program but cover cropping is also important and helps improve the entire vineyard floor. Consider locking sheep out of some blocks and cover cropping to help manage weed problems, improve soil health, vine vigour, etc. Post-harvest should be a time to reflect on the season and plan for the next season before the grower gets busy with all the winter jobs.