New Zealand Winegrowers’ Virus Elimination Project has just completed another season of trials, workshops and related activities. This post will provide an update on work leading up to the 2013 harvest, but first, we want to acknowledge the efforts of all the growers and viticulturists who are participating in the research and following our protocols for the management of Leafroll Virus 3 and its main vector – mealybugs.

The control and elimination of Leafroll 3 is a community issue. That’s one reason why our project is experimenting with social media channels such as this blog. Our hope is that the easier it is to access information materials (and to share them), the easier it is to “walk the talk” where it counts – in the vineyard. We always welcome your comments: they help to guide us in the preparation of new materials and the refinement of our key messages.

To assist growers with pre-harvest symptom monitoring, we created another social media channel on Flickr containing sets of photos showing symptoms on different varieties. To date, the library has received more than 2,000 views and can be accessed via this link.

Following our recent workshops in Hawke’s Bay and Marlborough, it has become evident that awareness concerning mealybugs and their role in the spread of Leafroll 3 Virus has greatly increased among growers. Key team members have fielded phone calls and emails from individuals who have discovered the presence of the vector in their vineyards this season. Numerous questions relating to the "allowability" to apply post-harvest mealybug controls prompted us to distribute an email to all growers, outlining our recommendations on how and when to apply controls.

All the fact sheets on managing Leafroll 3 Virus can be accessed from this page (see the box on the lower right) and from the main Research area of New Zealand Winegrowers’ website.

2013 trials – what we did

Mealybug monitoring, conducted by our partners at Plant & Food Research (PFR), was expanded in the Marlborough region to include the deployment of 100 pheromone-baited traps with the assistance of volunteers from the grower community.

PFR also expanded the vine leaf assessment programme from the current 8 vineyards to include a further 15-16 Marlborough vineyards. The expectation is that selected sites will be widely distributed across the winegrowing region, allowing a more robust assessment of mealybug species composition and greater insight into their spatial distribution.

We completed the initial set-up and mapping of four Sauvignon Blanc and four Pinot Noir trial blocks in Marlborough to assess current infection levels. The mapping will be continued over the next two years, providing a complementary data set to that collected in the Hawke’s Bay region. An initial visual identification of symptoms was completed on the Pinot Noir blocks as was ELISA testing of samples collected from the Sauvignon Blanc blocks.

Our white-variety (non-symptomatic) screening trial sampled 200 vines per block, with follow-up ELISA testing – first in composites of 20, and then in composites of 5. The results show excellent correlation, and we are confident this methodology can be used as an industry standard to assess infection rates in white-variety blocks.

The 2013 harvest and yield data have also been collected from six positive (infected) and six negative vines from three of the Sauvignon Blanc trial blocks (the fourth block had such a low level of infection that data collection wasn’t required).

Our project team also assessed the indicator grafting trial for visual expression of Leafroll 3 Virus on white varieties. Leaf samples (2 leaves per vine) were collected from all of the vines in the trial and leaves were sent to Linnaeus Laboratory for ELISA testing. A comparison will be made between visual identification and ELISA test results to gauge the accuracy of the grafting technique in detecting the presence of the virus. All vines showing visual symptoms were also tagged and GPS-marked.

The ongoing mapping of Leafroll 3 infections across the Gimblett Gravels started in early March. With a short, sharp and early harvest, growers were able to get onto virus identification earlier than usual. As a result, we have already mapped 80% of the area and expect to complete the remaining 20% in the next few days. This data will be collated and maps created for individual growers and the wider area. These numbers will then be compared to previous years to monitor the incidence of virus and the trend or reduction of spread occurring, which will be quantified by the project team.

Our instructional videos are also nearing completion, having been filmed at the appropriate growth stage for each major step in Leafroll 3 control. Once leaves on vines have senesced, we’ll be able to complete the remaining segment and prepare the videos for review and distribution to the industry.

All in all, it’s been a busy – and gratifying – year for the Virus Elimination Project team, and we’re looking forward to analysing and then sharing all the information we’ve collected in the months to come.

In recent weeks, the Virus Elimination Project team has visited a number of growers who have experienced some difficulty with regard to monitoring for symptoms of Leafroll 3 Virus on red varieties in their vineyards.

The growers have found it difficult to discriminate between symptoms of magnesium deficiency and Leafroll 3 – a topic that is covered in some detail in a previous post that can be viewed here.

This has proven particularly troublesome where vines have been grafted onto S04 rootstock: leaves may still express symptoms of magnesium deficiency, but the colouration is similar to the darker reds often shown when Leafroll 3 infection is present. Magnesium deficiency shows:

• Red wedge-shaped areas on leaves, extending inwards from the leaf margin between the main veins. The colour change is not parallel with the veins – this is a clear difference from Leafroll symptoms.
• Broad areas of green remain around the main veins.
• The leaf margins may turn brown.
• Dead patches may develop in the red areas and at the leaf margins when magnesium deficiency is severe.

If you suspect that vines are expressing symptoms for magnesium deficiency, it’s worth referring back to any leaf-petiole analysis that may have been done at flowering to see if test results confirm your suspicions. Consider the vineyard as a whole: based on your previous monitoring for Leafroll 3 symptoms, is the vineyard showing a large increase in colouration this year? If so, is it likely that some of these symptoms might represent a nutritional deficiency instead of rapid spread of the virus?

Both leaves indicate the classic wedge-shaped symptoms of magnesium deficiency, but leaves may not always show the reddish-orange tones on the left. As leaves start to senesce, colours may change to darker reds (shown on the right) that are similar to colour symptoms for Leafroll 3. The area of colouration, however, remains wedge-shaped, indicating magnesium deficiency.

Test to confirm your observations

Where symptoms for Leafroll 3 infections are not clear cut, it’s always advisable to send leaf or cane samples in for laboratory testing. Testing for Leafroll 3 requires an ELISA test (approximately $15 per individual test) and is a cost-effective tool in your virus management programme:

• If a result is positive (that is, if Leafroll 3 Virus is present), the test will help you to calibrate your ability to visually identify and differentiate between symptoms.
• If a result is negative (Leafroll 3 Virus is not present), one or more vines are saved.

Given that removing – roguing – a single individual infected vine represents a minimum loss of $45 in the vineyard (a conservative estimate that does not include flow-on losses in wine production), the cost of testing is moderate by comparison.

Growers often find that their ability to easily recognise Leafroll 3 symptoms develops over time. Sending in a few samples for testing during the first year or two of monitoring provides valuable corroboration for visual identification in subsequent seasons.

Visual guides

Don’t forget about our photo library on Flickr, which provides images of symptom expression for Leafroll 3 Virus and magnesium deficiency and can be viewed here.

New Zealand Laboratories

ELISA testing is offered at the following New Zealand laboratories, all of which will provide instructions on sample collection and delivery.

Leafroll 3 Virus symptom development on Syrah.

Each year as harvest approaches, the Virus Elimination Project fields calls and emails from growers asking for more details about symptom expression of Leafroll 3 Virus in red varieties.

Recognising symptoms takes some practice, and it’s important to confirm your suspicions by sending leaf or cane samples for laboratory ELISA testing in the first season of monitoring.

To help you develop your ability to detect symptoms, we have collected photographs illustrating Leafroll 3 expression on individual red varieties, including:

• Pinot Noir
• Merlot
• Cabernet Sauvignon
• Syrah
• Malbec

These photos, plus other sets illustrating magnesium deficiency and the difficulty of spotting symptoms accurately on Sauvignon Blanc, can now be accessed at Flickr, which houses the new image collection published by New Zealand Winegrowers Research. 

The sets are easily viewed on mobile devices, so it’s worth bookmarking the link on your smart phones and tablet computers so that you can use the references in the vineyard.