ITHACA, NY – Removing not just one diseased vine, but also the two vines on either side, can reduce the incidence of leaf curl disease, a long-standing blight of vineyards around the world, found researchers at Cornell University.
Leafroll disease, a virus transmitted by scale insects, damages vines, reduces yield and impairs grape quality – all of which can negatively affect wine quality and cost growers tens of thousands of dollars per hectare. There is no cure for leaf curl disease, so growers have traditionally attacked it by ripping out infected vines – that is, removing or removing “rogue” plants – and replacing them with healthy plants.
In the first study of its kind, Cornell AgriTech scientists have documented that the new technique, called spatial scrubbing, can reduce the incidence of leafroll disease in commercial vineyards. Removing the extra vines eliminates means of transport for the mealybug leafroll virus, creating a gap-like space. The study was published in the April issue of the American Journal of Enology and Viticulture.
For the study, Marc Fuchs, a professor in the section of Plant Pathology and Plant Microbe Biology in the School of Integrative Plant Sciences at Cornell AgriTech, and his team planted a plot of Cabernet Franc at Sheldrake Point Winery in Ovid, New York, where they documented the presence of leafroll disease and mealybugs, then tested the effectiveness of spatial scrubbing and management of insecticides against mealybugs, alone and in combination.
Over a five-year period, they found that space scrubbing was effective in rapidly reducing the incidence of leafroll virus – from 4% in 2016 to almost zero in 2020-21 – while the viral incidence of unstemmed vines increased from 5% to 16%. Insecticides reduced the mealybug population to almost zero during the same period; in the untreated vines, it increased from 57 to 257 times more. But insecticides have not been shown to limit the number of newly infected vines.
“Dealing with leaf curl was a bit like a ‘mole hit’ game because it kept popping up,” said Dave Wiemann, vineyard manager at Sheldrake Point Vineyard. “By acting quickly and using Fuchs’ strategy, we now know that we will avoid having to remove large sections of vineyards in the future. This will result in more consistent yields and quality, both of which are critical to the success of our vineyard.
Fuchs has been studying grape viruses for decades and was intrigued by the possibilities of spatial scrubbing. But it wasn’t until 2015, when he collaborated with Miguel I. Gómez, Robert G. Tobin Professor of Food Marketing at the Charles H. Dyson School of Applied Economics and Management, and Shadi Atallah, his graduate student at the time he was able to pull together some numbers to back up his case.
“They modeled what they call the bio-economic spread of disease, where you take into account how the disease spreads in the vineyard and what the economics have been for the grower,” said Fuchs. “That is to say, do you remove a single vine or also the two adjacent vines, and how much money do you gain or lose? When is it more economical to do one thing rather than another ?”
Spatial roguing comes at a cost, Fuchs said, in terms of the labor required to remove diseased vines and replant with healthy vines, in addition to the loss of full production during the five years it takes to a new vine to start producing.
“Growers are used to making business decisions about how best to run their vineyards based on immediate profits,” he said. “But we are convinced that it is worth losing some money up front, or investing money up front, because the dividends would be incurred much faster down the road.”
Sometimes the leafroll infestation can be so high – a viral incidence of 25% or more – that it is not economical to employ space scrubbing. In these cases, some growers will choose to do nothing and live with the reduced quality of their grapes, while others will determine that total replanting of the vineyard is the best strategy.
The concept of spatial scrubbing may confuse some grape growers and grape growers, Fuchs said.
“Producers like to grow things, not pull them out,” he said. But as more and more of them embrace the tactic, he thinks the results will speak for themselves. “My strategy is to identify a few early adopters and let them spread the word and convince their peers of the effectiveness of the new methodology.”
This research was funded by the USDA NIFA Specialty Crops Block Grant Program and the National Institute of Food and Agriculture through the Federal Capacity Funds program. Co-authors of the article include Greg Loeb, professor of entomology, Rekha Bandhari, graduate student, Stephen Hesler, research support specialist, Rosemary Cox, research support specialist, and Tim Martinson, senior extension associate .
For more information, see this Cornell Chronicle story.
American Journal of Oenology and Viticulture
The title of the article
Spatial scrubbing reduces the incidence of leafroll disease and curbs its spread in a Finger Lakes ‘Cabernet Franc’ vineyard
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