Leafroll virus is a harmful illness that shortens the lifespan of vineyards and lowers wine high quality. Glenneis Kriel stories on methods to determine and forestall this illness.
Picture: Prof Piet Goussard
South Africa has a wealthy winemaking historical past, courting again to 1659. Even so, the nation solely has 4 292ha out of 89 384ha which can be 35 years or older, and are recorded within the Outdated Vine Challenge.
One of many causes for that is leafroll virus. No formal statistics can be found on the variety of hectares affected, however Rosa Kruger, founding father of the Outdated Vine Challenge, estimates that at the least 70%, if not 80% of the realm below vineyards in South Africa, is to a point contaminated with leafroll.
She gave extra data on methods to forestall the illness throughout a winery staff growth coaching session held earlier this 12 months in Paarl.
The menace
Leafroll virus impacts plant vigour and ends in uneven and fewer bunches. Yields of contaminated vines are at the least 15% and on common 20% decrease than that of wholesome vines, in line with Kruger.
Together with this, leafroll virus impacts wine high quality, making it troublesome to supply high quality wines and in flip leading to decrease market costs.
Kruger defined that the virus ends in a delay in fruit ripening, uneven fruit maturity, poor sugar accumulation and color growth, particularly in crimson varieties.
“The grape skins flip pinkish as an alternative of its attribute crimson color,” she mentioned.
These are main setbacks, as South African farmers are both chasing excessive volumes to stay financially viable, or specializing in the manufacturing of smaller volumes of higher-quality wine grapes offered at higher costs.
Based on Vinpro statistics launched earlier this 12 months, solely 9% of wine producers are presently producing sustainable incomes. Thirty-eight p.c are farming at a loss, 3% are simply breaking even, and 50% are producing low income.
The discount in yields additionally forces farmers to exchange affected vineyards earlier.
“Vineyards can develop over 50 years previous for those who begin out with wholesome plant materials and vines are saved virus-free. Vineyards, nevertheless, might need to be pulled out after 15 to twenty years when affected by leafroll virus due to the decrease yields,” Kruger mentioned.
Signs
The illness will be latent for a number of seasons earlier than displaying any indicators. In crimson varieties, signs normally begin with a number of uneven reddish spots, and even purple, on leaves at veraison, when the grapes begin to change color.
In the course of the rising season, these spots progressively unfold to cowl most, if not the entire of the leaf, aside from the inexperienced space bordering the principle leaf veins.
The veins have a tendency to show yellow in the direction of the tip of the rising season. Older leaves on the backside of the shoot normally present the primary signs.
Leaves of some crimson cultivars, comparable to Pinot Noir, Cabernet Franc and Merlot, might curl down, however this isn’t the case with varieties like Cabernet Sauvignon, Shiraz and Pinotage. Figuring out leafroll virus in white varieties is tougher, as many don’t present any bodily indicators of illness.
The leaves of contaminated Chardonnay, Cape Riesling and Semillon might flip yellow, whereas these of Chardonnay might also curl down.
Bodily signs on white varieties normally sign extreme infections, in line with Winetech’s ‘Leafroll Management Technique’ truth sheet.
Leafroll virus will be confused with varied different illnesses, comparable to Shiraz illness, Shiraz decline and aster yellows, dietary deficiencies, comparable to potassium, phosphate, manganese or magnesium shortages, in addition to mechanical harm.
Kruger subsequently advises farmers to check their vineyards for the illness in the event that they see indicators of crimson leaves and a decline in yields and wine high quality, so as to determine precisely what they’re coping with.
Begin clear
There isn’t any remedy for the virus, so contaminated vines have to be eliminated as quickly as potential to forestall the illness from spreading. The illness spreads quickly amongst vines, with a median year-on-year enhance of 1,94 occasions within the first few years, in line with Winetech.
Which means that the variety of leafroll-infected grapevines can virtually double annually.
“Vineyards must be monitored repeatedly for the illness. Some farms incentivise their staff to do that by providing a money reward for every leafroll-infected vine they spot,” she mentioned.
Winetech advises farmers to contemplate the removing of a winery when greater than 20% of the vines are contaminated.
The winery could be saved whether it is nonetheless economically viable, however nice care ought to then be taken to forestall the unfold of the virus to different vineyards. The easiest way to forestall the illness is to star toff with virus-free planting materials.
For extra data, e mail [email protected].
