New weapons in the fight against grapevine leafroll disease

Research, genetic selection, machine learning and drones are being investigated as possible means to strengthen the fight against grapevine leafroll disease. Glenneis Kriel spoke to the experts.

Despite huge awareness campaigns, many South African grape farmers are still not taking grapevine leafroll disease, caused by a virus, seriously enough. Vinpro consultant François Viljoen said during a leafroll information session held at Vergelegen wine estate near Somerset West, Western Cape, that he simply could not understand why: "By now it is general knowledge that leafroll virus negatively affects farm income, as it results in lower production volumes and grape quality.

"It also significantly reduces the longevity of the vineyards, meaning vineyards should be replaced over shorter periods. You will be lucky if a leafroll-infected vine lasts longer than 15 years." Prof Gerhard Pietersen, a plant virologist at Patho Solutions, said the virus is severely underestimated in the table grape industry: "We tested 145 vines from 25 vineyards in five major table grape-producing regions between 2017 and 2020. The virus was found in every vineyard we sampled, and over 110 of the samples tested positive."

Despite this, he did not know of any table grape farmer who followed a leafroll management strategy like the one used in the wine grape industry. "Farmers in the table grape industry seem to be less aware of the negative impact of leafroll virus on production. This is probably because the virus takes a few years to manifest symptoms on vigorously growing vines, and table grape vineyards are replaced over a much shorter time than wine grape vineyards, in response to changing market trends and genetic improvements," he said.

Nevertheless, the virus is taking a toll on table grape income. Pietersen pointed out that Patho had identified leafroll virus as the cause of poor colouration on Crimson seedless grapes in a study done between 2019 and 2021. Research on wine grapes had also revealed that leafroll led to uneven ripening and berry sizes.