Global Agriculture

Grapegrowers look to new option for downy mildew

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18 August 2023, AU: After repeated seasons of high downy mildew pressure in winegrape vineyards and confirmed resistance reported to some widely used fungicides, growers have been eager for new options and it appears their calls are being answered.

Mandy Mader from Vine Scout consultancy inspects a grape crop

Image: SA viticulturist Mandy Mader, who operates the Vine Scout consultancy in the Barossa Valley, says reduced effectiveness of existing downy mildew fungicides has become a big concern for growers and they have been keen to expand their options and also target applications at different times of the season to suit various vine phenological stages.

Independent South Australian viticulturist Mandy Mader, of Barossa Valley-based consultancy, Vine Scout, said La Nina weather conditions caused higher disease levels last season and once again this highlighted reduced efficacy from metalaxyl fungicide (registered and permitted for use in grapes in formulation or mixture with copper or mancozeb), as it has from strobilurin chemistry in previous years.

Mandy, who previously worked with several high profile wine companies, provides extensive technical and monitoring services to small and medium winegrape operations throughout the Barossa Valley, Eden Valley, Adelaide Hills, Clare Valley, McLaren Vale and Riverland regions in South Australia.

She said downy mildew can cause crop loss prior to flowering and leaf loss near the end of the season, which impedes fruit ripening, size and sugar content. In addition, time and cost pressures increase for growers and operations become more labour-intensive, as they have to adopt cultural control methods including thinning and leaf plucking, and, for organic growers, keeping weeds low under vines.

Downy mildew damage in grapes

Image: Downy mildew damage pictured last season.

Mandy said copper as well as metalaxyl co-formulations and strobilurin fungicides had predominantly been used against the disease and their reduced effectiveness had been due to overuse, a lack of fungicide rotation and some hesitancy with new technologies.

Organic vineyards also don’t have the option of chemical fungicides due to controls on copper and sulphur use.

Mandy said the reduced effectiveness of existing fungicides had become a big concern for growers and they had been keen to expand their options and also target applications at different times of the season to suit various vine phenological stages.

Consequently, she said the recent arrival of Xivana® Prime fungicide, introducing a new mode of action (Group 49) to grapes with the active ingredient, fluoxapiprolin, providing control of the disease for up to 21 days from applications as late as E-L31 or 7 mm pea size (pre-bunch closure), had provided a shot-in-the-arm for the industry and grower confidence.

Developed by Bayer Crop Science, Xivana Prime is registered for use in both wine and table grapes and acts on all stages of the downy mildew lifecycle, providing a strong tool in protective programs. In line with Croplife recomendations, Xivana Prime should always be used in conjunction with a registered protectant fungicide and applied prior to disease infection.

In previous widespread testing of grapevines for downy mildew resistance to fungicides, it also showed no resistance in any samples tested from across all regions.

“It’s another mode of action, so it will be great for growers to swap up their chemical groups and it will take the pressure off existing fungicides,” said Mandy, who also was awarded viticulturist of the year for the Barossa region in 2022.

“Its retreatment interval of between 10 and 21 days adds flexibility and its use window up to E-L31 or 7 mm berry stage also provides extra time before application. It allows growers to do other jobs, it saves time and money, and it ticks a lot of boxes including reduced passes in the vineyard, soil compaction, labour and, on a sustainability front, energy.

“The export application window with some of the other systemic fungicides, including Revus® and metalaxyl con-formulations, is only up to E-L 25 or 80 per cent cap fall.”

She said the low use rate of 37.5-50 mL per 100 L was user friendly compared with applications of up to 250 g per 100 L with some other fungicides, and was another cost saving as well as benefit for product handling and packaging.

Experts from Bayer, Vine Scout consultancy and Elders inspect a grape crop

Image: Steve Fiebiger, Elders Roseworthy SA, independent viticulturist Mandy Mader and Darren Alexander, Bayer Horticulture Territory Business Manager in SA, pictured identifying downy mildew damage in vineyards last season and discussing the effectiveness of new mode of action fungicide, Xivana Prime.

Another advantage of Xivana Prime, when used as directed, is its safety profile with beneficial insect populations, which Mandy said needed to be protected to help maintain ecological balance in vineyards and assist control of unwanted pests.

However, she said its main strength was the rotation flexibility it now provided for growers’ fungicide programs.

“Growers don’t have to use back-to-back metalaxyl co-formulations or mixtures. They can go with Xivana Prime after the first application of metalaxyl and they can apply it before rainfall or a downy mildew event occurs and have confidence that it will prevent development of oil spots.”

“Under the high disease pressure last season, we didn’t see any oil spots form where growers had applied it prior to a downy mildew event.

“It’s got a place in everyone’s program for downy mildew and it’s brought massive confidence to our grower base.”

Mandy said the best approach for growers in high pressure years was continued monitoring and rotation of fungicides, while the timing and coverage achieved with applications also was critical and Xivana Prime, in conjunction with a copper protectant spray, fitted perfectly between E-L 25/26 through to E-L 31.

“There is a lack of options to use at this critical timing outside of copper, so it’s providing another systemic fungicide that can be used.”

“Growers also apply light brown apple moth protectants at this time of year, and in mixtures with Xivana Prime, and also where magnesium and zinc has been added, compatibility has been excellent.

“Xivana Prime is also translaminar, so to increase coverage across leaf surfaces and get the best effectiveness from the fungicide, it’s very important to apply the adjuvant with it. Furthermore, applying an additional mode of action protectant fungicide in conjunction with Xivana, like copper, is recommended at all times to help maintain a strong resistance management program,” she said. 

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