After repeated seasons of high downy mildew pressure in winegrape vineyards, and confirmed resistance reported to some widely used fungicides, growers have been eager to access new options and it appears their calls are being answered.
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.
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, 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.
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 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
Consequently, she said the recent arrival of Xivana® Prime fungicide, introducing a new mode of action (Group 49) to grapes, provides control of the disease for up to 21 days.
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,
“Its retreatment interval of between 10 and 21 days adds flexibility. 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.
She said the low use rate of 37.5 to 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.
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.”
Downy mildew damage pictured last season.
“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 also said, “Growers 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.
This article was written by Bayer for Seasons magazine.
Please note: this article contains information of a general nature, and does not take into account your personal objectives, situation or needs. Before acting on any information, you should consider the appropriateness of the information provided, and seek advice on whether it is fit for your circumstances.