Testing showing resistance issues with botrytis fungicides

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Botrytis resistance testing is identifying resistance issues with commonly used fungicide groups in wine grapes in the King Valley of north-east Victoria.

Muirs Agronomist, Geoff Morrow said they’ve participated in a national fungicide resistance program for many years, taking samples in wine grapes to determine what fungicides are working and which ones are under pressure.

Muirs Agronomist Geoff Morrow said Verpixo fungicide had a good fit in their wine grape spray program with other chemical groups coming under pressure

“For four or five years now, we've actually been taking swabs, a bit like the old COVID swabs, but instead of up the nostril, it's into a bunch of botrytis,” Mr Morrow said. “These samples are sent to researchers at Curtin University, WA to assess resistance levels in the vineyard. We're seeing a little bit of resistance now in Group 9 and 12 chemistries, and to a lesser extent, Group 17. So we take that into account when discussing botrytis fungicide programs."

“In a block you might do ten or a dozen swabs, and each one of those swabs gets assessed. It's quite handy information so you've got something behind you when you might suggest an alternative product.”

Verpixo® Adavelt® Active fungicide was released as a botrytis and powdery mildew product for the wine grape industry last season and was utilised in a number of vineyards in the King Valley.

It is a Group 21 fungicide (which is a new fungicide group) so proved to be an excellent option to rotate with the traditional products coming under pressure with resistance.

“We knew that Verpixo was on the way, and we did get a little bit out last year,” Mr Morrow said. Ï think it’s got a good fit in the botrytis program.”

He said it mixed well with most other products and would be ideal as a rotational partner with other chemical groups.

“There are products we currently use in the program that, hopefully, we can still use those in 10 or 15-years’ time, but we'll need some other groups to help rotate with to keep them going.

While last season wasn’t a high-level year for botrytis, it is a disease that can cause major issues – particularly during the wet seasons.

“Most growers here use a combination of chemicals and cultural means to reduce botrytis, he said. “Botrytis can win if it keeps raining, but it is important that growers implement a program, a mix of cultural and chemical, and see how they can reduce the damage. That’s what growers hope to do in the tougher seasons.”

“With botrytis you can lose yields and quality. Botrytis produces an enzyme that has an adverse effect on wine quality. Wine makers don't like botrytis so there is a lot of incentive for growers to present their fruit with minimal botrytis.”

He said most years they see diseases such as powdery mildew and botrytis and the ability of Verpixo to control both diseases makes it an attractive option.

“The main reason for choosing Verpixo here would be botrytis but its strong activity on powdery as well is an excellent feature.”

Mr Morrow said most of the botryticides were applied at flowering which was a key time for disease.

“It's often where infection starts. You might not see it for a while - it's what we call a latent infection.”

“Another key timing is that sort of peppercorn size, before you really get coverage issues. That’s also where I would be placing Verpixo. You can spray a bit later with Verpixo (EL31) although coverage at this time is more challenging. A common thing we use when assessing whether to use late season botrytis applications is to spray a few rows of Surround out and actually see what is hitting the bunch. If it's not hitting the bunch, there’s not much value in putting out the product.”

Mr Morrow said the King Valley had warm summer days and cool nights making it an ideal setting for viticulture.

Over the years, traditional varieties such as Cabernet, Shiraz, and Merlot have made way for Italian varieties such as Sangiovese, Barbera, and Prosecco as well as traditional white options.

“The tighter bunch varieties are a bit more prone to disease,” Mr Morrow said. “We have plenty of those with Chardonnay, Sauvignon Blanc, Riesling and Pinot Grigio that are pretty susceptible.”

“Traditionally, white varieties are thinner skinned, but the red ones hang out there longer so are at higher risk as well.”