Rotate fungicides carefully to avoid resistance woes

Rotate fungicides carefully to avoid resistance woes


Farm Online News
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Making sure fungicide modes of action are kept fresh and are not over-used is the key to retaining efficacy against disease.

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Craig White, Bayer, is urging farmers not to put out prophylactic applications of fungicide on crops suffering from disease this year.

Craig White, Bayer, is urging farmers not to put out prophylactic applications of fungicide on crops suffering from disease this year.

IN THE not too distant past farmers were advised of the merits of a prophylactic foliar fungicide application to keep the fungal disease burden down.

However, a Bayer disease specialist has cautioned that growers need to keep their powder dry if they are to retain as many effective modes of action in terms of fungal disease control as possible and said a careful fungicide strategy was required.

"If you use the wrong product early on in the growing you're locked into a particular path for the season and that can mean putting too much reliance on a particular mode of action," Craig White said.

"There are only three real modes of action for foliar fungicides and you have to be very careful about how you deploy them if you are not going to increase the risk of resistance down the track."

Mr White said there were areas with emerging problems with fungicide resistance, to both triazole and succinate dehydrogenase inhibitor (SDHI) based chemistries in places such as the southern WA wheatbelt and South Australia's Yorke Peninsula.

To combat the problem, he said farmers should make sure they were only spraying when it was worth it.

"You want to protect the leaves that make you dollars, that's the flag leaf out to flag minus two, the disease may look bad in the pre growth stage 30 (stem elongation) but it may be a case of holding your fire."

Mr White said the disease load was reasonably heavy in parts of WA this year, with both spot and net forms of net blotch presenting headaches in barley crops.

He said seed treatments could play an important role in protecting plants early in the season and potentially lessening the need for an early foliar spray, while also providing defence against other types of fungal diseases such as smuts and bunts.

"Everyone is different, but the overall advice I have is to know what you are doing, know what disease you are trying to attack and don't waste those precious modes of action."

Where possible he recommended testing for disease, although he acknowledged the dynamic and fast moving nature of fungal disease made that difficult.

Keeping solid fungicide rotations was also important.

"Don't use the same group consecutively and increase the chances of resistance where you can help, be smart with what products you use."

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