Winter oat growers are being urged to re-assess disease control options this spring, as their 'go-to' fungicide, fenpropimorph, enters its last year of use – while another key active is also under threat.

Unlike south of the Border, much of the Scottish winter oat area has been successfully established, with a similar acreage to 2019 in the ground. Scottish Agronomy’s Greg Dawson said that after a wet but relatively mild winter, the majority of the advisory group’s crops are looking well, depending on drilling date.

“Crops drilled in good time are relatively well established compared to seasons where it is frosty with a cold wind, which tend to upset the oat crop more than the damp weather we’ve had,” he added.

Frost heave can be a major problem and although this remains a threat on sodden soils, once the mercury starts to rise throughout March, attention will soon turn to crop protection programmes.

Mildew is the main threat that's the target of the first sprayer pass at T0 – which is typically in late-March or early April – when the crop reaches late tillering-GS30, potentially including a herbicide if autumn applications were not possible.

That's particularly so on lighter, manganese deficient soils, and on susceptible varieties such as Gerald, which still commands a significant share of the Scottish oat area.

Growers have tended to use the specific mildewicide, fenpropimorph, at T0 to keep the disease at bay until T1 spray time at GS31. Then, product choice is driven by oat septoria and crown rust, with mildewicide added if mildew is still active.

As fenpropimorph sales have now ceased and its use won’t be permitted after the end of October, growers will be forced to re-think how to approach oat disease control next season and beyond. Mr Dawson said growers advised by Scottish Agronomy with stocks on farm have been urged to use up any product containing the active where appropriate this spring.

For those without product and for others with one eye on next season, Scottish Agronomy will be building its winter oat mildew control strategies around cyflufenamid-containing product Cyflamid.

“The question is, when will we deploy it? Cyflufenamid can’t be used in successive sprays for resistance management purposes, so if you choose to use it early in a T0, you won’t be able to use it again at T1,” he explained. The answer will depend on disease pressure as T0 approaches, with high pressure likely to require an early dose of Cyflamid.

Ideally, this would be followed by a prothioconazole-based product, such as Helix, which also contains specific mildewicide, spiroxamine.

Siltra is another option and includes prothioconazole plus SDHI component bixafen, with both active substances having good activity on mildew.

However, if the Cyflamid application has not been used at T0, Mr Dawson said he would revert to his more traditional approach of an azole plus Cyflamid at T1.

The threat to epoxiconazole – which is unlikely to be re-registered due to EU endocrine disruptor regulations – will potentially complicate this T1 azole choice down the line. It is unclear when the active will be withdrawn, but there is a possibility it might not be available for 2021.

In the past and for this season, Mr Dawson will opt for epoxiconazole for oat septoria and crown rust control, but if it becomes unavailable, a straight swap for prothioconazole would be the obvious and preferable choice. “A prothioconazole plus Cyflamid T1 would be a pretty strong T1 option,” he added.

As of early March, diseases such as septoria and yellow rust were being picked up in winter wheat crops and reports were coming in of early mildew infection appearing in winter oats, so conditions are conducive to disease.

Mr Dawson said it would only a matter of time before the mildew flares up in high risk situations, but the issue is being exacerbated by wet ground and sprayers unable to travel in some areas.

Once sprayers can move, he said growers should be aware that T0 tank mixes should not be applied if cold night-time temperatures accompany crops arrival at GS30. “It is always better to err on the side of caution with oats. They can be sensitive to scorch, especially if you are putting any herbicide products in the tank.”