Winter cereal growers are being encouraged to stay alert to the threat of mildew in susceptible varieties of winter wheat and winter barley this year, despite the prolonged cold spell experienced at the beginning of 2021.

Mildew was present in autumn-sown cereals at the backend of 2020, but the recent ‘Beast from the East II’ will have contributed in suppressing it and making it less aggressive.

Despite this, Scottish Agronomy director, Eric Anderson, commented that low temperatures will not have eliminated inoculum and mildew could soon flare up again as the mercury rises this spring – like in this past week.

“Good soil structure, rooting and adequate nutrition minimises plant stress and improves resilience to any disease, including mildew, but this panacea won’t have been achieved in all situations – particularly where saturated soils have limited access to land for nutrient applications such as manganese, crops can be stressed and mildew risk is likely to be higher,” he said.

Winter wheat, whilst the area of mildew-susceptible variety, Leeds, had dwindled across Scotland, varieties like Saki, Elicit and Revelation were widely grown and only have a moderate resistance score against the disease of 6.

“I advise growers to check these varieties in mid-March ahead of a traditional T0 timing and where active pustules are present, a specific mildewicide could be necessary to control the disease,” he explained. “However, growers should consider label restrictions on the most effective mildewicide product, Cyflamid, which does not permit sequential applications in the fungicide programme.”

With the aim for mildew control in wheat to stop infection climbing up from the middle canopy onto final leaf two and flag leaf, Mr Anderson added that it may be wise to hold it back until T1 (GS 32 with leaf three fully emerged).

“This strategy will give you around three weeks’ protection, so holding your nerve and applying at T1 may be a better plan and will see through that critical period,” he explained.

For winter barley, it is a similar story. With several susceptible two and six-row varieties on the AHDB recommended list with scores of 5 or below, including KWS Orwell (rated 3), LG Flynn (4) and KWS Cresswell (4), these will need close monitoring from now and a specific mildewicide will need to be included at the T0 timing where disease is active.

“With Corbel (fenpropimorph) no longer available, Cyflamid will be the best option in these higher-risk situations – despite the extra cost – with the priority in barley to protect tillers and final ears per m2,” he stated.

Following the withdrawal of epoxiconazole and being beyond the last date of sale, only on-farm stocks will be available before its October 31 cut-off date for use. This will result in prothioconazole being used more widely in both winter wheat and winter barley fungicide programmes this year.

Growers are being urged not to skimp on prothioconazole due to it’s reasonable protectant activity on mildew and some may believe it is possible to avoid a more costly specific mildewicide in both wheat and barley crops.

However, Mr Anderson stressed that prothioconazole alone will not be sufficient enough to clear active mildew out of susceptible autumn-sown cereals and growers will require support in the form of Cyflamid.

“You might get away with it in spring barley crops, where most varieties have the ‘mlo’ resistance gene and are rated 8 or 9. However, it’s a different scenario in winter wheat or winter barley where you are battling a higher inoculum loading from the start the fungicide programme and genetic resistance isn’t always so robust,” he concluded.