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Don’t forget about mildew, despite cold start to 2021

Winter cereal growers must stay alert to the threat of mildew in susceptible varieties of winter wheat and winter barley, despite the prolonged cold spell at the start of 2021.

The disease was evident in autumn-sown cereals at the backend of last year, but the recent “Beast from the East Two” will have helped suppress it and make it less aggressive.

However, Scottish Agronomy director Eric Anderson says the low temperatures will not have eliminated inoculum and mildew could soon flare up again as the mercury rises this spring.

He explains that 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 adds.

 

Winter wheat

Whilst the area of mildew-susceptible winter wheat variety Leeds has dwindled across Scotland, varieties like Saki, Elicit and Revelation are widely grown and only have a moderate resistance score of 6.

Mr Anderson advises 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.

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 says it may be wise to hold it back until T1 (GS 32 with leaf three fully emerged).

“It gives you about three weeks’ protection, so holding your nerve and applying at T1 may be a better strategy and will see through that critical period,” he explains.

 

Winter barley

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 for mildew), LG Flynn (4) and KWS Cresswell (4).

These susceptible types will again need close monitoring from early- to mid-March and a specific mildewicide included at the T0 timing where disease is active.

With Corbel (fenpropimorph) no longer available, Mr Anderson says 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.

Following the withdrawal of epoxiconazole and being beyond the last date of sale, only on-farm stocks will be available before its 31 October 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.

 

Don’t skimp

As prothioconazole has reasonable protectant activity on mildew, some may believe it is possible to avoid a more costly specific mildewicide in both wheat and barley crops.

However, Mr Anderson stresses that prothioconazole alone will not be sufficient to clear active mildew out of susceptible autumn-sown cereals and needs 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.

“But 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 explains.

Originally published in The Scottish Farmer