Wednesday, July 24, 2019

Septoria threat to winter wheat despite dry spring

May 1, 2019 by  
Filed under Crops

Early sown winter wheats continue to be at risk of Septoria spreading up the plant – despite the dry spring which has dried up the disease.

Favourable conditions last autumn have helped create some exceptional crops which are building further biomass. But growers mustn’t allow themselves to become distracted by the dry spell, warns Farmacy agronomist Peter Riley.

“Good drilling and establishment conditions helped root development, and with plenty of residual nitrogen for crops to feed on they have boomed. But that has created the ideal canopy to spread Septoria up the plant through greater canopy humidity or leaf contact.”

Regardless of what has happened already, Mr Riley says septoria pressure is ultimately dictated by weather from mid-April to the end of May. A week of wet weather can kick-start disease – and that often happens somewhere between GS32 (T1) and GS39 (T2), as it did in 2012.

Lush canopies mean Mr Riley sees any wheat variety as having a degree of risk. And with plenty of inoculum coming through the winter, he says growers shouldn’t take any chances, even with more resilient varieties.

All wheats will get an azole + SDHI mix at T2 regardless of drilling date and Septoria rating. That is most likely to be Ascra (prothioconazole + bixafen + fluopyram). Librax (metconazole + fluxapyroaxad) and Elatus Era (prothioconazole + benzovindiflupyr) are also options.

It depends on T1 applications and weather subsequently.

“Dry April weather eased T1 application timing for later sown crops, reducing the risk of an extended T1-T2 gap,” says Mr Riley. “But Septoria is a challenging disease and unless it is particularly dry a potent azole + SDHI mix will be employed with CTL.

“For those with large acreages and the risk our maritime climate presents, the temptation to pull T1s forward is understandable. It makes a T1.5 contingency spray more likely as a shot of CTL will be needed to keep Septoria in check.”

That contingency adds another protective layer and opportunity to include a strobilurin or fast moving azole for rusts. It means another pass and higher spray bill but gives more flexibility with product and rate at GS39. CTL might then be unnecessary at the later timing.

Omitting CTL could aid azole and SDHI movement into the plant – useful to improve rust control. Brown rust is an increasing problem in both wheat and barley – with spring and winter barley needing a three spray programme to deal with Ramularia and brown rust in recent years.

Mr Riley is going with Siltra (prothioconazole + bixafen) at GS31, followed by a forward T2 at GS37 to get Bravo (chlorothalonil) in early for Ramularia and then closing with an azole + strob mixture.

He is also seeing yellow rust in later sown susceptible wheat varieties. T1 sprays should keep the yellow species under control although Mr Riley admits that new races and wheat varieties mean it can be unpredictable.

Regardless of any contingency spray, he says every T2 spray should be targeting GS39 (flag leaf fully emerged).

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