Cold weather unlikely to stop yellow wheat rust outbreak

 

 

Low temperatures are unlikely to prevent early outbreaks of yellow rust occurring this spring, making spray timing and intervals extremely important.

 

While sporulation stops at temperatures below 0C, yellow rust mycelium can survive in the leaf until temperatures rise again, said Syngenta's fungicides technical manager Dave Ranner.

 

January and February temperatures do determine rust risk and appearance date, but although the brown rust risk is reduced by cold winter temperatures, yellow rust is not so easily deterred, said Ranner.

 

There are insufficient frost to reduce the yellow rust threat in the eastern counties and the Midlands, he said.

 

Nickerson's Paul Fenwick said yellow rust manages to survive the harsh Canadian winters.

 

Crops under a blanket of snow are insulated. Any yellow rust lesions are held in a state of suspended animation - if conditions remain cold for another few months there may be a delayed onset of the disease but the threat will remain, said Fenwick.

 

About 60% of wheat varieties in the ground this year are susceptible to yellow rust, while 85% of certified seed sown is susceptible to some form of rust, said ProCam's technical director David Ellerton.

 

“Fortunately, we've had the variety information in advance," he said. "We also have the fungicide armoury to deal with the rust diseases and can knock them on the head."

 

Most varieties had one of yellow or brown rust in them last season, he added.

 

Brown rust came in later on and it is likely to do the same in 2010. But yellow rust is different, as it appears in crops before the cold spell begins and will simply remain, according to Ellerton.

 

David Parish of The Arable Group believes wheat crops which had enough moisture at drilling time and grew away rapidly are more at risk. He added that the implications of snow cover are not fully understood.

 

"If we get a degree of leaf death, that could help remove some yellow rust infection. But it will be important to get some protection on at T0 and T1 this year."

 

That means keeping the spray interval to three weeks, he said. The normal T0 timing is late March, but if there are obvious foci of yellow rust appearing in fields, this may have to brought forward, said Parish.

 

Ellerton said timing and spray intervals are crucial with all diseases, and curative activity is needed with the rusts.

 

Getting the T0 right for rust is even more important where a prothioconazole programme is planned for T1 and T2, he adds.