Localised yellow rust threat could prompt fungicide switch

Yellow rust in some areas of the country is making for last-minute tweaks to fungicide choices as T1 approaches. But elsewhere low disease is causing few alarms.

Growers in Lincolnshire, parts of Yorkshire and Warwickshire need to watch out for yellow rust on Robigus and Oakley.

Richard Overthrow of TAG says the threat could prompt a change in fungicide choice.

“On varieties which are also susceptible to septoria, you need to decide between prothioconazole, which is stronger on that disease, and epoxiconazole, which is better on rusts.

“It may not be advisable to go for the stronger septoria product this season. It seems that yellow rust can tolerate cold winters.”

It can be difficult to differentiate between yellow and brown rust at this stage, notes Bill Clark, director of Broom’s Barn. “It could be both.”

But either way, a triazole at an appropriate dose will be effective. “Add chlorothalonil to it, but don’t use the latter on its own,” he says. “It can make rust worse.”

Mr Clark also advises growers to spray a bit earlier this year. “Backwards crops produce fewer leaves, so leaf 3 is likely to be coming out at GS31. This year is the exception to the normal advice of waiting until GS32.”

In Hampshire, AICC member Steve Cook is relaxed. “Only septoria is present, rusts are notably absent and crops are still quite a long way back.”

He will be using protectant sprays at T1, based on either 0.4 litres/ha of Proline or 0.5 litres/ha of Opus, both with chlorothalonil. “Some will need a mildewicide adding, but not all.”

Stem-base browning hasn’t been seen, adds Mr Cook. “We’re going to have fewer leaves to keep clean this year. It’s a case of so many fungicide choices, so little disease at this stage.”

Norfolk-based Andrew Melton of Frontier is another without serious concerns. “Septoria is there, as always, and we’re keeping an eye on Rogibus and Alchemy for rusts. But I don’t expect T1s to be going on until the last week of April.”

Steve Baldock of Prime Agriculture in the eastern counties reports the same picture, but will be taking action against eyespot. “Around 60% of the wheat we have in the ground is susceptible to eyespot and a great deal of min-till is used.”

For this reason, Tracker plus chlorothalonil is his preference at T1. “On the remainder, which comprises varieties such as Humber and Claire that don’t get eyespot, we’ll be using Ennobe.”

Ennobe is well priced and will take care of the twin threats of septoria and rusts, he adds.

Chris Rigley of Yorkshire Arable Marketing also favours an epoxiconazole/prochloraz mix, having used the combination for the last five years. “I’ll nudge rates up where a T0 hasn’t been used, but there’s very little disease around.”

Generating root mass remains a priority for him, so phosphite and trace elements will be part of his strategy. “On second wheats, I might switch to prothioconazole for the T1 spray.”

All agree that growers who opted not to use a T0 spray must be timely with the T1 application.

Chemistry

  • Proline – prothioconazole
  • Opus – epoxiconazole
  • Bravo – chlorothalonil
  • Tracker – boscalid+epoxiconazole
  • Ennobe – epoxiconazole+prochloraz

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