Ignore short intervals to spray wheat flag leaf fungicides at optimum timing

Flag leaf sprays should not be delayed past full flag leaf emergence, even if T1 sprays have only just been applied, say agronomists. Applications should focus primarily on controlling septoria, they add.

A huge amount of T1s – maybe 95% – had only been applied in the last week, David Parish of The Arable Group, said on Tuesday [5 May]. “And there are still a few to go on, although, hopefully, most growers should be up to speed in the next couple of days.”

But flag leaves were already just starting to show in some crops, he noted. “They’re likely to be fully emerged by the middle of next week.”

That would leave growers with a potentially tricky decision on whether to spray immediately, he said. “But in a funny sort of way, growers need to ignore the shortness of the interval between T1 and T2.

“It is not significant in the sense that with a late T1 there is a chance that disease will be established on the top half of leaf three, and that will be directly in contact with the flag leaf as it emerges, so it is important to get the flag leaf timing right.”

Bill Clark of Broom’s Barn advised growers to inspect crops carefully, especially the tips of leaf three, as the flag leaf emerged for just that reason. “If you can see septoria on the tips, it shows the T1 sprays were not on in good enough time and adds to the urgency for flag leaf sprays.”

Those crops would need spraying sooner rather than later, he said. “If you can’t see disease on the tips, then wait for the flag leaf to be fully out and then go.”

Agrovista‘s Mark Hemmant reiterated the need for growers to not wait for ear emergence before spraying again, even if they had only just applied a T1. “You need to protect the flag leaf. Once it is out it would be crazy not to spray it.”

He also warned against cutting doses. “There might be a temptation to cut dose if you’ve only just put a T1 on. But you may be chasing disease on leaf three and will need a robust dose of eradicant activity.”

Sean Sparling of Lincolnshire was advising growers to use a three-quarter to four-fifths label dose of either prothionazole or epoxiconazole at flag leaf. “The key for the whole thing is getting the right triazole dose for septoria control.”

Rust should not be forgotten when choosing products, Mr Clark said. “It is still there, albeit not going wild. But with a week of high temperatures it doesn’t take long for it to take off.”

Mr Hemmant suggested that while it was a lower disease year for rust than last year, the fact that there was any coming out of winter still presented some risk. “It means you cannot ignore strobilurins.”

Mr Parish also advocated using a strobilurin, but his first addition to the triazole-base would be chlorothalonil. “I know there were some issues with it impeding triazole activity on rust last year, but we’re not dealing with that problem this year. Additional septoria protection is going to be important. We must get septoria control right this year.”

Flag leaf advice

  • Watch out for septoria infections on leaf-three tips
  • Don’t delay flag sprays because of short intervals from T1
  • Septoria key disease
  • Don’t discount rusts