Winter wheat growers are being urged to do everything possible to ensure T2 flag leaf fungicides are applied on time this season.
This follows concerns that disease could have already established in lower parts of crop canopies – due to reduced use of T0 fungicides earlier, coupled with concerns that some T1 fungicides will have been applied too late.
“Certainly, fewer crops than normal received T0 fungicides against early disease pressure,” says Syngenta Senior Field Technical Manager, Iain Hamilton. “Often, this was because conditions were simply too wet to spray.
“When the bad weather did finally break, the sudden spike in temperature in April resulted in rapid crop growth – so leaf three, which the T1 fungicide is designed to protect, emerged unexpectedly quickly. If T1 fungicides went on late, leaf three could have been left exposed to infection for several days.”
Already, from crop inspections, Mr Hamilton says Septoria tritici is rampant in the west of the country, while the return of higher temperatures will see yellow rust cycle faster in eastern and western regions, even though infections were starting from low levels.
“If people were late with T1 sprays, the temptation is to also delay the T2 spray, because the interval between T1 and T2 can seem short. That’s the worst thing you can do, especially if the T1 wasn’t reinforced in response to being applied late or where a T0 was omitted.
“In general, the optimum is to apply the T2 fungicide as soon as the flag leaf is fully emerged, at GS39. Too late, and disease could already be gaining a hold on the unprotected leaf surface. Too early, and the base of the leaf won’t have emerged fully, so you’ll be leaving this part of it unsprayed.”
Lincolnshire-based independent agronomist, Ruth East, is also concerned that a shortened T1 to T2 interval – caused by crops racing through growth stages to catch up after the late start in her area – might lull growers into being late at T2.
Septoria tritici is the main driver to get spray timings right, she says. However, humidity caused by low cloud and sea frets also makes yellow rust a problem in her area, she notes. In response to both diseases, she tried new SDHI-based fungicide, Elatus Era in the T2 slot last year.
“The problem with yellow rust,” says Ms East, “is that some varieties have such low resistance that you can’t afford to leave it for more than two weeks. Yellow rust pressure has been low, but once it gets going it becomes more difficult to kill.
“You can’t take your foot off the throttle; otherwise low disease years tend to end up as high ones. I used Elatus Era on varieties prone to yellow rust at T2 last season, and that’s where I’ll be using it again.”
According to Iain Hamilton, trials on Elatus Era show it has matched or even beaten alternative SDHI-based treatments against Septoria tritici, and has set a new benchmark for Rust activity. “The other major benefit has been its persistence. It produced long-lasting retention of green leaf area,” he adds.