Fine-tune flag leaf sprays

Wheat growers should be prepared to make changes to their T2 applications if spray schedules have been disrupted by the cold, wet spring.

With septoria levels already higher than expected and yellow rust starting to appear in susceptible varieties, it is possible to get things back on track with a review of fungicide and PGR inputs ahead of the all-important flag leaf timing, believes Chris Bean, technical director of Zantra.

“As a result of the cold, wet spring and subsequent delays, there are plenty of crops which didn’t get a T0 and only received their T1 spray in the first week of May, when sprayers could finally travel,” he explains.

“There are others which had an early T1, due to the heightened disease threat, and are now at risk of having a longer gap between T1 and T2.”

Mr Bean notes that next two to three weeks will be very telling, as there have already been plenty of rain splash events and they look likely to continue throughout May.

“With temperatures starting to rise, crops are now moving rapidly through their growth stages,” he reports. “Unless it dries up completely there is potential for disease levels to explode.

“Another threat is that weaker strawed and leggy varieties are at risk of lodging if the T0 was omitted, as they missed their first PGR.”

Given the delays and saturated ground conditions, he warns that there’s unlikely to be time to apply a T1.5 or holding spray this year, so the emphasis should be on increasing fungicide rates where necessary and strengthening PGR programmes as the T2 application approaches.

“These changes may mean a higher spend at T2, anything from £5 to £15/ha more,” he acknowledges. “But the lessons that we learned in 2012, which was similar in some ways to this year, underlined the importance of tight spray intervals and robust fungicide rates in such conditions.”

Growers planning an SDHI/triazole/chlorothalonil mix at T2 should consider increasing the triazole rate, he suggests. “Where you were intending to use 0.5l of triazole, it would be sensible to increase that to 0.75l.

“Chlorothalonil should be included as a matter of course at T2, except where you have decided on Aviator as your SDHI component.”

In addition, varieties which are prone to lodging may need an ethephon-based PGR included at the flag leaf timing, he adds.

“We know that the likes of Siskin, Motown, Zulu, Barrel and Basset respond well to PGRs and will need some rear-guard action if the T0 was missed. Even where it was done, low temperatures may have reduced the effectiveness of some PGRs.”

Mr Bean recommends that growers ask themselves some questions about their spraying progress to date before finalising their T2 plans with their agronomist.

“Did you manage to do a T0? Was the T1 application well-timed? Did sprays go on in good conditions? Did it rain heavily soon after application? All of these will have a bearing on your T2 strategy and the products and rates you will need.”

His final point is about spray timing at T2. “Wait until the flag leaf is fully emerged. The SDHIs need the full flag leaf to be present for best results.”