HIGH yield potential but soaring disease pressure after the wet spring will make it essential to keep wheat crops disease-free towards the end of this season, a leading technical advisor is urging.
According to Chris Rowsell, Syngenta technical manager, with up to 50% more rain falling in April than the 30-year average, yield prospects look much better than last season. But pressure from wet weather disease has been building, he stresses. So crops must be kept clean if yield potential is to be met.
"With the top leaf, or flag leaf, contributing up to 45% to yield in wheat, and ears contributing up to 25%, both will be important to protect.
"Every day that healthy, green leaf area is maintained during grain-filling can add 0.15-0.2 t/ha to yield. Importantly, strobilurin fungicides such as Amistar are well known for maintaining green area and boosting yield at this time."
Specifically this season, Mr Rowsell says a move away from strobilurin use at the earlier T1 timing could play right into growers' hands - since the two strobilurin sprays permitted per crop can now be targeted to protect both flag leaves at T2 and ears at T3.
"This could be just what growers need. Trial results last season showed an extra 0.26 t/ha yield following Amistar use at T2 and T3, compared with strobilurin use at T1 and T2. That was worth an extra £21/ha margin over fungicide costs. "Also, that was in a very dry season when crop potential was lower. In a year like this, from a risk management viewpoint, applying an ear spray is more important than ever."
While Mr Rowsell suggests a tank mix of Amistar + triazole for ear sprays, he says concerns about fungicide resistance mean it is important to add a third fungicide mode of action, in the form of Bravo, when treating flag leaves at T2.
"This helps control resistant Septoria tritici strains," he stresses. "Alternatively, the new product Amistar Opti contains Amistar and Bravo combined. Mixing it with a triazole can be more cost-effective than mixing the three different products together.
"Even if you can't see disease yet, leaves will almost certainly be infected. It's only a matter of time before symptoms appear."
