As late drilled winter wheat crops pick up with warmer weather, plants could hit early growth stages sooner than anticipated. Experts believe that leaf three emergence, typically at GS32, could be as early as GS31, or even GS30 in some cases.
NIAB technical director Bill Clark says node development may be vastly different from leaf emergence this season, inadvertently resulting in poor T1 fungicide timing. “This season late drilled crops could race through growth stages and the gaps between leaf layers may be particularly short. Internode development is unlikely to be so rapid and growers using this method might conclude leaf three is still to emerge when it is actually out.”
Mr Clark says plant dissection is tricky at the best of times so understands why growers might use nodal stages to assess crop development, which for GS32 is when the second node is 2 cm above the one below it. But regardless of drilling date he would still prefer leaf three emergence checks are made by taking a knife to plants. “Only by taking the plant apart can you truly see where leaf emergence is. It’s important as we don’t have many curative fungicide options so you have to get fungicide timing spot on.”
Where growers can apply a T0 that will give some timing flexibility for T1 sprays. But he warns leaf development could be so rapid that growers simply may not have the window to get around their entire wheat area in time.
Mr Clark also dismisses the idea that Septoria pressure is bound to be low early in the season for late drilled winter wheat, and points out disease can still strike thin crops. “Drilling date clearly impacts disease pressure but I think it would be a mistake to see late drilled crops as not carrying a threat. If you underestimate disease pressure and don’t build in adequate leaf three protection, by the time the flag leaf emerges you could have a respectable Septoria problem,” he notes.
Bayer’s Jennifer Watson agrees and says the additional potency of an SDHI will be welcome in many T1 situations, from both a persistence and curative perspective. “It is where spray gaps get stretched that poses a high risk of disease getting established. Growth stages are likely to be highly variable, and with some crops not having the insurance of a T0 spray some disease could be present on leaf three if it has been out for a while. The curative properties of an SDHI will provide a little clean up.
“Equally Septoria will build if it is wet and humid during April and May, even in late drilled crops. If that leads to a delay in T2 applications the extra persistence of the SDHI at T1 will help here too.”
She acknowledges that azole + CTL has a place at T1 but notes that it needs to be combined with varietal resistance and later drilling, and there is no error margin with timings. “Obviously azole + CTL is a lower cost option than including an SDHI but it is also higher risk. If something goes awry then there is no fallback. Products like Ascra (prothioconazole + bixafen + fluopyram) offer both dose flexibility and broad-spectrum control. At the T1 timing Septoria pressure is unlikely to be severe so rates will be at the lower end of the scale. This isn’t a significant cost uplift over azole + CTL,” she concludes.