Remain vigilant in these uncertain times
14th February 2020
Climate variability has already played a key part this season – from mid-September to the end of the year exceptional rainfall brought the misery of floods and a virtual complete halt to winter wheat drilling for many.
Climate variability has already played a key part this season – from mid-September to the end of the year exceptional rainfall brought the misery of floods and a virtual complete halt to winter wheat drilling for many. And there can be little doubt that it makes it much harder to forecast disease pressure.
“In Hampshire, it started raining on 20th September and, by the end of November, 330mm of rain had fallen,” says AICC agronomist Richard Cromie.
For him, vigilance is now needed throughout the season coupled with what he terms an“appropriate response“ at all timings. “Farming is always at the mercy of the weather, but in the past you had a bit more certainty in the seasons. Usually disease built gradually but now the pressure can fluctuate from timing to timing and you need to react accordingly,” he warns.
Drilling date is as much a factor as the weather, but even later drilled crops have come through mild winters with plenty of biomass in past seasons. It has fuelled septoria and more prevalent eyespot in recent seasons, and typically was treated with an azole + SDHI fungicide combination at T1 to combat early septoria pressure.
This season he expects it might be a little different. Late drilled crops have sat in cold and wet soils, and early biomass is unlikely to match previous seasons. Reduced disease pressure is welcome with yields already likely compromised. “Few crops are likely to break the 10t/ha barrier. Here it might be an opportunity to trim T0 and T1 sprays, and for resilient septoria varieties an azole + CTL might suffice.”
With playing catch-up at T2 unlikely, further savings are possible. He sees T2 mixes being largely protectants, giving more flexibility with chemistry choices. He welcomes new actives coming to market but isn’t expecting significant eradicant activity being needed, which is where the new products fit best.
Instead, he expects an appropriate response to be Ascra (prothioconazole + bixafen + fluopyram) or Aviator (prothioconazole + bixafen) where septoria is the greater threat, or Adexar (epoxiconazole + fluxapyroxad) or Elatus Era (prothioconazole + benzovindiflupyr) where yellow rust is the primary target.
But even if he needs to call upon new fungicide arrivals, it is likely to be mixed with actives such as bixafen, fluopyram and fluxapyroxad. “The best way to protect a product is not to use it, the next best alternative is not to over expose it. I’d prefer to have three or four modes of action at lower doses over robust doses of two,” he says.
Brown rust is also benefitting from climate change. Mr Cromie is seeing it more regularly, although severity does vary. A lack of varietal resistance doesn’t help, nor the slip in SDHI sensitivity, but the big problem is now how rapidly the disease cycles in warm spells. “It cycles faster than any other cereal disease – research has shown a latent period as short as four days. It makes a T3 spray essential for susceptible varieties.”
Yorkshire based AICC agronomist Patrick Stephenson cautions against underestimating septoria pressure in late drilled crops.
Across much of his area, control strategies will also be complicated by the variation in wheat drilling. “If we get favourable weather in the spring by the time we get to T2 there might be little difference from previous seasons. It hasn’t been too cold so far this winter and background septoria will be there.”
He also warns that the loss of chlorothalonil (CTL) will compound climate variability. Its loss strips away a protective layer helping to maintain a protective position throughout the season, with most of the wheat area drilled with mid to high risk varieties; only Extase and Theodore have genuine septoria resilience. Fortunately, he believes most of his customers have secured supply for this season. For those that haven’t an alternative multi-site may not be the answer.
“In AICC trials we don’t see the same consistency of CTL from alternative multi-sites. We think this is a mix compatibility issue but varietal factors could play a part – typically we see stronger responses where varietal rating is low. But more work is needed.”
For northern areas where crops were drilled in good time, he sees a standard four spray programme starting with a CTL based T0. But further south in his area late-drilled crops are likely to race through growth stages making the T1 call more challenging, especially for growers having failed to secure adequate volumes of CTL. As a result, he will consider SDHI T1 rates as an alternative option. His view being that it might be better to lift SDHI rates with some varieties than include an alternative multisite to CTL.
He also welcomes new chemistry and agrees there is likely to be plenty of choice with T2 options this season. “If you need some kick-back then there isn’t much choice but to reach for the most potent options. But if leaves two and three have been kept clean and the risk of transfer to the flag leaf is reduced then we have a range of good protectants. Azole activity is significantly reduced but SDHIs such as bixafen, fluopyram, fluxapyroxad and benzovindiflupyr are still working well.”
Rust wise, slightly cooler conditions in his area mean the threat is mainly the yellow variety. It was more easily found last season, probably helped by mild winter weather and that the time of prime varietal vulnerability is at the juvenile stage. It’s why he feels control emphasis is on the early part of the season. “If you can keep the disease under control between GS29–GS31 then you should keep ahead of it for the rest of the season,” he says.
And he advises growers not to give up on late-drilled crops. He believes there is some hope for a partial recovery and points out that November drilled crops have performed well in YEN trials. “Winter wheat isn’t as elastic as other crops but it can still recover some of the lost ground. The important thing is to make sure that there’s sufficient N in place throughout the growing season. A ‘little and often’ nutrition approach starting with something in the region of 30kg/N/ha in early February will help,” he concludes.