Better returns this year from strob sprays
Growers are likely to achieve better returns from using strobilurin fungicides this season in winter wheat than in any of the previous three years, says Syngenta‘s Matt Pickard.
Yield responses from the addition of strobilurins to a base triazole + chlorothalonil fungicide programme have consistently averaged 0.4t/ha over that period and there is no evidence to suggest this season will be any different, he says.
But, with grain prices higher this season, and a 20% drop in strobilurin prices over the past four years – equivalent to a £3/ha cut in the cost of a half dose – returns will increase, he says. “When grain prices were around £60-65/t and growers were spending £15/ha on strobs, they were more or less getting £25/ha back for that spend.
“Spot futures are around £85-90/t, and there are contracts out there for those prices, so growers should be getting about £30/ha back for a £12/ha spend.”
That is assuming the average 0.4t/ha yield increase, but Mr Pickard suggests that targeting applications correctly can help growers beat the average.
Improve rust control
For example, with rust rife this spring, strobilurin fungicides can improve rust control over triazole programmes, his colleague Jeremy Godwin says.
In trials on Robigus last season the addition of Amistar Opti (azoxystrobin + chlorothalonil) to an epoxiconazole-based programme significantly increased yield by 0.4t/ha, while an improvement of about 3-4% in control of brown rust on Alchemy was achieved in another trial.
The key to strobilurins’ extra yield from rust control comes from their longer persistence. But strobs also give some curative activity, Dr Godwin says. “It is dependent on dose, but at 0.8-1 litre/ha Amistar (azoxystrobin) gives around four days’ curative activity against brown and yellow rust.”
Variety is a second important consideration when targeting applications, Syngenta suggests. Strip trials in the past three seasons have clearly shown differences between varieties in how they respond to strobilurins, Dr Godwin says.
Responses
The trials compare a triazole/chlorothalonil programme with the same programme with a half dose of strobilurin added at T2 and a third dose at T3. High responders include varieties such as Malacca, Alchemy and Gladiator, while lower responses came from Hereward, Zebedee and Einstein.
“A low response doesn’t necessarily mean using a strobilurin is not worthwhile,” Mr Pickard stresses. “For example, there could be quality issues that need to be considered.”
One of the reasons behind the differential response could be due to green leaf retention. Visual images of the plots showed clear differences between the amount of green leaf retained in the strob plots compared with the triazole plots for some high responders, such as Malacca, while both strob and triazole plots had about the same green leaf in a low responder Zebedee, Dr Godwin says. “You maximise yield by preventing or alleviating things that induce green leaf loss, such as disease or stress. But if a variety stays green it is hard to keep it greener for longer with a strobilurin.”