Persistent rainfall has created the highest septoria pressure for 12 years and many growers will need to re-consider their T2 spray plans, says Jonathan Blake of ADAS (pictured).

In stark contrast to 2011, yield responses of between 3-4t/ha from fungicides can be achieved this year, he predicts, especially if a multi-site protectant fungicide is added to the flag leaf spray.

“We’re in an extreme situation and there’s good reason to use every tool that’s available,” he says. “Septoria can’t be removed once it’s there, but fungicides can reduce the speed of its development.”

The latent period of the disease means wheat crops always look cleaner than they really are at this time of year, he adds. “The septoria that’s in them isn’t really showing yet. But it will become apparent over the next two weeks, just as most T2 sprays are going on.”

There’s an established relationship between April rainfall and the need for robust treatments, says Mr Blake. “The yield responses to disease control are also linked to the amount of rain that falls in April. That’s why we could see some big gains this season.”

There’s a long history of adding Bravo (chlorothalonil) to triazoles, he says. “We know you get a yield response if you add it at T1 and T2, with the greatest responses coming when it is included at both timings. Higher rates also give more yield.”

Coating new, unprotected leaves as they emerge with a protectant fungicide is sound practice, he believes. “There’s some evidence that chlorothalonil can have a detrimental effect on the rust control offered by a triazole. But there’s no such problem with septoria and you will see a benefit from adding it.”

The same data doesn’t yet exist for the SDHIs, he admits. “We have to go back to 2008, which was the last season the SDHIs were properly tested.”

Adding Bravo to Syngenta’s Seguris in that year improved septoria control, he says. “Where it was included at T1 and T2 it raised yields by 0.8t/ha.”

The slide in triazole performance is another good reason to include a multi-site protectant, says Mr Blake. “We need to find alternative modes of action. This will be an interesting season for the triazoles, as they didn’t show great persistency in 2011. And adding either chlorothalonil or folpet helps to reduce the risk of SDHI resistance developing.”

However, antagonism between Bayer’s Aviator and Bravo has been reported, he warns. “Don’t add chlorothalonil if Aviator is your choice of SDHI.”

Spray windows

Using the right nozzles will help farmers to make the most of spraying opportunities, even in this season’s unpredictable conditions, says Syngenta’s application specialist, Tom Robinson.

The company’s Amistar nozzles have been designed with a small backwards angle, which counteracts the forward speed of the sprayer, to give even spray coverage, he explains.

“There’s also a go-faster version, with a greater angle, for those who like to travel at 16km/hour, rather than 12. There’s no disadvantage to travelling at the faster speeds,” he says.

The reduction in drift with the Amistar nozzle is equivalent to 1 Beaufort Scale unit of wind speed, he says. “In practical terms, that means four extra spray days in May and in June, or an extra day a week.”

The best application advice for Seguris is to use a water volume of 100 litres/ha, a forward speed of 12-17km/hour, Amistar nozzles and a boom height of 50cm above the crop, he says.

“Make use of a boom height indicator and check that your tyre pressures are right, as they can affect the stability of the sprayer.”

To buy Amistar nozzles, call 0800 652 4216 for 24-hour delivery.