Three-week optimum for fungicide spray intervals

Highlighting the potential yield losses resulting from yellow rust infection, Syngenta’s David Ranner said a third of a tonne was lost for each week after April 1 that the disease was present in an unprotected crop.

Spray intervals were also a key factor in achieving good yellow rust control, with all three agronomists involved in the round table discussion advocating T0 to T1 and T1 to T2 intervals of no more than three weeks.

“If you are specifically investing in yellow rust control, you are better with enhanced T0 and T1 protection with triazoles and ensuring the interval between sprays is not stretched above three weeks.

“That was highlighted last year when growers who did not put on a T0 spray tended to pull their T1 spray that little bit earlier and then, all of a sudden, you were in the middle of April with T1, the middle of May with T2, and whoops that was four weeks and disease came in,” said TAG’s David Parish.

Mr Parish and ProCam’s Dr David Ellerton both agreed there were not many situations where a T0 spray would not be a planned component of a winter wheat fungicide programme.

Significant benefits

A spend of £10-15 per hectare (£5-6/acre) at T0, on something like Cherokee, would bring significant benefits later in the season. “Even in the absence of yellow rust at the T0 timing, a spend of £10/ha would be a good spend. You would get a lot of protection for £10/ha,” said Mr Parish.

Both agronomists identified the end of March/early April as the best timing for T0, but agreed if yellow rust foci established before then, earlier treatment was vital.

“I tend to think in terms of the latter part of March. I don’t like going in earlier than late March but you may have to, and certainly the appearance of any foci of infection would trigger treatment. I don’t think we are going to get them by early March with this weather, but who knows,” said Dr Ellerton.

A late March to mid-April timing is likely to be the most appropriate for T0, said Mr Parish, adding that yellow rust first appeared in Oakley at the end of March last season.

Those growers who had used seed treatments with activity against yellow rust were advised not to be lulled into a false sense of security. While these would have protected crops through the autumn, they were now likely to be running out of steam. “They key is to keep a very close eye on susceptible crops, even if you have used a seed dressing,” said Dr Ellerton.

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