5 July 2002

Triazole control doubt

By Andrew Swallow

SUGGESTIONS that triazole control of rhynchosporium is slipping have been overstated, says BASF, in light of disease survey results. However, Scottish advisors making the allegations stand by their warnings.

"The data so far suggests there has been no significant shift in the sensitivity of rhynchosporium to triazoles in Scotland," says BASFs John Peck. "People are getting too hot under the collar about it."

BASFs belief is that none of the apparently disappointing results are due to reduced sensitivity. Inadequate rates and/or poor timing are to blame for the sub-standard performance against what is recognised to be a difficult disease, he maintains.

"In most situations a good triazole plus morpholine at the right time and rate will do the job."

However, SAC Scottish Agronomys Huw Phillips is adamant the survey results highlight hot-spots where triazole rhynchosporium control has tumbled.

"The situation is not as dramatic as early indications suggested but BASF are taking too much comfort in the data they have.

"The results from the hotspot sites are all packed at one end of the sensitivity scale. It is not a cliff edge type of resistance like with mildew and strobilurins but we are definitely on the slippery slope with triazoles and rhynchosporium.

"Perhaps we should call it resilient rather than resistant."

Triazoles will continue to feature in his recommendations, but only for brown rust control in the final spray on barley, he says.

SAC plant pathologist Simon Oxley supports that stance where growers have been growing barley intensively. "We need to keep all fungicides in our armoury as long as possible so to continue to rely on triazoles would be bad news. We suggest growers look at a different mix, such as a strobilurin plus Unix.

"Pyraclostrobin is good, so is Acanto but it is less effective at lower doses. Twist is a good protectant and Amistar is slightly weaker." &#42

Triazoles do still have a place in rhynchosporium control in Scotland, says BASFs Dick Dyason. But others disagree.