12 April 2002

Taking the fight to take-all at T1 stage

By Andrew Blake

WHEAT growers with potential take-all troubles and still undecided about which fungicide to apply at T1 should remember that only one strobilurin has an effect on the disease.

That reminder comes from IACR-Rothamsted researcher John Jenykn who has been investigating the role of Amistar (azoxystrobin) foliar treatments in reducing take-all infection.

Widespread early drilling and the mild winter are likely to have encouraged the disease, with second wheats on light land most at risk.

The threat, assessed in HGCA/Monsanto trials at ADAS Rosemaund, is more than twice as high as in previous years, says researcher John Spink.

"Seed treatments may help reduce the risk, but given the amount of take-all around we are still likely to see it in crops," says Mr Spink.

Full rate Amistar at the start of stem extension (GS30-31) definitely affects the development of take-all on the plants roots, but quite how is still unclear, says Dr Jenkyn.

HGCA-funded monitoring of Zeneca (now Syngenta) trials in 2000 showed the strob helped lower take-all levels at three of four sites, and significantly so on two of them.

Untangling the yield benefits from such reductions is very hard because of the fungicides control of other diseases, says Dr Jenkyn. "But we have had yield increases.

"The effect is surprisingly consistent bearing in mind it is a foliar spray that is apparently doing something in the soil."

Field trials last year to determine how the chemical might be working, by applying it to the soil, were frustrated by dry weather. But earlier pot experiments suggest there may be a direct effect.

"There is no evidence that any other commercially available strobilurins have an effect [on take-all]," he says.

So for growers with crops at risk, azoxystrobin might be worth considering in preference to anything else, he believes.

Mr Spink agrees. "All other things being equal, and you cant make up your mind, go for Amistar. But there will be plenty of good reasons for choosing something else."

Most of East Yorks JSR Farms 2000ha (5000 acres) of wheat are first crops and so relatively unlikely to succumb to take-all. "We do not drill our second wheats particularly early either," says technical director Philip Huxtable.

"But if any of our managers is concerned about take-all, especially on light soils, we would build in Amistar at T1. In those situations we consider it the product of choice."

Syngentas Chris Rowsell says deciding between the firms two strobs at T1 is relatively straightforward. "We are trying to keep it simple and recommend Acanto for first wheats and Amistar for second crops." &#42

Strob choice for first spray treatments could be worth a fresh look where take-all threatens, according to recent research.

&#8226 Increased risk in second wheats.

&#8226 Azoxystrobin useful at T1.

&#8226 Control mechanism unclear.

&#8226 No other strobs with same effect.