Barley growers have a fresh weapon this season in the battle against rhynchosporium, a significant disease steadily overcoming older fungicides.
Kayak, a newly-launched liquid, more rainfast formulation of cyprodinil, as in wettable granule Unix, offers 25% better control than that product. And, with no new active ingredients on the immediate horizon, it can slow triazole resistance, says Syngenta.
“Barley growers often complain about the crop’s inconsistency,” says the firm’s Matt Pickard. The latest product should help reduce that variability just when better prices are tempting many who abandoned the crop to grow it again, he believes.
Much more is becoming known about rhynchosporium, not least that seed can be a potent source of infection and that resistance ratings in winter barley may be unreliable, according to SAC pathologist Simon Oxley.
But his main concern is that the effectiveness of some triazole fungicides, key defences against rhynchosporium, has declined.
Previously valuable weapons, like triadimenol, propiconazole and flusilazole, have fallen by the wayside leaving growers increasingly dependent on epoxiconazole and “current star” prothioconazole, says Dr Oxley.
“The question is can we stop history repeating itself and stop the slide that seems to happen with these fungicides?”
Besides also offering net blotch and mildew control and protecting against eyespot, cyprodinil can help, he believes. “Cyprodinil offers a different mode of action to triazole and strobilurin fungicides making it a useful mixture partner.”
Kayak is not recommended for use alone, and the way it works remains unknown, notes Syngenta’s Dave Ranner. “But there’s good evidence that mixtures or alterations [in spray programmes] can slow the shift in triazole sensitivity.”
Two years of glasshouse experiments on field samples suggest there has already been a slight shift in rhynchosporium’s sensitivity to prothioconazole, he claims. “It’s not as bad as with the older triazoles, but we must keep an eye on it.”
Tests on one of the least sensitive rhyncho strains showed Kayak giving nearly 90% control while the best from a triazole was only 60%, says Mr Ranner.
In developing the liquid the target was 25% better activity against the disease, he explains. “We found Kayak not only achieved the increase in control, but did so using less active ingredient.”
Achieving a liquid version of cyprodinil was not easy, says Syngenta’s Dave Bartlett.
It took the company six years to arrive at the patented oleic acid formulation that allows the cyprodinil to penetrate the plant much faster than as a wettable granule. “There’s a big difference in uptake [compared with Unix],” he says.
Laboratory tests show that after only three days 80% of the Kayak applied to a leaf gets taken up internally. But even after a week barely 20% of sprayed Unix is absorbed.
Tests comparing it against Unix on samples inoculated with rhynchosporium two days after treatment showed its preventative activity was much the same. But results on samples inoculated two days before application confirmed its curative action was much better. “Proline plus Kayak will be a very strong option in barley.”
Independent work suggests Kayak plus azoxystrobin + chlorothalonil can deliver better yields than fluoxastrobin + prothioconazole, he adds.
Noting that the price of the latter two are outside the firm’s control, Mr Pickard says: “Mixtures with Amistar Opti will be competitive with Fandango.”
PROGRAMMED MIXES URGED
Seed treatments’ impact on rhynchosporium is under investigation. But for now winter crops are “bombarded” by the disease from the outset, and protection is easier than eradication, says Dr Oxley.
“You need to start spraying early in spring to give it a headache. But don’t forget other diseases like net blotch and mildew.” The key timing, GS31, is earlier than wheat’s GS39.
While prothioconazole is highly effective he is worried that it may be over-used. “If growers start using just Proline followed by Proline we could end up losing it.”
Instead he advocates a programme of mixtures, for example:
GS25-30 -cyprodinil + spiroxamine
GS31 -prothioconazole + strobilurin or cyprodinil
GS49-59 – prothioconazole + chlorothalonil