Charts show strength against diseases

1 March 2002

Pyraclostrobin pulls ahead

The arrival of two new strobilurins this spring is particularly timely. Along with older products they increase growers chances of success in what promises to be a high disease season. This special focus, edited by Andrew Blake, aims to assist critical input decisions against the background of low grain prices and the ever-present threat of resistance. Andrew Swallow begins with a look at the novel p-strobs

CURATIVE and systemic activity are the key attributes of the two new strobilurins – pyraclostrobin from BASF and picoxystrobin from Syngenta – that set them apart from their predecessors, say experts.

Pyraclostrobins strength is its curative activity, notably on septoria. ADAS plant pathologist Bill Clark says that exceeds even the best triazole, Opus (epoxiconazole), and it is more persistent. "It is the first strobilurin with serious eradicant activity."

But it should still be mixed with a triazole to cut risk of resistance developing, he stresses. "It will be available as a straight but should never be used alone."

That eradicant activity comes on top of physiological processes that have the potential to boost yield in the absence of disease, a fact reflected on the label of pyraclostrobin products, a first for any fungicide.

Usage of nitrogen is increased and ethylene production in the plant suppressed, delaying senescence. "More nitrate uptake leads to bigger plants which results in increased carbon dioxide assimilation, hence yield," explains Mr Clark.

Picoxystrobins edge over older strobilurins is its systemicity and activity on barley diseases.

"It is truly systemic and moves in the vapour phase." Despite star-ratings on wheat diseases only on par with current strobilurins (see tables) that means it could have a place at T1," he says.

"It runs down in the moisture on a leaf into the axils where it gets taken up by the emerging leaf. This is very useful especially if you are going slightly early, have variable growth stages, or are not quite sure what the growth stage is. It makes the timing to protect the emerging leaf three a little less critical."

However, it is not the product for the flag leaf spray on wheat. Older strobilurin and triazole mixtures offer comparable control at a probable price advantage and pyraclostrobin has a clear edge, he says.

"But on barley it is a different story because picoxystrobin is fantastic. It is better than Amistar on net blotch and rhynchosporium and Amistar itself set new standards."

But curative activity on rhynchosporium is limited to a couple of days, and control once disease is established remains a problem – hence the two-star rating.

&#8226 Pyraclostrobin best on septoria.

&#8226 Picoxystrobin edge in barley.

&#8226 Both need partners.

&#8226 Timing still critical.

Charts show strength against diseases

CONTROL curves for the new strobilurins against the key diseases of winter wheat and barley tell the story on how they should be used, says ProCam technical director David Ellerton.

"Both are very strong products and both are likely to feature in programmes this spring.

"Pyraclostrobin has outstanding curative activity on septoria tritici and is better than anything I have seen on rusts. Picoxystrobin is the stronger barley product."

On wheat, as a rule of thumb, Dr Ellerton suggests growers use a half dose of strobilurin at T1 and a three-quarter-rate at flag-leaf. Whether it is worth spending the extra on the new products depends on the disease susceptibility of the variety, he believes.

Consort and Riband are prime candidates for pyraclostrobin but Malacca, with better disease resistance and lower response to fungicide treatment, may only merit one application.

Whether that goes on at T1 or T2 will depend on the spray regime. If a good dose of pyraclostrobin is applied at GS32-33, a late T1 timing, then applying the second strobilurin as Amistar (azoxystrobin), probably mixed with Folicur (tebuconazole), on the ear at GS49-55 is a possibility, saving a pass.

"But I prefer to stick to standard timings. The problem with delaying the flag leaf spray until the ear is out is if the weather then causes a further delay you are in trouble. You must remember it is the flag leaf that produces most of the yield."

Despite its strong curative activity against septoria, Dr Ellerton warns growers not to drop too low with triazole doses.

"You need enough triazole to do the job – 0.2 litres/ha is stretching it to the absolute limit. I think 0.3-0.5 litres/ha is safer."

Growers going below those triazole rates are taking an unreasonable risk with resistance, he believes. Mildew may be the only disease to have overcome strobilurins so far, but irresponsible use could see rust, or worse still, septoria overcome strobilurin controls.

"We have to protect what we are using now," says Dr Ellerton. &#42

Disease YR BR ST SN

Azoxystrobin *** *** *** ***

Picoxystrobin ** *** *** ***

Pyraclostrobin *** *** **** ****

Trifloxystrobin * ** *** ***

YR = yellow rust; BR = brown rust; ST = septoria tritici; SN = septoria nodorum.

Disease Mw BR Ry NB

Azoxystrobin *** **** * ***

Picoxystrobin *** **** ** ****

Pyraclostrobin *** **** ** ***

Trifloxystrobin *** *** ** ***

Mw = mildew; BR = brown rust; Ry = rhynchosporium; NB = net blotch. Source: ADAS.

Picoxystrobin, as Acanto, and pyraclostrobin sold straight as Comet, Tucana and Vivid, and with epoxiconazole as Opera, expand the disease control armoury.

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