Septoria poses huge challenge

Results from the HGCA 2012 fungicide performance trials show how difficult it is to control septoria in an eradicant situation, even when the best chemistry is used at double rate.

Speaking at the HGCA agronomist’s conference in Peterborough, NIAB TAG’s director of crops and agronomy Stuart Knight revealed that although the SDHIs had given superior results to the triazoles in wheat, they were unable to achieve more than 50% control.

“It’s the same message when you look at the results for the last three years. The two leading SDHIs, Aviator Xpro and Adexar, are far better than the two leading triazoles, Proline and Ignite, but neither of them can give more than 50% eradicant control.”

But in a protectant situation, it’s a different story, he noted. “All three of the SDHI fungicides performed very similarly in 2012, including Seguris, giving up to 85% control.”

The triazoles also did well, with both Proline and Ignite giving good results, he added. “They can do a better job at protection and that’s how they should be used.”

Bravo (chlorothalonil) at half dose was very effective. “It was better than the triazoles. And the other multi-site protectant material, folpet, gave useful control, but not at the Bravo level.”

The three-year rankings on protectant activity are similar, he revealed, with Aviator and Adexar coming just ahead of Seguris, followed by a half dose of chlorothalonil, then the two triazoles, Ignite and Proline.

In terms of yield responses, there was nothing to choose between Adexar and Aviator Xpro, added Mr Knight. “Seguris is just behind them, due to its poorer eradication of the disease.”

The top two triazoles can’t be separated on yield either, he said.

Imtrex, the straight SDHI, was included in the trials in 2012 to show how it compared and to give a better understanding of the contribution made by the SDHIs. “It gave very good protectant and eradicant control of septoria, but didn’t match the yield response of Adexar.

“However, it’s important to understand that we are not suggesting that SDHIs are used in this way,” he warned. “They must be mixed with azoles and multi-site protectants and used for their protectant activity, not in an eradicant situation.”

A difficult year for yellow rust made it possible to pull the fungicide products apart, with the value of epoxiconazole being apparent, commented Mr Knight.

“It was a high pressure season. Ignite was better than Proline, although the strobilurin Comet also gave good results.

“The two epoxiconazole-based SDHIs, Adexar and Seguris, were stronger than Aviator on yellow rust, while the straight SDHI Imtrex was behind the triazoles. Brutus, the co-formulation of epoxiconazole and metconazole, was another good performer.”

But over two seasons, the products were all much closer in their activity, he stressed.

On brown rust, the SDHIs were very strong, while epoxiconazole was the best triazole.

A comparison of septoria control with half rates of epoxiconazole and prothioconazole showed just how far they have slipped since their introduction, warned Mr Knight. “In the mid 1990s, these two were giving 85-90% control in a protectant situation. That’s now fallen to 60%.”

At full rate, the decline is less dramatic, but it is still evident. “In contrast, Bravo at half rate has stayed at 70% over the same time.”

However, in an eradicant situation, the triazoles have fallen to 40% control, even at full rate. “This shows how the septoria population has changed to include less sensitive isolates. It’s the reason why triazoles should always be used in mixtures.”

In barley, the strength of prothioconazole was clear in the trials, giving good results against rhynchosporium, ramularia, net blotch and mildew.

“Prothioconazole is the stronger of the two triazoles on rhynchosporium, although both the SDHIs Siltra Xpro and Adexar gave very similar results in an eradicant situation.”

Folpet, the protectant material, gave 50% control. “It has some useful activity, but doesn’t show a strong dose response.”

Over three years, the leading products were Siltra Xpro and Adexar for eradicant control, while Ceriax (Adexar + Comet) joined them for best results in a protectant situation. “And Fandango is another good performer on rhynchosporium.”

On ramularia, Proline proved very strong. “All the SDHIs make a good contribution, but Siltra Xpro has the edge because it contains prothioconazole.”

Net blotch was controlled to a very high level by all of the SDHIs, including Bontima, reported Mr Knight. “And with mildew, spiroxamine and prothioconazole gave good results. Cyflamid had the most activity on established infections.”

No data was gathered on brown rust, as it was a low pressure season, he ended. “But we have a good range of options for controlling brown rust in barley.”

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