13 May 2011

Recent rain showers mean growers need to think carefully about their key T2 fungicide spray options. That’s the advice of ADAS disease expert Jonathan Blake.

“The very dry spring, coming hot on the heels of near ideal conditions for T1 sprays, had prompted some growers and agronomists to consider cost savings, as a repeat of last year’s low disease conditions looked likely,” explains Mr Blake.

“But with wheat worth close to £200/t the potential to push crops for maximum profit was always good, particularly by taking advantage of fungicide products containing new generation SDHI active ingredients, such as Aviator235Xpro (prothioconazole + bixafen).

“As widespread showers pushes Septoria up crops - which are in some cases are significantly shorter than in previous seasons, the case for robust T2 sprays to protect flag leaves is stronger than ever. Yellow rust worries, prompted by early infections in this year’s mainly susceptible varieties, now need viewing in the context of rising Septoria pressure too,” he notes.

“Yellow rust continues to be a problem, but given recent rainfall and the shortness of crops this season, rain splash of Septoria onto the upper leaves is an issue too, making the curative activity of SDHIs very relevant,” he says.

“HGCA Fungicide performance curves show that Aviator235Xpro and Seguris are both good products against both yellow rust and Septoria. There’s really not much to choose between them. But there is a need to watch rates carefully. Full rate Seguris (epoxiconazole + isopyrazam) delivers three-quarter epoxiconazole. That means a three-quarter rate will deliver just over a half rate triazole. I would not be comfortable with that where Septoria tritici is present and active in crops.

“Full rate Aviator235Xpro, by contrast, contains full rate prothioconazole. It is something people need to watch when comparing rates.”

And he reminds growers of the non-fungicidal effects from the new SDHIs in those crops with the best yield potential. “Extended green leaf area duration and yield effects not fully explained by disease control have been largest in crops where there is good yield potential. We would expect the benefits to be less in those that are under the greatest stress,” he adds.