Long-term fungicide trials highlight need to support azoles

Date:03-22-2013

SDHI mixtures all showed similar levels of protectant activity, but there were differences between individual products in terms of eradicant activity, an HGCA fungicide performance breakfast meeting for growers in Newmarket heard.

Commenting on the protectant activity against septoria tritici of the fungicides involved in the HGCA trials, NIAB director of crops and agronomy Stuart Knight said benchmark azoles (epoxiconazole and prothioconazole) gave 60 per cent control of septoria in a protectant situation and used at label dose.

The multi-site fungicide folpet gave 40 per cent control - not to the level of the azoles, but useful activity nonetheless. The trials also highlighted the continuing value of Bravo (chlorothalonil) in disease control in winter wheat.

Mr Knight said: “It is encouraging to see how effective Bravo is still in a protectant situation, ahead of folpet and doing well in comparison to azoles.

In the trials assessing eradicant activity full label does of Proline (prothioconazole) and Ignite (epoxiconazole) achieved only 20 per cent control in the 2012 season.

There was little difference between SDHI fungicides in terms of protectant activity, but in an eradicant situation Adexar (fluxapyroxad+epoxiconazole) and Aviator Xpro235 (bixafen+prothioconazole) pulled away from Seguris (isopyrazam+epoxiconazole), said Mr Knight.

Protectant activity

Performance of straight SDHI Imtrex (fluxapyroxad) was not as good as that of azole/SDHI mixes.

Assessing results over the 2010-12 seasons, Proline and Ignite showed the same level of protectant activity against septoria tritici.

Performance of Aviator Xpro235 and Adexar was similar, with Seguris slightly behind. A full dose of SDHI gave more than 90 per cent protectant control compared to 50 per cent eradicant activity.

The high yellow rust pressure of 2012 showed the differences between the leading triazoles, with epoxiconazole leading the pack, said Mr Knight. Strobilurins were still doing a good job in terms of yellow rust control and the straight SDHI Imtrex also had useful activity on yellow rust, he said. Aviator Xpro 235 was not as good as Seguris or Adexar on yellow rust, as you would expect, said Mr Knight.

SDHIs were good on brown rust and performed at similar levels, unlike their performance against yellow rust. “It is difficult to go wrong with SDHIs in terms of brown rust control,” said Mr Knight.

Commenting on the performance of azole chemistry over time, he said epoxiconazole had lost one-third of its efficacy at the half dose rate between 1995 and 2012.

The decline in efficacy was less steep for the full label rate, he said. “We can only dream of 80 per cent eradicant control now. It underlines why it was such a struggle to eradicate septoria in 2012.”

The rate of decline seen with prothioconazole was similar. “Even by upping rates, we are not going to get to the level of eradication we had when we started. Clearly we need to support the azoles with other actives, particularly in eradicant situations.”

Chlorothalonil showed no decline in efficacy in protectant situations over the same period.