SA growers given septoria warning

The National Institute of Agricultural Botany researcher warned SA farmers and agronomists at the recent GRDC septoria technical workshop at Naracoorte that it would be only a matter of time before it occurred here.

He said there had been a dramatic decline in the triazole curative activity in Britain and resistance was continuing to evolve.

Prior to 2004, the triazole group of chemicals were mixed with either chlorothalonil or strobilurins which limited exposure and helped maintain efficacy.

But with the loss of strobilurins which broke down in 2002-03, and the increased number of fungicide applications, increased resistance had been discovered in the triazoles.

He said the curative activity of a single application of Epoxiconazole at flag leaf stage using full label rate had dropped from more than 90 per cent to 30pc in the past few years.

The time frame for Australia depended on their understanding of the chemicals they had available to them and whether they were single or multi-site action, and alternating these modes of action to prolong their efficacy.

He said British long-term yield response showed there were only eight years from the past 28 years when a fungicide program did not pay for itself, protecting at least 1 tonne a hectare of yield, but agronomists were changing their recommendations using chlorothalonil the cornerstone of the chemical armoury early in the season, and triazole groups later in the season.

However, chlorothalonil was not registered for application in cereals in Australia. But Australia had more variable seasons and there was an opportunity in drier seasons to be more flexible with fungicide applications.

"If you are wandering about a paddock at stem extension time and there is a lot of septoria visible, you would be a fool not to do something about it, but if it has been wet and there is no disease visible, remember that it could still have disease active within the leaf but not visible," he said. "Dry weather is the best ally for farmers and can be the key to preventing infection. The skill for us is to get it right those eight years when we don't need to spray, which might be even more for you."