Genetic resistance to fungal disease critical

Genetic resistance to fungal disease critical to securing higher yield potential

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Tim Brown, AGF Seeds, looks at barley at the recent hyper yielding crops field day at Gnarwarre. Photo: Gregor Heard.

Tim Brown, AGF Seeds, looks at barley at the recent hyper yielding crops field day at Gnarwarre. Photo: Gregor Heard.

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Fungicides can play a critical role in controlling fungal disease, but ultimately varieties with better resistance are required.

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VARIETIES more tolerant of fungal disease are critical if Australian high rainfall zone (HRZ) cropping farmers are to achieve the best possible yields.

This is the opinion of Field Applied Research (FAR) Australia managing director Nick Poole.

Speaking at a Hyper Yielding Crops field day at Gnarwarre, Victoria, last month, Mr Poole said there were a limited number of fungicide options available to growers.

"There are really only three main modes of action available, the triazoles, the SDHIs (succinate dehydrogenase inhibitors) and the strobilurins, while there are other products just released or in the pipeline that is where it stands at present," Mr Poole said.

"You only have a limited number of 'shots' in your arsenal fungicide-wise so to get varieties better able to stand up to disease is critical," he said.

He said the goal with fungal disease management was to keep the top four leaves, but particularly the flag leaf, green for as long as possible.

"The best possible scenario would be to have varieties that have enough genetic resistance to get the plant to the flag leaf stage without significant damage and then a fungicide could be applied to protect all the important leaves that drive yield, if the season favoured application."

He said if foliar fungicides were required they needed to be applied in the growth stage 30-39 period covering stem elongation which coincides with the emergence of the top four leaves in the crop canopy.

Application in this period will maximise green leaf retention in these important top four leaves, provided there is sufficient soil moisture.

When foliar fungicides are applied before flag leaf, Mr Poole said there was the possibility in susceptible varieties that another spray would be needed at flag leaf emergence (GS39) to protect the leaves that emerged after the first spray.

The need for the second spray was frequently down to cultivar susceptibility and the level of rainfall following the first spray.

In SQP Revenue, a Septoria tritici blotch (STB) and leaf rust susceptible variety, trial yields last year rose from 4 tonnes a hectare untreated to 9t/ha with a two spray program.

This dynamic changes when considering more resistant varieties.

In trial work, Mr Poole said applying an extra fungicide to more resistant varieties rarely had an economic outcome.

Darcy Warren, FAR senior field research officer, said the two major fungal diseases in southern Victoria this spring were STB and stripe rust.

He said Septoria has been the major concern in recent years, but said that a new pathotype of stripe rust meant popular HRZ varieties, such as DS Bennett and Trojan were now more susceptible to the disease.

Mr Poole said the current stripe rust situation was reminiscent of 2003-05 when resistance in H45 broke down in southern NSW meaning growers were more dependent on foliar sprays.

This year, croppers with much higher yield potential than normal are in the strange position, for mainland Australia, of considering a third fungicide application for their susceptible cereal crops.

Mr Poole said while unusual, the high yield potential meant it could be worthwhile, not only to "top up" the protection of the leaves but to protect the head which can only be protected from head diseases if the spray goes out before the disease is visible.

Along with genetics and fungicide programs, Mr Poole said good paddock hygiene, minimising green bridges to host disease inoculum and a diverse rotation lowered the risk of damaging fungal disease outbreaks.

The story Genetic resistance to fungal disease critical first appeared on Farm Online.

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