Disease risk tough to predict

Disease risk tough to predict


Cropping
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PREDICTING the risks of soil-borne diseases is set to be difficult this year, following a dry season in 2017 with relatively low disease pressure.

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SARDI research scientist Marg Evans and research agronomist Blake Gontar were guest speakers at the recent GRDC update held in Adelaide.

SARDI research scientist Marg Evans and research agronomist Blake Gontar were guest speakers at the recent GRDC update held in Adelaide.

PREDICTING the risks of soil-borne diseases is set to be difficult this year, following a dry season in 2017 with relatively low disease pressure.

So, graingrowers are being urged to use tools such as the Predicta B test to better pin down their risk, particularly for eyespot.

SARDI research scientist Marg Evans said seasonal conditions in 2017 meant eyespot expression was limited even when inoculum levels were high.

“With eyespot, everyone looks for lodging as a sign of it, but that doesn’t always occur,” she said. “The other problem is when people have lodging caused by eyespot, they can think kangaroos or sheep have gotten into the paddock.”

Dr Evans said the eyespot pathogen had very slow growth, so it took time to build up in a cropping system.

“Sowing lots of cereals and stubble retention favour eyespot,” she said.

“Eyespot inoculum takes a long time to build up, but it also takes a long time to break down. At Pinery after the fire, even though inoculum levels had been reduced, it was still there.

“Burning could be a strategic one-off tool but I’d be reluctant to suggest getting rid of stubble as a way of dealing with eyespot problems.”

Ways to manage eyespot include getting rid of inoculum, which is not easy to do, and using less susceptible varieties.

“Fungicides are effective but none are registered for eyespot, which is a pain,” Dr Evans said.

“There’s really no resistance in the germplasm in Australian varieties but there are ones that are less susceptible compared to others.”

Varieties such as Trojan or Emu Rock, which are not as affected by eyespot, could be a good fit for growers with a serious problem with the disease.

Dr Evans said there were a number of products in the process of label extension or registration for use in eyespot management. Providing the applications are supported there should be some options available across the next one to four years.

At the moment, registration of Bayer’s Aviator Xpro at 500 millilitres a hectare has been applied for and is expected – but not guaranteed – by the end of May.

Registration of Adama’s Soprano 500 SC at 125mL/ha has been applied for and it could be available by the end of this year.

Adama plans to submit a label extension for Radial at 840mL/ha for eyespot management by the middle of this year, meaning it could be available by mid-2019.

Syngenta expects to have two products with label extensions for suppression of eyespot in place by 2020.

“But at the moment these products are not registered, so there’s no come-back if it doesn’t work,” Dr Evans said.

Dr Evans said crown rot had not caused significant problems in cereal crops across the past few years, so it was difficult to make a general prediction of the risk across SA this year.

“While crown rot often shows up with white heads in the crop, it’s not the case every year, but you do always see stem browning, so always look at the base of the plant,” she said.

Eyre Peninsula-based ​SARDI research agronomist Blake Gontar is conducting research on sclerotinia in canola and eyespot in wheat and management options for their control.

“Both diseases are under researched in our environment,” he said.

“Through our research, we’re looking at different strategies and opportunities for wheat-on-wheat rotations, which are often the most profitable.”

Trials at Yeelanna on the EP are looking at management combinations including varieties with varying levels of resistance and different fungicide timings.

“We want to collect detailed data to explain the relationship between starting inoculum levels, crop development and management strategies,” Mr Gontar said.

He said with the 2017 season’s incredibly late break on the EP, followed by a short growing season, there was a generally low incidence of eyespot.

“But even though we had a low rainfall season on the EP, there were still significant effects of eyespot observed in some areas,” he said.

​Dr Evans and Mr Gontar were both guest speakers at the recent GRDC update held in Adelaide.

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