Researchers sound alarm on disease at Goondiwindi Update

Liz Wells, March 1, 2023

University of Sydney Professor Robert Park.

THREE prominent researchers used their time at the lectern in Goondiwindi yesterday to drive home the message that the upcoming winter-cropping season carries mammoth disease risks, and crops and varieties should be chosen carefully.

Speaking on day one of the Grains Research and Development Corporation Update held in the border town and winding up today, the researchers spoke the about the disease risk presented by heavy stubble loads and infected seed after last year’s wet season.

This has put the pressure on growers and agronomists to come up with a seeding program that minimises disease risk, not easy when northern New South Wales’ preferred rotational crop, chickpeas, is out of favour because of lacklustre price prospects.

While rusts are a clear and present danger for wheat and barley, crown rot looms as the crucifier of milling wheat and durum yield and quality if spring pans out to be a dry one, as is widely expected.

Wet 2022 brings ‘tsunami’

NSW Department of Primary Industries senior research scientist Steven Simpfendorfer said planting quality seed with high vigour and germination rates was essential if growers wanted to minimise disease risk.

“We got hit with a tsunami of diseases last year,” Dr Simpfendorfer said.

“We have to make sure good stuff goes in the ground.”

Following drought from 2017 to 2019, northern NSW and southern Queensland have had three consecutive soft ends to the winter-cropping season that have not been conducive to crown rot, a disease which comes to the fore in hot and dry finishes.

“Our strategy can’t be hoping for another prolonged cool grain-filling period.”

In Queensland, he said the issue could be White Grain Disorder, and in NSW, Fusarium Head Blight, which can be seen at harvest as crown rot, as well as stripe rust in both states.

“Anything with high germination and high vigour will not have fusarium.”

Dr Steven Simpfendorfer.

Dr Simpfendorfer said lack of knockbacks at the sample stand may have given growers a false sense of security about the quality of the grain they delivered in 2022, with pink grain as caused by FHB and white grain from it and/or WGD missed by handlers.

“They didn’t really know what they were looking at at grain receivals.”

Durum is very susceptible to FHB, but milling wheats are not rated for the disease.

Vigilance for rust needed

Dr Simpfendorfer said unseasonably cool temperatures extended the 2022 flowering period for cereals, which was conducive to pathogens.

“A lot of our problems in Lancer was not Lancer breaking down; it was just that we had so much stripe rust around.”

Dr Simpfendorfer said growers cannot afford to plant highly susceptible varieties in rotations in such a high-risk year, and cited a southern NSW example of Vixen with a 40 percent yield loss because of a 10-day rain-induced delay in fungicide application.

He said growth stage 31 was ideal for spraying for leaf disease, but spraying once the crop got to the flag-leaf stage (GS39) was largely ineffective.

“We need to manage it up to GS31-32 then play the season out.”

While one registered fungicide exists for FHB, a reliable treatment for crown rot is not yet available.

To avoid yield losses to fusarium crown rot, Dr Simpfendorfer said sowing once and sowing early was a key strategy.

“Sow at the start of the recommended window; you’ll have a big impact on the amount of crown rot expression you get.

He said the use of sub-standard seed could well force a resow, which will only push the crop into the later window, and make it more susceptible to crown rot, while cultivation to break up stubble only spreads the inoculum.

“At flag leaf emergence, don’t just look for leaf disease; check the base of the plant for browning.

“Not looking doesn’t make it go away.”

Speaking from the floor, Delta Ag Moree-based consulting agronomist Rob Long echoed Dr Simpfendorfer’s sentiments about the amount of disease lurking in the region’s paddocks this year as indicated by PreDictaB results which show high levels of fusarium infection.

“We’re sitting on a ticking time bomb out there,” Mr Long said.

“The trouble is chickpeas are out of the system; there will be wheat on wheat.”

Mr Long said judicious application of nitrogen to ensure growers were “not overcooking” the crop, and inter-row sowing to get away from the heaviest stubble, were two strategies to consider.

He also expects some tillage to occur in coming weeks.

“I think you will see some puffs of smoke as we get closer to planting.”

Mr Long said he was encouraging growers to plant canola and faba beans rather than wheat after wheat if they were not prepared to consider chickpeas in the current market.

“If chickpeas can get towards $550, chickpeas might come into play.”

Dr Simpfendorfer also noted the challenge that chickpeas falling out of many rotations has presented for disease management.

“Chickpeas have come out of rotation and there’s a lot more cereal on cereal.”

Caution needed for barley

Qld Department of Primary Industries and Fisheries principal plant pathologist Lisle Snyman said the major barley diseases seen in 2022 were powdery mildew and leaf rust.

Dr Snyman said powdery mildew did not “fizzle out” with the season as it normally did, and can reduce yields by 5-15 percent.

“We saw crops with powdery mildew in the head last year which is something we’re not used to.”

Dr Snyman said resistance to powdery mildew has broken down in varieties including Rosalind, Commander and Spartacus, with most of those varieties being European and having one resistance gene.

Like net blotch, smut is a seed-borne disease, and Dr Snyman said loose smut was an issue in varieties with Hindmarsh lineage.

“Make sure you use treated seed.”

She said careful variety selection, as well as crop rotations, were preferable to relying only on in-crop spraying.

“Can we put all our emphasis on fungicides to control diseases, and I think the answer is definitely ‘no’.”

Dr Snyman was critical of preventative fungicide applications when disease was not present, and applications when disease had galloped away.

“If you have really high levels of disease, you could have resistance that could multiply.”

She said planning ahead, and possibly ordering fungicide in advance, based on the seasonal forecast and crop outlook was critical.

“If it’s going to be a high disease load, think about what fungicides you’ll want to spray and when you’re going to need them.”

Exotic threats, local presence

University of Sydney Professor Robert Park warned of self-sown cereals as well as weeds as being the “green bridge” for carrying inoculum into this season, and the need to destroy it with herbicides or heavy grazing four weeks prior to planting.

“I think the outlook for the current season is there’s going to be plenty of rust out there,” Prof Park said.

“In the next year or two, we’re going to find new pathotypes.”

Prof Park said exotic incursions and their hybrids were making it harder for growers to control leaf rust, and for breeders to provide a genetic package that could withstand them.

“Now instead of looking at one genotype, we’re looking at three or four.

“This makes messaging more complex.

“I’d say you’re better off to plan for a worst-case scenario.”

He advised growers to optimise the timing of fungicide applications.

“Rotating fungicides with mode of action is also important.”

This graph shows the increased number of strains of wheat stripe rust found in eastern Australian in recent years. Image: National Cereal Rust Survey/University of Sydney.

He said wheat stripe rust strain 239, which arrived in 2017 from Europe, caused “a fair bit of surprise” in Vixen, Rockstar and Scepter wheat varieties, and 238 was the one that extended its footprint last year.

“It was probably the dominant pathogen in eastern Australia.”

Mr Park said what appears to be a hybrid of 238 was now being seen.

He said 238 had not broken down resistance in any particular variety.

“We believe being a hybrid, it’s got a bit of hybrid vigour.”

The University of Sydney conducts the Australian Cereal Rust Survey, and Prof Park has put the call out early for samples so that pathogens can be identified and traced.

“If you have growers with foliar leaf rust in barley or wheat, can you please monitor and let us know the success or otherwise of these fungicides.”

“We rely upon you folks to send us samples.”

Prof Park said pathotypes can travel extensively within Australia, and not just in wet years, as was seen with the 198 strain which arrived in 2018 from Europe or South America.

“In 2018, even in a drought year, it went from Tasmania all the way to Sydney.”

The following year, 198 crossed into Queensland.

Confirmed cases of wheat stripe rust strain 238 in 2021 and 2022. Image: National Cereal Rust Survey, University of Sydney.

Prof Park said while genetic resistance was the foundation of rust control against local pathotypes, the arrival since 1979 of exotic strains from Europe and the Americas has clouded the picture for not just breeders.

“They’ve created a lot of confusion amongst growers and agronomists.”

“There are rust isolates that came into Australia from somewhere else.

“We can pick them because they’re very very different.”

He said clothing can be a vector.

“It’s a problem because people are travelling more, and spores can remain viable for up to two weeks.”


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