Key points

• Fungicides used to protect canola against disease in 2020 did not always lead to yield gains
• Despite reducing disease levels, few treatments were cost-effective
• Fungicides may have provided ‘insurance’ against disease, but at a cost
• Three trial sites showed little yield response to any application of fungicides and none that covered the costs of applications, despite a number of diseases being present
• Two treatments at Kamarah (near Ardlethan) and four treatments at Temora did increase gross margins after fungicide application

Applying fungicide to manage canola diseases during 2020 did not always lead to a yield response in areas that typically receive low and medium levels of rainfall.

Grain Orana Alliance (GOA) chief executive officer Maurie Street shared these findings at the 2021 GRDC Update at Wagga Wagga, New South Wales.

He told those gathered that Brill Ag and GOA established five canola trials in southern and central NSW during 2020 to determine the yield response to different fungicide treatments.

“The argument for applying fungicides during spring is a lot clearer in high-rainfall areas where there is a higher frequency of canola in the crop rotation and high yield potential,” Mr Street said.

Grain Orana Alliance chief executive officer Maurie Street. Photo: Nicole Baxter

“It’s not clear if there will be a benefit in low and medium-rainfall areas when there is above-average rainfall, as was the case in 2010, 2016 and 2020.”

He said an absence of trial work on the financial merits of applying fungicides to canola in low and medium-rainfall areas led to experiments in 2020 with GRDC investment.

The replicated and randomised trials, at Ganmain, Kamarah (near Ardlethan), Temora, Warren and Wellington, tested several fungicides (Table 1) and their application timings.

Key diseases targeted with foliar fungicides were Sclerotinia and upper canopy blackleg infection. Alternaria black spot and powdery mildew were also present in most of the trials.

Miravis® Star was applied under a research permit. It is currently under evaluation with the Australian Pesticides and Veterinary Medicines Authority. The researchers monitored the impact of each product on Sclerotinia and blackleg.

Table 1: Fungicide products used in five canola response trials in NSW during 2020.

Source: Maurie Street, Ben O’Brien and Rohan Brill

Fungicide was applied when canola was at 30 and 50 per cent bloom. An application was also made at 10 per cent bloom in three trials as many nearby crops were being sprayed at 10 per cent bloom.

Crops were assessed for disease at maturity and harvested using a plot harvester.

Disease observations

Petal tests (by the Centre for Crop and Disease Management) confirmed Sclerotinia was present at all sites, however, there was no infection on the main stems of canola plants at Warren, low infection levels at Wellington, some infection at Kamarah and Ganmain, with the highest levels recorded at Temora.

In the case of upper canopy blackleg infection, symptoms ranged from negligible at Warren (even in untreated plots) to levels that may have caused some yield loss at Kamarah (Pioneer® 44Y90 CL) and Temora (Pioneer® 45Y91 CL). Both cultivars planted at Kamarah and Temora had no major gene resistance to blackleg infection.

Alternaria infection on pods was most prominent at Warren and Wellington. There was generally less Alternaria infection at the three southern sites.

Powdery mildew, levels were high in the northern sites (Warren and Wellington), low in the south (Ganmain and Kamarah) or absent (Temora).

Climatic conditions

Mr Street said the timing of rainfall in relation to fungicide applications likely affected disease progression.

“Looking back, there were dry periods at most sites that occurred during mid-flowering,” he said. “But in all cases, there was good rainfall through the early and later flowering stages.”

Ganmain results

At Ganmain, all treatments at the 30 and 50 per cent bloom stage reduced Sclerotinia compared to the untreated control, however the 10 per cent bloom fungicide treatment did not reduce incidence.

There was some reduction of upper canopy blackleg disease incidence on branches at the 10 and 30 per cent bloom stages with Aviator® Xpro, but second applications did not reduce disease symptoms.

Mr Street said a single application of Miravis® Star (a new product not yet registered) at 30 per cent bloom also reduced blackleg symptoms.

“The Ganmain crop was HyTTec® Trophy, which has effective major gene resistance to blackleg (resistance group ABD). This provides some reduction in the severity of upper canopy blackleg infection,” he said.

“Another factor that reduced infection risk of the Ganmain crop was that it flowered later in drier conditions, which reduced the potential for upper canopy blackleg infection.”

Overall, despite fungicide reducing the expression levels of multiple diseases, Mr Street said there was no impact on grain yield at Ganmain.

Kamarah results

At Kamarah, the application of fungicides showed a positive grain yield response (up to 0.4 tonnes per hectare) to all single-spray treatments, except Prosaro® applied at 50 per cent bloom. There was no additional grain yield benefit when applying a two-spray strategy.

Mr Street said Sclerotinia infection on the main stem was low, but all treatments reduced the incidence of the disease, except the single applications of Prosaro® or Aviator® Xpro at 50 per cent bloom.

“With the exception of Veritas®, fungicide application at 30 per cent bloom reduced upper canopy blackleg infection on branches from levels that would likely have reduced yield in the untreated control,” he said.

Mr Street said the period between 30 and 50 per cent bloom was relatively wet at Kamarah, which may have contributed to higher branch blackleg infection than at Ganmain.

“A further contributing factor is that the variety Pioneer® 44Y90 CL (resistance group B), despite having effective crown canker resistance, does not have effective major gene resistance,” he said.

Temora results

Mr Street said there was a positive grain yield response of up to 0.6t/ha at Temora.

“Aviator® Xpro at 10 and 30 per cent bloom, but not 50 per cent bloom, improved yields, as did Miravis® Star at 30 per cent bloom,” he said.

“Prosaro® at 30 per cent did not increase yield but did at 50 per cent bloom. A two-spray strategy generally produced good reductions of Sclerotinia and blackleg, but no two-spray treatment resulted in higher grain yield compared with the single application of Aviator® Xpro at 30 per cent bloom.”

He said application of Aviator® Xpro at 10 and 30 per cent, Miravas® Star at 30 per cent bloom and all the two-spray strategies reduced upper canopy blackleg infection on branches, but the best treatment still only reduced the disease score to a range from 1.5 to 2.1 (with 4.0 the highest level of infection).

“A two-spray strategy generally provided good reductions of Sclerotinia and blackleg, but no two-spray treatment resulted in higher grain yield than a single application of Aviator® Xpro at 30 per cent bloom.”

He said the results also showed no impact on oil.

Warren results

At Warren, there was no Sclerotinia or upper canopy blackleg infection on branch or stems.

Mr Street said Alternaria infections were very high. “A couple of treatments only gave a small reduction in Alternaria severity."

Nonetheless, no fungicide treatment improved grain yield.

Wellington results

At Wellington, the results showed a positive (0.2 to 0.3t/ha) grain yield response for two of the two-spray fungicide treatments, Mr Street said, but no single-spray treatments increased yield.

“Sclerotinia infection levels were low and upper canopy blackleg infection levels were moderate,” he said.

“All fungicide treatments except Prosaro® and Veritas® at 30 per cent bloom provided a reduction of Sclerotinia and upper canopy blackleg branch incidence.”

He said Alternaria infection levels in the untreated control were high on pods and stems, with best reductions from the single Aviator® Xpro 50 per cent bloom application.

““Fungicide application did a better job of reducing Alternaria on the stems than on pods due to the inability to spray fungicide beyond the 50 per cent bloom stage to protect all pods,” he said.

“The large differences between Alternaria scores on the stems did not lead to major differences in grain yield, indicating that infections may have only been superficial.”

Financial impacts

Mr Street said there were only two treatments at Kamarah and four at Temora that offered a financial benefit to fungicide application compared with the untreated controls.

“At Kamarah, the net benefit over the untreated control was $160 to $190/ha, while the Temora site showed a more handsome net benefit of $240 to $320/ha,” he said.

“Of the six fungicide treatments that showed an economic benefit, four of them were single-spray applications, indicating the additional expense of a second spray was not warranted under the 2020 conditions at Kamarah and Temora.”

In 2020, Mr Street said a period of dry weather during late August and early September may have stifled disease development and expression.

“There was no massive collapse in grain yields as a result of not applying fungicide,” he said.

“The difficult part is predicting the weather conditions during flowering and in some cases the forecast can suggest control action is appropriate, however small changes in the conditions experienced at this time can impact infection levels and economic response.”

In the past decade, there had only been three years in central NSW that would support the development of canola disease, with 2020 showing no economic benefit from applying a fungicide in this region.

“In 2020, for three of the five sites, fungicide wasn’t a good investment. Accordingly, funds may have been better put into nitrogen or improved varieties,” he said.

Top tips

In the research paper outlining the results, Brill Ag’s Rohan Brill, Mr Street and Ben O’Brien from GOA, say management factors that reduce the requirement to apply fungicide during flowering include:

• selecting varieties with effective major gene blackleg resistance. Monitor updates to GRDC’s Blackleg Management Guide to assist decisions;
• matching phenology and sowing date so crops do not flower too early. Early flowering usually results in greater exposure to disease (especially upper canopy blackleg infection);
• closely monitoring short-term weather forecasts as diseases require favorable conditions for infection;
• using decision-support tools to quantify canola disease risks and the need for fungicide applications. These include the SclerotiniaCM and BlacklegCM apps for tablet devices;
• avoiding sowing canola in or near paddocks that have had high levels of disease infection recently; and
• if applying fungicide, spray at the correct time (30 per cent bloom) and with good spray coverage to avoid needing a second application.

More information: Maurie Street, 02 6887 8258, maurie.street@grainorana.com.au