The sclerotinia management challenge
Moora grower Andrew Nixon is looking at a variety of ways to manage the long-term impact of the fungal disease sclerotinia on his canola production
Three years ago, the fungal disease sclerotinia wiped out 60 per cent of the total yield potential from some of Moora grower Andrew Nixon’s canola crops.
With an average yearly rainfall of between 450 and 500 millimetres, combined with occasional warm late-winter temperatures, canola crops in the Moora district of Western Australia have offered rich pickings for the disease and growers have had a huge task to keep it at bay.
In 2016, with 500mm falling before the end of August, and with a massive canopy creating a humid environment within the crop, the conditions were perfect for the Sclerotinia sclerotiorum fungus to breed, causing an outbreak of the sclerotinia stem rot disease.
These almost-perfect growing conditions forced growers to consider all options to tackle the disease long term.
Andrew says that once the disease takes hold of the plant it is almost impossible to eradicate. “Given the wet conditions we had, combined with some warmer winter temperatures during flowering of between 18ºC to 20ºC which caused high canopy humidity, the sclerotinia was definitely worse than ever before,” Andrew says.
With his cropping program accounting for 95 per cent of business profits, and with 30 per cent of his total farming business reliant on canola production, protecting the crop against this devastating disease has become a priority.
Andrew believes early intervention is crucial, but says with fungicide applications being little more than a preventive measure, it is important to monitor crops closely as soon as flowering occurs. He says in some years, monitoring should occur even earlier than flowering if there is high disease pressure in crops, particularly since the sclerotinia infections can enter through the roots of canola.
Fungicides that contain prothioconazole (Prosaro®), iprodione or procymidone as active constituents comprise some of the only registered chemicals available. “The spray is like a protective coating and if you don’t get the coating on before the plant is infected, you can’t turn back the infection,” Andrew says.
“So it’s about watching the weather and getting the fungicide onto the plant before that period of ideal weather occurs for the disease to spread and infect plants.”
Andrew believes using high water rates from ground application rigs is critical to get under the thick canopy and protect the plant stems. “It’s hard to get canopy penetration from an aerial spraying technique,” he says.
He discovered different levels of the disease on two separate parts of the farm, so two fungicide strategies were applied.
On one part of the farm, as a trial he sprayed 400mL per hectare of Prosaro® at 30 per cent flowering and then undertook a second pass at 60 per cent flowering stage. (The Prosaro® label specifies the full range of flowering time options.)
On the second part of the farm he was able to use just one pass at the 50 per cent flowering stage. “These strategies come at a high cost to profitability, but once the disease takes hold in the plant, there is no cure,” he says.
With two passes costing more than $80 per hectare, attempting to manage the disease for the long term using agronomic and rotational tactics becomes extremely tempting. “Canola is such a significant part of our cropping program, so we are looking at various strategies to minimise the risk of the disease impacting on our total yield in the long term.”
One strategy the Nixons are considering is to widen row spacings (44 centimetres instead of 22cm) to reduce the thickness of the crop canopy, thereby reducing humid conditions in the crop. “There is no clear research data on this strategy yet, so putting this in place in 2017 would be more of an experiment than anything, but it has worked in a similar way with barley,” Andrew says.
Another strategy he is considering is cutting the canola stubble as short as possible, then following up with a stubble burn to kill off the fungi. Changing rotations will also be part of the long-term management plan to reduce the disease’s impact. “Instead of a tight one-in-two-year rotation, we might look at canola every three or four years to reduce our disease exposure.
“Interestingly we’ve been finding that the sclerotinia seems to accelerate after an application of UAN (liquid fertiliser) so now we always make sure we apply the UAN with a fungicide.”
He says that on paddocks where there has not been a tight rotation previously, maintaining the one-in-four rotational intensity will help with tackling the disease.
Department of Agriculture and Food, WA, plant pathologist Dr Ravjit Khangura has been running GRDC-funded sclerotinia canola trials on the Nixon’s property to investigate, among numerous preventive strategies, the effectiveness of different chemical applications to determine the most cost-effective treatment.
While she says disease pressure on the trials in recent years, particularly in WA’s northern agricultural region, has been low, conditions in 2016 were expected to produce significant results from which to guide improved management options into the future.
She is investigating the effectiveness of six different fungicides, all with varying active ingredients, which if proven successful should provide growers with alternatives to the registered chemicals currently available.
Dr Khangura believes one of the most important strategies for growers wishing to tackle the disease is longer rotations, to rid the soil of the inoculum. “Tight canola rotations may have contributed to the rapid build-up of sclerotinia inoculum in paddocks. We used to see this disease in the late 1990s, but infections weren’t very high – but from 2007 onwards the disease outbreaks have been on a much larger scale.
“The fungus can survive in soils for five or six years and it will attack all broadleaf crops, including lentils, chickpeas, faba beans and lupins,” Dr Khangura says.
Another part of her trial is to investigate the effectiveness of wide row spacing for canola crops, something that Andrew is keen to apply on his property.
“I’ve been trying for a number of years to look at the effectiveness of wide row spacings but in recent years we haven’t had the disease pressure to make our results viable,” Dr Khangura says.
“What we have found is that wide rows have no adverse impact on the end yield result of the crop when compared with narrow spacings, so hopefully the high disease pressure seen in 2016 will provide us with results that growers can apply on-farm.”
Another strategy she says that could be considered is burying the fungal sclerotes 10cm or deeper in the soil to prevent their germination, possibly through mouldboard ploughing or spading.
She says growers can also determine the extent of disease infiltration by closely examining their harvested seed: “The sclerotes, which look like small mouse droppings, persist in the soil and can be easily detectable in harvested canola,” she says.
In fact, in WA there is a threshold of 0.5 per cent sclerotes in deliverable loads. This is why Dr Khangura reiterates the importance of sowing canola free of sclerotes to avoid introducing the disease into sclerotinia-free paddocks.
More information:Dr Ravjit Khangura, plant pathologist, DAFWA,
08 9368 3374,
GRDC Project Code UM00051
Region South, West