Sclerotinia sclerotiorum, the fungus that causes sclerotinia stem rot in canola, is just like a baby boomer.
Both have been able to flourish – whether it be from post wartime economic booms or a result of tightening canola rotations.
Both have been able to build up stocks – whether by investing in them, or by building up sclerotinia sclerotia (likened to a ‘seed bank’) that can persist in the soil for more than five years to infect future crops.
And perhaps most importantly, both are putting a heavy strain on our systems – whether that be within healthcare or farming.
But could the strain on our farming systems be lightened by controlling sclerotinia through integrated disease management?
CCDM honours student Kyran Brooks has recently looked outside the fungicide box to discover an effective alternative for reducing the sclerotinia inoculum load in the soil.
He found that narrow windrow burning of canola stubble produced very hot temperatures, hot enough to stop fungal growth from sclerotia that have been concentrated in the windrow.
With very few options for managing sclerotinia stem rot besides fungicides, Kyran believes this finding is great news for growers.
“Reducing the number of sclerotia in the stubble and hence reducing the soil’s ‘seed bank’ of sclerotia, will likely reduce disease incidence, and may therefore reduce growers’ dependency on multiple fungicide sprays,” he said.
“If you have a year like 2016 where you get a high level of infection, sclerotinia is a massive pain in the neck, forcing growers to spray multiple times. In this situation, windrow burning could make sense.”
“Also, if you grow canola regularly, windrow burning could prevent sclerotia build-up in the soil, preventing a wipe out in a wet year.”
The results short and sweet
With a project team behind him including CCDM’s Sarita Bennett and Leon Hodgson and AHRI’s Mike Ashworth, Kyran set up a canola stubble trial that was similar to the other CCDM wheat stubble trials (that’s another story).
The trial was at Liebe Group growers Keith and Boyd Carter’s property in Wubin, WA.
Different sizes of sclerotes were placed in the windrow to make sure that size wasn’t an issue. Temperature probes measured the heat within the burning windrow.
The results showed that the heat generated within a canola windrow was significant. Temperatures above 200 degrees were maintained for almost 1000 seconds:
Back in the lab, Kyran then worked out exactly how much heat was required to inhibit fungal growth from large sclerotia (larger than 4mm). The red line dividing the agar plates shows the point where fungal growth is inhibited:
Basically, 40 seconds at 200°C was enough to stop fungal growth from big sclerotia. Further testing found that smaller sclerotia took even less time.
So, in summary:
Does size matter?
According to Kyran, sclerotia size doesn’t matter. He divided sclerotia into three different sizes, below 3mm, approximately 4mm and above 4mm. He found that the larger the sclerotia, the more heat and time was required to stop fungal growth. Even so, Kyran found that the heat generated within a canola windrow was well and truely hot enough to stop any size sclerotia from fungal growth.
So where to next? Figuring out the right harvest height to get sclerotia in the windrow
Kyran is also looking at what height to cut canola, to intercept the most sclerotia in the windrow. He’s looking at all canola types; open pollinator (OP), triazine tolerant hybrids (TT) and Roundup Ready (RR) varieties.
“For instance, if we cut canola at 20cm height, it would be really handy to know what percentage of sclerotia will be above this height for interception,” Kyran said.
After visiting 82 sites across the WA wheatbelt, Kyran is now slicing and dicing the central stem of the plants to measure where the sclerotia lie. Stay tuned for these important results.
Fitting this into a no-till system
Kyran believes that his research fits in well with a no-till system, especially for growers who are concerned about inoculum build-up initiating future season infection.
He said previously, one of the only non-fungicidal control options was deep burial, which can lead to erosion and organic matter loss. Burning narrow windrows will leave most of the paddock unaffected and reduce sclerotia without tillage.
“It will also take a lot of pressure off our important fungicides,” Kyran said.
“With no sclerotinia resistant varieties and only two active ingredients available to control the disease, it is now more important than ever to identify diverse, non-fungicidal integrated disease management (IDM) strategies.
“We need more tools for the toolbox so we don’t over rely on fungicide and hence reduce the risk of resistance.”
Kyran hails from the farming community of Jerramungup, at the south end of WA’s wheatbelt. Upon graduating from an Agribusiness degree, Kyran is one of the first students to begin Curtin’s new Industry Agribusiness Honours Program, which allows him to work as an agronomist while completing his honours program part-time.
Kyran works with CCDM’s Improved Farming Systems program, which focuses on economical integrated disease management strategies to help reduce Australian farmers’ reliance on fungicides.