Project wraps up but YCS mysteries remain

Industry scientists and growers have worked on the mystery of Yellow Canopy Syndrome (YCS) since it first appeared in 2012 but despite all the effort, major questions remain and more work is needed.

YCS has spread to most of Queensland’s sugarcane districts and sometimes the symptoms are so severe, it has a big impact on a growers’ cane yield and therefore income.

Recently, a major project costing around $10 million dollars was wrapped up by Sugar Research Australia. With the cooperation of growers across many regions, more than 30 scientists and support staff approached the problem from a variety of angles and we thank them for their efforts.

Their final report, available on the SRA website and summarised in the July 2021 Australian Canegrower magazine, reports that no disease, vector, genetic or nutrient link was found to cause what has been described as induced leaf aging.

We do know that YCS interrupts the movement of sucrose from the leaves to the stalk – but the research has not been able to pinpoint why it happens or how to stop it.

The key, though, is plant stress. Basically, YCS will kick a crop when it is already down, and it will usually happen during the peak growing period between December and March.

Once affected, the yellow leaves don’t recover. In the worst cases the stalks become rubbery. That tallies with what growers have seen. YCS will rear its head when there’s been rain after an extended dry spell.

On my farm I have seen too that there is no rhyme or reason as to why one block or area is heavily impacted and another one nearby, just across a headland, is not.

From the SRA research project, the best advice to combatting YCS at the moment is to reduce stress on the sugarcane plants. As growers, we are always trying to reduce stress on our crop because when it is healthy, it grows.

So, I understand growers may feel disappointed by the outcome of the research project. We all like answers and a quick fix. This time, unfortunately, they are not available.

I’m not losing heart. Science constantly develops, new people come up with new ideas and new options can be tried.

It took researchers more than 80 years to identify the cause of chlorotic streak disease, which first appeared in 1929 and is one of the most common diseases in the Australian sugarcane industry. Only in recent times was the DNA of a water-borne organism that spreads it identified.

For this reason, research into YCS must continue beyond the end of this project. SRA says it will continue to invest in YCS and this is critical. We need a form of active, ongoing monitoring and a plan be ready to ramp up research again should anything change.

As with chlorotic streak, just because the cause can’t be found now, doesn’t mean that it won’t be discoverable in the future or that the current level of YCS across the industry won’t change. So, it is important that growers stay vigilant and on the lookout for YCS symptoms.

In the meantime we are left with our questions: What causes Yellow Canopy Syndrome? How do we stop it? And the hope that the future holds the key.

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