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What is brown rot? How many farmers benefit from the rain while others lose out

Thursday January 6, 2022 - 04:16 AEDT
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Humid weather can cause stone fruit to be infected with blossom blight or brown rot. - ABC

While we are used to weather warnings about storms and heatwaves, recent warnings in Victoria have included the term brown rot. Why?


The Bureau of Meteorology warned this week that rainfall and accompanying high humidity were conducive to a heavy outbreak of brown rot.


This has forced producers and backyard farmers to scour their orchards branch-by-branch in search of any signs of brown rot.


And with the term turning up in weather warnings it has prompted many non-farming people to ask what is brown rot?


What is brown rot?


Brown rot is a fungal disease that breeds in humid, wet weather that affects stone fruit such as peaches, plums, cherries, apricots and nectarines.


The fungus spreads rapidly, and the entire structure of the plant including the flower, branch, leaf and fruit can turn brown and shrivel, making the fruit inedible. 


Agriculture Victoria says infection occurs when the fruit approaches full ripeness and just before harvest. Stone fruit farmers can lose more than 50 per cent of their crop to the fungus.


The disease is widespread throughout Victoria, with major losses occurring in the eastern states of Australia. 


In recent years, improved management practices and effective fungicides have reduced losses.


But it's still prevalent on commercial and backyard farms. 


What causes it?


Agriculture Victoria's Chris Pittock says the humid weather conditions in Victoria this week is a real trigger for brown rot.


"Because of the rain and wetness on the surface of the fruit and leaves, ideally to minimise the disease you need to prune the tree into a vase or open-air structure," Dr Pittock says.


"That way the air can move freely through the tree.


"Otherwise you trap the humidity and the fungus has a private party."


Can you mitigate the risk?


Dr Pittock says growers should clean any mummified fruit off the tree or ground, as it's a source for the disease to spread.


"Any dead wood on the crop or near [it] should be removed, reducing places where the fungus can sit."


He says growers can spray the trees with fungicides before bud burst in order to help prevent brown rot, but not after.


"So what can you do? If the fruit is pretty close to ripening you can consider picking before things progress," he says.


"But it's best to seek advice from your local nursery about what is a suitable treatment."


How to stay fungus-free


Central Victorian orchardist Colin Pickering has tackled issues with brown rot for years in his orchard with his cherries.


But so far this year, the farm is fungus free.


"It happens because the cherries are usually close together," Mr Pickering says.


"Parts of the petals dry and fall off or in among the foliage and create a perfect environment for brown rot.


"We don't spray for it, we tend to go through and open the bunches up [and] pick through what's affected."







- ABC

© ABC 2022

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