Northern growers at risk of cereal disease misdiagnosis due to seasonal and paddock conditions

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20 July 2022, AU: Northern growers have been anticipating an increase in disease risk with ongoing wet conditions creating the perfect storm for cereal leaf diseases such as rusts, net blotches and yellow leaf spot.

While NSW Department of Primary Industries (DPI) Cereal Plant Pathologist, Dr Steven Simpfendorfer said there have been reports of disease across the region, he’s also seen growers potentially misdiagnosing discolouration and yellowing of crops for things like yellow spot, when it’s actually been caused by waterlogging, frost damage or other plant stresses including nitrogen deficiency.

“The wet conditions have generated a hard situation for growers because there’s massive potential for misdiagnosis of disease,” he said.

“For example, when paddocks are really wet and waterlogged, the soil can lose nitrogen through the process of denitrification, which can cause discolouration in crops when they become deficient in this nutrient.

“A lot of things can make crops go yellow, it doesn’t necessarily have to be yellow leaf spot – so growers need to be getting out in their paddocks to assess circumstances before making a call on fungicide application.”

The Grains Research and Development Corporation (GRDC) and NSW Department of Primary Industries (NSW DPI) have co-invested significantly in assisting growers with diagnosing and managing in-crop diseases and communicating seasonal risk.

Dr Simpfendorfer said unfortunately, signs of a stressed plant can often be similar to a plant with disease and in some cases, growers have treated yellowing crops with a blanket fungicide application because they’ve assumed the discolouration was caused by yellow spot.

“When you consider the price and availability of inputs lately, misdiagnosing a disease could be a significant cost to a grower,” he said.

“It’s so important that growers are walking into the paddock, looking at the root and tiller bases of cereal plants and checking for browning to help diagnose if below ground disease issues such as Fusarium crown rot are associated with the yellowing of lower canopies.

“If they see widespread yellowing of lower leaves in a cereal crops they could also consider applying some urea to the area and watering in then check it again in 5-7 days. That way they’ll know if the main issue is related to nitrogen deficiency.”

Dr Simpfendorfer said there have been confirmed cases of stripe rust, Fusarium crown rot and yellow spot across the north and growers should remain cautious.

“While it’s good to see growers acknowledging disease risk, they should maintain logic when making management decisions and take the time to correctly diagnose disease before treating it.”

If growers suspect they have disease in their cereal paddocks upon inspecting plants, in the first instance they can send high quality photos to Dr Simpfendorfer on 0439 581 672 for rapid advice and then submit plant samples for more detailed diagnosis if required.

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