Experts have warned that two wet, high production seasons have masked extensive Fusarium crown rot infection across the northern grain growing region and are encouraging growers to make informed planting decisions to mitigate risk.

Random surveys conducted throughout NSW and Southern Queensland, as part of the five-year Grains Agronomy and Pathology Partnership between GRDC and NSW Department of Primary Industries (DPI), identified significant Fusarium Crown Rot inoculum across the region, with 54 per cent of paddocks in north west NSW showing high levels of infection and an additional 31% recording moderate levels.

Similarly, 45% of paddocks surveyed in southern QLD showed high levels of infections and 33% recorded moderate levels.

NSW DPI Senior Plant Pathologist and renowned Fusarium crown rot expert, Dr Steven Simpfendorfer says the disease has had two seasons to build up in paddocks but has largely remained unrecognised by growers.

“Usually when a paddock has crown rot and the season finishes up dry, the crops will express white heads which is the most common identifier of the disease for growers,” he says.

“During the last two seasons, we’ve seen a unique situation because the wet conditions, especially at the end of the season, have prevented infected crops from expressing white heads, so growers may be unaware it’s in their paddocks.

“Our survey data, looking at cereal crops, has shown that crown rot inoculum has been building up over the last two seasons, so it’s crucial growers are being careful with where they sow and what they’re planting – especially if they’re planning on growing durum wheat which is very susceptible to this disease.”

Delta Agribusiness Consulting Agronomist and Director of Crown Analytical Services, Rob Long, says the Northern Growers Alliance and NSW DPI have conducted trials that recorded average yield losses of 58% in durum wheat when infected with crown rot in conducive years.

“Crown rot can cause significant yield reductions in the blink of an eye when temperatures increase and crops are trying to fill grain,” he says.

Mr Long says the key for wheat growers to mitigate yield losses from crown rot this season was to plant tolerant varieties in paddocks showing the least amount of inoculum.

“It’s more important than ever that growers are testing their soil and stubble to determine the level of crown rot inoculum so they can make informed decisions,” he says.

“This will help them decide on crop and varietal choice and where to plant – if crown rot levels are low, all options are on the table but if readings are high or moderate, they should consider switching to barley, canola, a pulse crop or long fallowing to a summer crop.

“While the start to the 2022 season has been wet, it’s trending to be a drier finish as LaNina dissipates, making it the perfect storm for crown rot expression, so now’s the time for growers to prepare.”

Both Dr Simpfendorfer and Mr Long encouraged growers to test any paddocks that they plan to sow cereal crops in with PREDICTA B, a DNA-based soil testing kit, developed by SARDI, that identifies soil-borne pathogens like crown rot.

“It’s so important growers are using this tool to identify crown rot inoculum levels prior to sowing and it’s even more important they follow the correct sampling protocol when using the kit,” Dr Simpfendorfer says.

“If growers don’t fulfill the test’s criteria of adding cereal stubble to the soil test, they could receive a false positive, so they must follow the steps to avoid potential yield loss.”

You can access the full PREDICTA B sampling procedure, which requires growers to collect both soil cores with added stubble fragments, from the Crown Analytical Services website.

GRDC Crop Protection Manager North, Vicki Green, says GRDC has maintained a commitment to supporting up to date research on crown rot and to promote useful management strategies to growers.

“This disease, especially in seasons like this, can be detrimental to a grower’s profitability,” she says.

“It’s essential that GRDC continues to invest in crown rot management and help growers make more informed cropping decisions to boost their bottom line.”

You can access more crown rot management tips from the GRDC website.