White grain disorder unlikely to return in 2023

SARDI sub-program leader Tara Garrard said white grain disorder was caused by the Botryosphaeria species, caused by rain during the growing season.

She said there were a few signs to watch out for.

"Affected heads can have fluffy white fungal growth, sometimes they can have a pinkish colouration," she said.

"The effected grain is then chalky white, so it doesn't have that nice colour that we've got in other wheat and durum.

"It can be very crinkled and pinched - this can be variable.

"Sometimes it's a good weight and looks completely normal on the outside in terms of the structure, it's just the discoloration and natural thickness."

There were a number of cases of white grain disorders across SA and in to Vic last harvest season, Dr Garrard said.

"The northern region (of SA) was 10 times what we saw (in the south) - much worse over there - and a whole range of different issues keep coming up as well," she said.

Dr Garrard said the last time this was seen was in 2011, when there were six samples of grain from affected deliveries in the Upper North of SA, with the infection rates ranging from 1 per cent to 7pc, with an average of 4pc, which was consistent with averages across SA.

The large percentage of grain disorders recorded in 2011 had not been seen until last harvest.

"This was a really rare occurrence, that wasn't easy to predict and with white grain disorder this was the first time since 2011 that we've had significant levels," she said.

It was not the only rare disease to emerge.

"Fusarium head blight had never been an issue in SA before," she said.

"It's a rare event and the likely hood of it occurring regularly is not very high."

Due to the unpredictability of the disorders, Ms Garrard said it was difficult to think of management strategies.

"It's better to focus on it being a rare event that's unlikely to be common," she said.

"In future years, if we're aware it's happened again, there's the potential that head washers could be used in terms of fungicide application.

"Knowing that going into harvest would mean that we can change some of the strategies at harvest, like more thorough seed cleaning and lower acceptance of screenings to get more of the small grains out."

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In February this year a number of grain samples were sent to SARDI to get diagnostics, Dr Garrard said.

"Of the 85 samples, 4pc of those were positive for white grain disorder, caused by the Botryosphaeria species," she said.

"(A further) 45pc had fusarium head blight, mostly that was pseudograminearum and there was a little bit of culmorum, but no graminearum."

She said, as well, about 51pc of the samples that did not test positive to any of the known diseases but were still displaying similar symptoms.

Dr Garrard said there were two clear causes of white grain disorder.

"It's rainfall and inoculum levels and them occurring at the same time as flowering and grain fill," she said.

After a farmer had a grain disorder detected in their sample, there were a number of protocols they could pursue, as early as this seeding season, Dr Garrard said.

"Step one is knowing what's wrong with the grain," she said.

"For seeding this year, you want to know what your germination rate is like and whether the white grain disorder or the fusarium head blight are affecting your grain germinations.

"If you're aware that you've got fusarium head blight on your grain and you're worried that your infection level's quite high, then use a seed dressing to protect against seedling flight."

If a farmer's grain sample does detect a grain disorder it could have economic impacts, Dr Garrard says.

"If the amount of (affected) grain is higher then 1pc in your grain load, then it can get rejected at the silo," she said.

"You can have a rejection at grain receivals and then you can have downgrading of the grain, which means you're moving it into another classification.

"It may only sell as feed rather then AH."

There have been clear signs shown of an early infection of white grain on grain heads, Dr Garrard said.

"Early on in an infection, when you've still got a green head you can see parts of the head that are bleached," she said.

"It tends to be the parts where those spores have gotten in. They will terminate the growth and you'll get a bleached spot in that area."

Overall, there was more foliar disease pressure during the 2022-23 season than normal, Dr Garrard said.

"We know that there was a lot of stripe rust, it was a pretty exceptional season," she said.

"It was a one in 50 season for stripe rust, so pretty out of the norm for that.

"We actually saw quite a lot of infections on heads and the blooms as well, which we don't normally see and powdery mildew - we had great conditions for that.

"That can cause when it's in the air dribbling in grain and darkening of the heads as well."