Predictions of a high-pressure stripe rust season have well and truly come to fruition, with inoculum extremely high across the eastern Australian wheat belt.
Growers have been urged to focus on being proactive with management, especially prior to flowering, to preserve yield and avoid risking withholding periods at harvest from delayed foliar fungicide applications.
At a recent Grains Research and Development Corporation (GRDC) webinar, NSW Department of Primary Industries’ Steven Simpfendorfer told participants that growers have been highly concerned with infection rates, especially considering the disease has been occurring in most varieties at seedling stages, even for those varieties with adult plant resistant (APR) genes.
“This is a social disease and the high pressure has come from a wet summer fallow favouring ‘green bridge’ survival, and early epidemic development whilst in-season from more susceptible varieties have continued to expose neighbouring crops to inoculum,” he said.
“Seedling infections were widespread this year but this doesn’t mean APR genes have broken down – APR is exactly that, it means the resistance genes don’t kick in until the plant gets older, so growers have to support them until the genetics start taking care of managing the disease.
“Even in resistant varieties, with such an early epidemic growers should consider applying fungicide to support young crops and ease disease pressure until the APR genes take over management. They should not wait for APR to kick in; be proactive and manage the pressure within a season.”
Growers with susceptible varieties were under immense pressure to keep infections at bay, especially because the number of active spores is making it extremely difficult to time fungicide applications properly.
“There have been numerous reports of infections occurring 1-2 weeks after spraying. This isn’t a case of the fungicide not working, it’s more that the fungicide was applied outside of its curative activity phase,” Dr Simpfendorfer said.
“If a fungicide is applied more than five days after infection, necrosis and pustule formation can still occur after application.”
Similarly, FAR Australia managing director Nick Poole said while it was convenient to add a fungicide to susceptible crops at tillering when dealing with in-crop weeds, it was less than ideal for disease management.
“A tillering application followed by a flag emergence spray leaves too big of a gap for the disease to cycle and reinfect plants,” he said.
“In a season with such high pressure, growers need to question whether they’re leaving the crop unprotected for too long and consider if additional fungicide sprays are required.
“It’s timing fungicides to keep the foliage of the flag leaf and the next two highest leaves clean that will give you the optimum yield.”
Mr Poole said keeping the “money leaves” clean is difficult using foliar fungicide if disease has been actively developing in the canopy all season but can be achieved with a timely proactive management plan where the gap between fungicide timings during stem elongation is no more than three to four weeks.
In the lead-up to grain filling, Dr Simpfendorfer said it was crucial growers were being proactive with managing susceptible and moderately susceptible varieties and are working two to three weeks back from flowering to limit active spores in wheat canopies occurring during this period.
“What growers should be trying to do is limit head infections by keeping pustules out of the crop’s canopy as they’re coming into flowering,” he says.
“The more spores in the crop, the more head infection may occur, so this is about ensuring growers are being proactive.”
Dr Simpfendorfer said the impact of head infection on yield was dependent on the conditions during grain fill, but more importantly, fungicide applications at this time were ineffective and can risk breaching withholding periods before harvest.
With the Bureau of Meteorology recently confirming Australia will experience the third La Nina in a row this summer, the risk of stripe rust was expected to be high again next season.
GRDC has a range of up-to-date resources to help growers understand the current stripe rust risk and how to manage it.
You can watch the most recent webinar on the GRDC events page.
