Growers must be proactive to manage increased stripe rust pressure

10 October 2022, AU: 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.

The Grains Research and Development Corporation (GRDC) conducted an online webinar on wheat stripe rust last week to update growers on pathotype frequency across the northern region and how to manage infections at this stage of the season.

Over 350 growers and advisers tuned into the webinar, which featured updates from the University of Sydney’s Robert Park, FAR Australia’s Nick Poole and NSW Department of Primary Industries’ (NSW DPI) Steven Simpfendorfer.

Dr Simpfendorfer says 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 says.

“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 are 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 says.

“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 says while it is very convenient to add a fungicide to susceptible crops at tillering when dealing with in-crop weeds, it is 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 says.

“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 says 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 3 – 4 weeks.

In the lead up to grain filling, Dr Simpfendorfer says it is crucial growers are being proactive with managing susceptible and moderately susceptible varieties and are working 2-3 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 and treating the risk 2-3 weeks prior to flowering.”

Dr Simpfendorfer says the impact of head infection on yield is dependent on the conditions during grain fill, but more importantly, fungicide applications at this time are ineffective and can risk breaching withholding periods before harvest.

With the Bureau of Meteorology recently confirming Australia will experience the third La Niña in a row this summer, the risk of stripe rust is expected to be high again next season.

Mr Poole says while it’s important growers manage their varieties with fungicide properly, using the correct timing, the most significant thing that’s going to take pressure off the system is selecting varieties with a higher level of resistance.

GRDC Grower Relations Manager – North, Graeme Sandral says the industry anticipated that this season would be a 1-in-50-year epidemic for stripe rust and GRDC has focused on extending information and assistance to growers to help manage the risk.

“We conducted our most recent webinar to help growers understand what’s going on in terms of stripe rust risk. Due to ongoing wet conditions which caused a very wide sowing window, crops are at all different stages of development, so we wanted to help them understand how to best prevent and manage infection to maximise profits,” he says.

“This disease costs the Australian grains industry $120 million on average annually. It’s a huge issue for growers, especially in years like this, so GRDC has focused on investing in disease management and making growers aware of the risks.

“Managing this disease is about the industry working together to adopt more resistant varieties and staying on top of management throughout the season. GRDC will continue to spread these messages to growers and support them in controlling disease risk throughout the current and following seasons.”

GRDC has a range of up-to-date resources to help growers understand the current stripe rust risk and how to manage it.

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