Australia
June 6, 2016

With winter crop sowing well underway across New South Wales, wheat growers are being reminded to stay vigilant on stripe rust.

NSW Department of Primary Industries (DPI) senior plant pathologist Dr Steven Simpfendorfer (picture) has two key messages for growers as the season progresses - monitor crops regularly for any signs of rust infection and tailor fungicide strategies to varietal resistance level, rainfall zone, growth stage and seasonal conditions.

Speaking at the Grains Research and Development Corporation (GRDC) Grains Research Updates earlier this year, Dr Simpfendorfer said the stripe rust risk was always present and urged growers not to drop the ball on management, particularly around minimum disease standards.

“The northern cropping region is on track with rust management and growers can’t afford to slip on minimum disease standards. Any perceived short-term gains are likely to result in long-term pain for the whole industry,” Dr Simpfendorfer said.

Stripe rust infection occurs as long as there is leaf wetness of between five to six hours (minimum three hours) with temperatures below 20⁰C (optimum 6⁰C to 12⁰C) – conditions which usually occur overnight during the growing season.

In 2015, stripe rust first appeared in wheat crops in northern NSW/southern Queensland (North Star and Goondiwindi) in moderately susceptible (MS) varieties (Sunzell and Gauntlet) at the start of August. This coincided with cooler autumn/winter temperatures and rainfall which were very conducive to the development of stripe rust in 2015 crops.

There were also numerous reports of stripe rust ‘hot-spots’ in the MR-MS variety Suntop across regions in 2015.

Dr Simpfendorfer said growers should consider ‘up-front’ or early season fungicide management of stripe rust in Suntop in 2016, especially under higher nitrogen status.

“With varieties such as Suntop that rely largely on Adult Plant Resistance (genes that slow down the rate of disease development), consider using an in-furrow fungicide to protect early growth,” he said.

“Flutriafol on starter fertiliser has been shown to provide extended protection against stripe rust in the northern region however it’s a more common component of stripe rust management strategies for susceptible wheat varieties in the southern region.

“Fluquinconazole seed treatment also protects early growth but has tended not to provide the same length of protection as in-furrow treatments in northern trials.”

In contrast, Dr Simpfendorfer said EGA Gregory remains moderately resistant (MR) to stripe rust and does not require fungicide application.

“MR varieties such as EGA Gregory can still develop low levels of stripe rust under high pressure however the level of infection, while visible, does not result in the loss of enough green leaf area to cause significant economic yield loss,” he said.

“If growers had stripe rust in their EGA Gregory in 2015 it is likely to be a seed purity issue and they should consider freshening up their seed source.

“When monitoring crops like EGA Gregory for stripe rust infection, it’s important to recognise the different between a ‘hot individual plant’ and a ‘hot-spot’ before creating panic.

“Individual heavily infected plants scattered across a paddock is indicative of a potential seed purity issue with a moderately resistant crop such as EGA Gregory being contaminated with a more susceptible variety.

“A ‘hot-spot’ is all plants in at least a one metre circle with development of pustules. It occurs due to higher humidity during winter, causing spores to remain in small clumps that are relatively heavy, which limits spread by wind.”

For more information on stripe rust prevalence in 2015 and management implications for 2016 crops, download a copy of Dr Simpfendorfer’s Updates paper `Wheat rust in 2015 – where are we heading?’ by visiting the GRDC website www.grdc.com.au and navigating to the research and development section https://grdc.com.au/Research-and-Development/GRDC-Update-Papers/2016/02/Wheat-rust-in-2015-where-are-we-heading

Website: http://www.grdc.com.au

Published: June 6, 2016