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Research targets STB management in southern region

Dr Hari Dadu with a spore trap at the Agriculture Victoria Horsham SmartFarm.
Photo: Grant Hollaway, Agriculture Victoria

Improved strategies for the management of Septoria tritici blotch (STB) of wheat in the southern region will be available from new and ongoing GRDC-supported research being undertaken by Agriculture Victoria, the South Australian Research and Development Institute (SARDI) and Field Applied Research (FAR) Australia. The increasing threat posed by the risk of resistance to fungicides makes the development of a range of management strategies to this important disease critical for growers.

Agronomists and growers in the southern region’s low and medium-rainfall zones have raised concerns about the increased prevalence of STB and its impact on yields in their region. The disease was recently listed as the most important wheat disease in the southern region by GRDC’s National Grower Network.

In high-rainfall zones, STB is a damaging disease of wheat crops where, in most seasons, it can cause yield losses of up to 60 per cent in susceptible varieties if no other control is used. In these zones, STB requires strategies for its management in most years. In medium and low-rainfall zones the disease is widespread, but its impact on yield and the seasons that cause losses are less understood, which makes effective management decisions difficult for growers.

If growers know the conditions under which STB will cause damage, they can make better-informed decisions on if and when to manage this disease.

GRDC’s new investment research, led by Dr Grant Hollaway at Agriculture Victoria, Horsham, in partnership with Dr Tara Garrard at SARDI, Adelaide, will target STB in the medium and low-rainfall zones across Victoria and South Australia.

“We have little knowledge of the impact of STB in the low and medium-rainfall zones,” Dr Hollaway says. “Our research aims to understand the potential impacts of STB on yield and quality and to understand the seasonal conditions when the disease is likely to have an impact, so that growers can implement timely control if necessary.

“If growers know the conditions under which STB will cause damage, they can make better-informed decisions on if and when to manage this disease.”

Yield loss trials

Agriculture Victoria research scientist Dr Hari Dadu says yield loss trials in medium and low-rainfall zones in Victoria and South Australia will be conducted for three seasons (2021–23).

“These field trials will help us understand the extent of yield loss caused by STB in varieties with different levels of resistance in different seasons. Using this information, growers will be better-informed about potential losses in the varieties they are growing,” Dr Dadu says.

In addition to conducting yield loss studies, there is a focus on understanding the environmental conditions that result in yield losses. The project team are using spore traps to monitor spore release from stubble and disease development on wheat grown in a range of locations across several years, Dr Garrard says.

“The team have established spore traps at five locations across the southern region: Birchip, Horsham and Hamilton in Victoria and Hart and Booleroo Centre in South Australia. The spores from the traps are then processed using SARDI’s PREDICTA® B technology that both identifies and quantifies the spores released over time,” she says.

“We will be able to combine the information on climatic conditions, timing of spore release and disease development to inform decision-support tools to help growers target STB management only in those seasons when it is necessary.”

High-rainfall zone

GRDC’s second investment focuses on the high-rainfall zone and is led by FAR Australia’s Nick Poole as part of its research into hyper-yielding crops.

Mr Poole says field trials will be conducted at Gnarwarre in Victoria, Millicent in South Australia and Hagley in Tasmania over the next two years.

“This project aims to demonstrate integrated management of STB in the high-rainfall zone and will target key tactics to guide grower decision-making with a focus on variety choice, stubble management and optimal and conservative fungicide use and timing,” he says.

With the increased threat of resistance to fungicides within the STB pathogen, he says, it is critical that growers have access to a range of effective strategies to prevent losses from the disease.

Resistance screening

Resistant varieties, when available, are a powerful tool for growers who want to manage STB. With support from GRDC, Agriculture Victoria developed a field-based disease screening nursery that is now used annually by the National Variety Trials (NVT) and major plant breeding companies.

A lack of varieties with resistance was a factor that contributed to the high levels of STB developing in the southern region, Dr Hollaway says. A solution was to develop a program that could screen thousands of lines each year for STB resistance and support breeders to develop more resistant lines.

Melissa Cook

Melissa Cook hand-sowing the Septoria tritici blotch disease nursery at the Agriculture Victoria Hamilton SmartFarm. Photo: Grant Hollaway

Following support from GRDC to develop a field-based screening nursery at Agriculture Victoria’s research farm near Hamilton, about 5000 lines are now screened annually for their reaction to STB in the field, according to Agriculture Victoria research scientist Melissa Cook.

“Most of Agriculture Victoria’s disease nurseries are run at Horsham, but for STB the work is undertaken at Hamilton as this provides an ideal environment for this disease and also reflects the environment where resistance is most important,” Ms Cook says.

Most of the lines tested in the nursery are for major plant breeding companies, which want to improve the disease resistance levels. This shows that they recognise the importance of the disease to growers in the southern region.

“The STB field disease nursery also includes lines from the GRDC’s NVT program each year. This helps growers understand the level of resistance in their varieties and to select new varieties with improved resistance to this disease,” Ms Cook says.

“Each year, disease resistance ratings from this nursery are published in state-based disease guides and on the NVT website.”

Fungicide resistance

Fungicide resistance is common in STB in the southern region. Growers in the high-rainfall zone have been dealing with increasing levels of reduced sensitivity to Group 3 fungicides (triazoles). Recently there has also been a report of resistance to Group 11 fungicides (strobilurins) in the southern region.

Dr Hollaway says these findings highlight the importance of growers following Australian Fungicide Resistance and Extension Network recommendations when using fungicides for the management of all diseases, including STB. These recommendations include:

  1. Avoid susceptible crop varieties.
  2. Rotate crops – use time and distance to reduce disease carryover.
  3. Use non-chemical control methods to reduce disease pressure.
  4. Spray only if necessary and apply strategically.
  5. Rotate and mix fungicides and mode of action groups.
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