THE most common disease of oats in WA, Septoria avenae blotch, has the potential to cause up to 50 per cent yield loss in the most severe cases.
As part of the National Hay Agronomy project, the disease was found in more than 90pc of oat paddocks surveyed in WA.
Research trials were conducted by the Department of Primary Industries and Regional Development (DPIRD) in the medium and high rainfall zones of WA between 2019 and 2021 to determine the effect Septoria disease has on the yield and quality of hay.
Several oat varieties, with various resistance rankings, were included in the trials and received nil, partial or full fungicide disease management treatments to establish a range of disease severities.
Among other research, the project involved assessment of the impact of two oat diseases on the yield and quality of oaten hay by DPIRD.
In the study, it was found if Septoria is present from early growth stages, which occurs during continuous oat cropping, and progresses into the upper canopy during conducive spring seasonal conditions, there may be an impact on oaten hay quality.
DPIRD plant pathologist Kylie Chambers said Septoria disease severity was reduced in all the trials by fungicide application, even in the low disease pressure environments in 2019 and 2020.
"In 2021 at Manjimup, where the disease level was moderate to severe, a single well-timed flag leaf fungicide application effectively reduced disease severity and multiple fungicide applications further reduced disease severity," Dr Chambers said.
MORE CROPPING NEWS
"Hay yield was not impacted by Septoria avenae blotch or fungicide treatments to reduce Septoria in any of the trials.
"This result was unexpected given the moderate-high disease level at Manjimup in 2021.
Septoria usually rapidly progresses up the crop canopy and increases in severity in spring with warming temperatures and continuing rainfall.
When spring is warm but drier, the disease development is restricted.
In 2021, Dr Chambers and fellow plant pathologist Geoff Thomas found Septoria severity increased rapidly towards the end of the Manjimup growing season.
However, the period of exposure to high disease severity in the upper canopy may not have been long enough to impact hay yield.
Dr Chambers said the visual and nutritional quality of the hay was improved with fungicide application in 2021, but not in the other years.
"Fungicides reduced the level of diseased tissue and improved the visual quality of the hay," she said.
"Nutritionally, there was no effect of the hay's crude protein or water soluble carbohydrates, but fungicide application decreased lignin and fibre levels and increased digestibility.
"In the season, fungicide application for Septoria gave a positive economic response for hay production."
Leaf rust
During the same period, similar studies were also conducted on oat crown (leaf) rust, which is less common but historically more damaging than Septoria in oaten hay production in WA.
The fungus is carried over on volunteer oats and wild oats from season to season, but does not infect other cereal crops.
The impact of leaf rust on yield and quality of oaten hay was examined at Manjimup in 2020 and 2021 using varieties with varying leaf rust resistance ratings and three fungicide management strategies - untreated, single fungicide spray at flag leaf and multiple sprays for full control.
"Leaf rust severity varied between the varieties, with susceptible varieties, Carrolup and Wintaroo, having significantly higher rust infection severity than the moderately resistant varieties, Mulgara and Williams," Dr Chambers said.
"This research highlights the importance of genetic resistance in varieties, with the untreated plots of moderately resistant varieties showing lower disease levels than the highly susceptible varieties that had full fungicide control.
"In high rust pressure situations susceptible varieties should not be grown."
It was found that single and multiple fungicide sprays showed similar control of rust levels in varieties with partial resistance, while susceptible varieties showed better control where multiple fungicide applications were used.
Even with a minimum of three in-season fungicide applications being applied, rust could not always be completely controlled in the susceptible varieties.
Dr Chambers said leaf rust could significantly impact the yield, colour and nutritional qualities of oaten hay, especially in susceptible varieties, and can have a greater impact on hay yield and quality than Septoria avenae blotch.
"When rust occurs in susceptible varieties, disease development is rapid and multiple fungicide applications may be required to reduce disease severity and preserve yield and quality," she said.
"Growing partially resistant (MRMS) or better varieties can significantly delay leaf rust development and limit its impact on yield and quality.
"Where rust pressure is high, even MRMS varieties may benefit from a single, well-timed fungicide spray to limit the possible impacts on hay quality."
