MANAGING septoria tritici blotch (STB), the problematic fungal disease now rated as the major disease in wheat crops in high rainfall zones across the country, is no easy task.
Fungicide resistance is beginning to become a problem, while the nature of the disease’s life cycle means fungicide applications can be problematic due to difficulties with paddock trafficability.
“Getting paddock access when you want to spray can be difficult in the late winter period,” said Southern Farming Systems operations co-ordinator Gina Kreeck.
“The issue of getting onto your paddocks during a wet winter means logistically you are often constrained with what you can do in terms of timing of spraying.”
Speaking at Southern Farming Systems’ Agri-Focus event at Westmere, in Victoria’s high rainfall zone Western District last week, she said the golden rule for farmers was to understand the impact on yield each leaf on the wheat plant had.
“The flag leaf is the major contributor to yield, with each of the earlier three leaves also having reasonably important bearing on grain,” Ms Kreeck said.
“With this in mind, its critical to get fungicide to protect green leaf area when the flag leaf is out.”
However, she said in waiting until later, when the flag leaf has emerged, around Growth Stage 39, the crop could already be under stress from Septoria infection.
“Spraying early can control the epidemic before it gets too bad, but on the flip side it does not protect the most physiologically important leaves for yield, while by leaving spraying late you get the flag protected but the plant is already under stress, so it is a balancing act.”
A two-spray fungicide program can work, but Ms Kreeck said unless farmers rotated fungicides it put further stress on the products.
A seed treatment is also good for early season control, but by early spring, around the first node emerging (GS 31) the effects of a seed treatment have worn off.
Tracey Wylie, of the Foundation for Arable Research (FAR), said Australian cropping was following in the footsteps of the UK industry where fungicide resistance is common.
She said resistance was emerging to triazole fungicides in Tasmania.
“The Septoria pathogen has mutated and there is reduced efficacy there.
“At present triazole products are still working in other high rainfall zones, such as the Western District, but you would expect they will come under pressure there as well.”
She said farmers could use a ‘double knock’ strategy of also including a strobilurin-based product to their fungicide program, which can be done with products such as Radial, which is a mix of both groups.
In terms of timing, she agreed there were pros and cons to various application dates, but added trafficability in paddocks often meant the decision was largely made for farmers.
“Often the situation is get out on the paddocks and spray when you are able to.”
Both speakers said farmers needed to work within an integrated disease management (IDM) framework.
“Just relying on fungicides is not going to be sustainable, rotations will play an important role in keeping Septoria in check, we would not recommend grower go in with wheat on wheat through this area due to the risk of high rates of Septoria infection,” Ms Wylie said.
STB is a stubble-borne foliar disease, characterised by brown blotches containing black spots appearing on the leaves of cereal crops.
It can cause severe yield penalties when left untreated.
The disease had been only a minor problem in Australia until the past five seasons where wet conditions have seen it become a threat to yield once again.
This year it has spread from its high rainfall zone heartland into medium rainfall areas such as the Wimmera in Victoria and the Upper South East in South Australia.