STB warning bells sound
Rust has taken a back seat as the primary disease for wheat in the high rainfall zone (HRZ) of south-eastern Australia with Septoria Tritici Blotch (STB) taking the reins as the biggest headache for growers over the last three seasons.
Foundation for Arable Research Australia (FAR) managing director Nick Poole said in long season scenarios with wetter environments, STB was a lot harder to control than rust.
“It has a much longer latent period (time between fungal spores infecting the crop and symptoms appearing), meaning you can’t tell whether new tissue is infected since it takes longer for the disease to reveal itself in the crop,” Mr Poole said. “You can think the crop is clean, but it’s not.”
Mr Poole said STB is a “big worry” with parts of southern Victoria having fungal populations with mutations conferring resistance to foliar fungicides. He said growers were likely to see more of it.
“The more we use fungicides, particularly the triazole fungicide, the more we will struggle to control STB,” he said. “In NZ, strobilurin fungicides are no longer effective on STB. The thing about the triazole fungicides – which are the backbone of our disease control programs – is that the shift takes place in small steps, making the disease less sensitive to the fungicide over time.
“It’s quite a complex form of resistance, meaning paddocks in Hamilton might have different strains to the ones in Naracoorte. That means the triazole that works best in Hamilton might be different to the ones that work best in Naracoorte.”
Mr Poole said growers need to consistently look for an integrated approach to managing STB that includes more than one option to reduce risk of the disease. This could be achieved with more resistant cultivars, particularly with the earlier sowing dates where disease pressure was higher. He said it was important to use fungicide mixtures and avoid an excessive number of applications in any crop.
In terms of spray timings, Mr Poole said two sprays would cater for most disease outbreaks.
“A first spray at growth stage 31-32 and a second spray at flag leaf itself will control most disease problems in wheat,” Mr Poole said. “In barley it’s not much different, the only difference being to apply the first one at GS30 - 31, always ensuring we don’t stretch our timing between the first and second spray to more than four weeks.
"But with both wheat and barley, when you apply the first spray, it doesn’t mean you have to apply the second spray. You can use those four weeks to see what’s happening in the crop canopy and determine whether disease pressure warrants the need for another spray.”
View a video with Nick Poole explaining more about STB (also linked above)
GRDC Project Code DAN00177