Early action will be key to preventing yellow rust and Septoria from gaining a foothold in crops this spring, say experts.
The risk of both diseases is relatively high after a mild winter and significant crop area sown early into good conditions last autumn, says David Ellerton, technical development director for agronomy firm Hutchinsons.
“There are plenty of good, lush, early-sown wheat crops around, which will potentially be at higher risk of disease given the right conditions.”
While cold weather and frosts will slow disease development, conditions can quickly change and allow disease to build. This was clearly evident with Septoria in some crops last season, says Dr Ellerton.
A reasonable level of inoculum on older leaves in many crops could develop quickly – and spread to new growth if conditions turn warmer and wetter in coming weeks, says David Howard, Hutchinsons head of integrated crop management.
“Temperatures have been milder than average since last September. It hasn’t been particularly wet, especially in January, but there has been enough moisture to keep disease ticking over on lower leaves.”
Growers are advised to assess disease risk for individual fields to help plan fungicide programmes. Fields and varieties to treat first should be prioritised and crops identified where there may be scope for flexibility on timing, product choice or rate.
Early treatment is paramount for yellow rust control, so this should be the main focus of the first fungicide spray, which Dr Ellerton says should usually be applied to winter wheat around growth stage 25-30.
“It’s important to knock it out early with a tebuconazole or metconazole-based fungicide.” Including a strobilurin such as azoxystrobin or pyraclostrobin, can bring extra persistence but strobilurins should not be used alone.
Susceptible varieties rated 3 or 4, such as Skyfall, KWS Kinetic, KWS Zyatt or RGT Wolverine were hit particularly hard by yellow rust last year. But they will also give greatest yield response to treatment.
Varieties with higher Recommended List ratings cannot be ignored though – not least because adult resistance may not kick-in until late in the season. “If disease establishes early, it can cause significant damage before adult resistance takes effect.”
Yellow rust may be the focus of the first fungicide treatment. But this early spray can also be used to boost Septoria protection in high-risk crops and reduce pressure on later GS 32 (T1) and flag leaf (T2) treatments.