With ramularia displaying increased insensitivity to azole and SDHI chemistries, plus confirmed resistance to strobilurins, UK growers must incorporate a multi-site fungicide into their T2 crop protection protocols to ensure adequate disease protection.
That is the advice from Andy Bailey, Fungicide Technical Specialist for Adama, who advises that ramularia mutations have resulted in multi-sites being the only products to offer robust efficacy against this key barley disease.
Ramularia leaf spot can cause extensive damage to the upper leaves of spring and winter barley once crops have finished flowering, resulting in reduced crop quality and yield reductions, with the AHDB citing yield losses of up to 0.6 tonnes per hectare in spring barley.
“UK growers need to be aware that, due to disease mutations, the effectiveness of SDHIs, azoles and strobilurins at controlling ramularia is severely impacted,” Andy Bailey explains.
This leaves multi-site chemistries such as chlorothalonil and folpet as the only remaining options for the effective control of the disease.
“UK populations of the disease have already shown insensitivity and reduced susceptibility to prothioconazole and SDHI chemistries, and we have also seen confirmed widespread resistance (G143A mutation) to strobilurins,” Andy continues. “This is now impacting on field performance with reports of poor control from previously robust programmes at locations throughout the UK in 2017.”
Unlike other modes of action, multi-site fungicides are not affected by resistance and, as such, remain effective against air-borne ramularia. “Using multi-site products is therefore vital to providing effective protection.”
Andy therefore urges growers and agronomists to include a multi-site at the critical T2 timing: “As well as using resistant varieties in areas where the ramularia threat is highest, growers must also factor in a multi-site fungicide at the T2 timing to protect crops from ramularia infection. Folpet, available as Arizona (500g/l folpet), has been shown to reduce ramularia levels, particularly when used in mixture at the T2 timing. Folpet also reduces the pressure on single site active ingredients, many of which are under threat from the re-regulation process, by reducing the pace at which resistance to these chemistries develops.”