Marginal fungicide spray programmes require a re-think in order to tackle growing problems with resistance, according to Prof Fiona Burnett, SRUC.
Using wheat as an example, Prof Burnett told the BCPC Review at NIAB: “It was almost inevitable that we’d experience difficulties when you think flag leaf used to be the absolute key timing in wheat, but now we’re up to seven [fungicide] applications.
“To be talking about T minuses, T0s, T1.5s and T4s is beyond what should be necessary.”
In barley, SRUC trials data showed even in spring crops that T1 timings are most crucial, followed by T2s, but additional sprays including T0 and T4 showed only very marginal benefits.
Prof Burnett said: “With barley we know those early T1 sprays are about setting the potential yield, so that’s a key timing, and the T2s top up that green leaf area. That allows us to focus in on what’s really necessary and take out some the additional sprays that may or may not be necessary.”
The industry now needs to focus on the value of varietal resistance, after coming through a period in which the solution was to treat crops and manage disease heavily, Prof Burnett said.
“We’re seeing resistant varieties coming through and it’s encouraging to see growers picking up more resistant varieties. However, what we’re not seeing is a reduction in the amount of fungicides being used.”
Bill Clark, technical director at NIAB, added: “We’ve done trials at NIAB, and probably a third of varieties on the Recommended List only need two sprays in most years. Yellow rust can still be an issue on these varieties, but this can still be controlled relatively cheaply.”
With new actives set to hit the market next year, it is key that stewarding them and existing products is made top priority, Prof Burnett added.
“Inatreq and Revysol are now very close to use, and we have several new batches coming through including new generation strobilurins and new generations SDHIs, and they need a different mindset.”
Minimising stress in barley crops will be key for controlling ramularia post-chlorothalonil (CTL).
Prof Burnett said: “CTL has been the answer for this year and it may get some of the crop through next year, but the link between ramularia and stress is really going to have to be about a broader process of minimising crops stress and thinking about other actives, maybe working with biostimulants and micro nutrients to treat the crop kindly.”
With sales of chlorothalonil due to finish on November 20, this autumn will mark the last opportunity to buy the active ingredient for use next spring.
Final stocks must be used-up by May 20 2020.