As a nation of cereal growers gears up for the major spring fungicide applications, Dominic Kilburn learns of some of the key crop management issues and challenges ahead
As a nation of cereal growers gears up for the major spring fungicide applications, Dominic Kilburn learns of some of the key crop management issues and challenges ahead.
Looking ahead to the remainder of the spring fungicide campaign which is likely to feature uncertain weather patterns and high disease pressure, and bearing in mind recent fungicide resistance developments, then robust mixes of chemistry are a win-win for all concerned this season, stressed Scotland’s Rural College (SRUC) head of crop and soil systems, Professor Fiona Burnett (left).
“It’s all about the strategic use of cereal fungicides; protecting the azoles and SDHIs, and the use of multi-site products in the mixes which offer additional disease protection and low risk of resistance,” she explained, speaking at a BASF-hosted disease briefing in early March.
“Knowing what we do in terms of potential resistance issues to key fungicides, why would anyone want to use too much of one product, and therefore increase the likelihood of resistance, rather than adopt a sensible anti-resistance strategy with a good mix of the products available?” questioned Professor Burnett, who is chair of the Fungicide Resistance Action Group (FRAG).
With such variability in weather and disease pressure, prediction and management of disease in crops was a real challenge from season to season she pointed out, advising growers that they should use all their past experience combined with in-crop evidence from monitoring, warnings, data and specific site or crop information, to best judge the risks and rewards they were facing each year.
She suggested that front-loading of fungicide programmes would put growers on the front foot in terms of protection of crops, with the potential stewardship benefit of reducing the reliance on products later in the season by not having to ‘fire fight’ to get disease under control.
“All our fungicides for septoria work best protectantly and so that’s where we have to be,” she added.
Professor Burnett said that good timing of applications was everything. “Poor control of disease is sometimes explained by difficulties with timing of applications – advanced seedling crops in the autumn and a mild winter can lead to an early T0 and T1 spray, and then a stretched gap to T2. “Last year yellow rust appearing in crops was the first indication of a stretched window between T1 and T2. The T1 spray went on early and then it turned cold and crops stopped growing causing a delay in the T2 application.
“Careful growth staging when crop walking is essential to achieve accurately timed applications,” she added, pointing out that the control of septoria by azoles, for example, had fallen from 90 to 30 per cent in the past decade when applications were made too late during the latent period of the disease.
As well as providing a reminder that strobilurins are still very active on yellow rust, and can be brought into the mix with azoles and SDHIs, Professor Burnett suggested that varietal choice should also play a key role in the overall disease management strategy employed by growers and agronomists, and selecting a variety with better resistance to some of the key threats such as yellow rust is an important part of an IPM plan. “Variety choice can reduce the risk of yield loss considerably – it’s about looking at the whole package and that starts when you plant the crop,” she said.
Professor Burnett also pointed out that isolates showing resistance to SDHIs were not only causing concerns in wheat crops, but barley too. She explained that in the past few seasons net blotch isolates with reduced sensitivity had been discovered in Europe and the UK, while ramularia isolates with slightly decreased sensitivity had been discovered in Europe in 2015.
“As far as ramularia resistance is concerned, all of the current varieties in use are relatively susceptible to the disease which is damaging to yield and quality, and control is entirely reliant on fungicides,” she commented.
“Mutants are out there and it’s a watching brief,” she added.
In summarising barley strategies for 2016, Professor Burnett said that growers must manage the crop to maximise grain number and potential grain size. “Early T1 sprays retain healthy tillers and more ears, and a T2 application at GS49 prolongs greening, allowing grains to fill to their storage capacity.”
She said that there were plenty of fungicide options available for rhynchosporium; azoles, SDHIs and strobilurins providing activity, as was the case with net blotch. Bravo (chlorothalonil), she highlighted, offered very good activity on ramularia, while SDHI Bontima (cyprodinil + isopyrazam) brought additional actives into the programme.
SDHI Siltra Xpro (bixafen + prothioconazole) provided good broad-spectrum disease control on barley and Adexar (epoxiconazole + fluxapyroxad) or Vertisan (penthiopyrad) + prothioconazole gave similar control of rhynchosporium and net blotch, she pointed out.
“Avoid an over reliance on SDHIs and azoles, as other mixtures are available, and make use of chlorothalonil.
“There is a wider choice of actives for barley than on wheat and so there is more scope for good stewardship,” she concluded.
Tune in to T1
With the reduced efficacy of azoles in a spring fungicide programme, timing of applications has become more critical than ever, said NIAB TAG commercial technical director, Bill Clark (left).
“I’ve been shocked at the lack of understanding of wheat growth stages and leaf emergence by farmers and agronomists,” stressed Mr Clark. “It’s essential that they look at growth stage development across their crops from GS 30 onwards by checking and monitoring continually.
“In readiness for T1 applications, start checking at the beginning of April and get tuned in to it,” he emphasised.
Mr Clark said that in HGCA fungicide performance trials 2011-2013, he had been struck by the variability of septoria protectant control by key azoles prothioconazole and epoxiconazole. “I expected that, as the dose rate increased there would be less variation in their performance but there was a scatter of results – a combination of resistance and poor timing. There was, however, a better performance with well timed applications at full dose rate.
“This variation in performance of the azoles adds to the importance of variety selection, timing and dose rates,” he said.
“Compare this with Adexar’s performance in the same trials and it delivered a higher level of disease control initially, and much less variability than azoles. This gives growers flexibility in dose and timing at T1 and T2 because of the much higher efficacy in the first place,” he highlighted.
“You cannot achieve sufficient eradicant activity with triazoles alone at T1 and T2 so don’t drop an SDHI out of the programme at these timings – just reduce the dose if you must,” he added.
Looking ahead to T2, Mr Clark emphasised the importance of controlling any septoria infection on leaf 2 to reduce disease pressure on the emerging flag leaf. “If there’s no septoria on leaf 3 then this confirms that the T1 spray was well timed. But if there is septoria on leaf 3 or 2, which can overlap the emerging flag leaf, then inoculum is passed across and increases the pressure on the flag leaf thereafter.
“The T2 spray is all about protecting the flag leaf and eradicating anything on leaf 2 and should include a high dose SDHI + triazole at GS 39,” he advised.
Spend or save?
BASF’s business development manager for cereal fungicides, Ben Freer (left), acknowledged the dilemma many growers are facing this spring to ‘spend or save’ in light of continued low commodity prices and tight margins.
He said that the temptation to cut back will be there but he emphasised that an investment in a robust fungicide programme always pays.
According to NIAB TAG data he presented, the mean response to robust fungicide programmes in AHDB Recommended List trials to wheat over the past 17 years was 2.2t/ha. “High responses over that period were more normal than low ones,” he pointed out.“The response to two SDHIs in the programme was still worthwhile even in a low response year in 2015,” continued Mr Freer, “and the profit response to fungicides that year was still there, but it was smaller because untreated yields were larger.”
Trials at BASF’s East Yorkshire, Rawcliffe Bridge site in 2014 and 2015 indicted that the average yield response of a normal fungicide programme versus a reduced programme was +1.21t/ha.
“That equates to a margin over input cost (MOIC) of 54/ha which, across 200ha (500 acres), is 10,800,” he added.
Mr Freer said that it was vital that growers looked at all the key fungicide options at the T1 and T2 timings so that a range of products could provide “mutual support” as part of a resistance management package.
“There are two excellent options for T1 applications, depending on a grower’s situation. Crops at risk to eyespot and for standard septoria and rust situations then Tracker (boscalid + epoxiconazole) at 1.0-1.25-litres/ha + Bravo (chlorothalonil) at 1-litre/ha is suitable.
“For higher disease pressure then 1-litre/ha Adexar (epoxiconazole + fluxapyroxad) + 1-litre/ha Bravo would be more appropriate,” he added.
“I think the eyespot threat is generally underestimated and 30 per cent of wheat varieties on the RL are susceptible to it. So if growers are facing low levels of eyespot and stem-based fusarium, it will pay to include Tracker which, incidentally, has had a five per cent price reduction for this season.
“Where there is a high risk situation for both eyespot and septoria, there is a middle way of 0.75-litres/ha Tracker + 0.5-0.75-litres/ha Adexar + Bravo,” he suggested.
For T2, Mr Freer recommends 1.0-1.25-litres/ha Adexar + 1-litre/ha Bravo in the majority of situations, offering good dose rate flexibility, although 1.0-1.25-litres/ha Librax (fluxapyroxad + metconazole) + 1-litre/ha Bravo is also an option, he pointed out.
Now available through more than one distributor, Librax differs from Adexar in its azole content (metconazole instead of epoxiconazole) – the formulation allowing more of the azole to get into the plant, providing more rapid curative activity with good persistence, he explained.
“If I was a grower with quality milling wheats and planning for a T3 later in the season, then I would go for Librax at T2 because of it being better on fusarium than epoxiconazole,” said Mr Freer, who added that Adexar and Librax had a new ‘greening’ claim on the label indicating that treated crops build yield for longer, helping them to reach their maximum yield potential.
Mr Freer highlighted that Adexar and Librax are also available for barley crops at T1 (GS 31) and T2 (GS 45-59), but he reminded growers that applications can be no later than GS 45 in malting barley.
Both offer good eradication of, and protection against, rhynchosporium and net blotch while also providing additional straw strengthening benefits leading to a reduction in brackling, he concluded.
What is FRAG?
The Fungicide Resistance Action Group (FRAG) was formed in 1995 and comprises experts in fungicide resistance from across the industry, including pesticide manufacturers, government bodies and independent research organisations. Its aim is to gather and interpret reports of fungicide resistance issues and, via consistent messaging, promote practical guidelines on the status and management of fungicide resistance in the UK.
Strategies for disease control in wheat – 2016
– Time treatments to growth stages- Work in as a protectant situation as you can- Tailor dose to risk- Front load programmes- Work as much variety into programmes as possible- Make use of multi-sites- Plan programmes for all diseases and not just septoria – yellow rust and late season fusariums too
Managing fungicide resistance – at a glance
– Follow the statutory requirement to limit the number of applications to two SDHI fungicide-containing sprays per crop
– Always use SDHI fungicides in a mixture with at least one fungicide from an alternative mode of action group which has comparable efficacy against the target pathogen(s)
– Resistance to SDHIs is driven by dose and application number
– Resistance to azoles is weakly driven by dose and strongly driven by application number – this infers you should use the minimum SDHI dose possible and fully support with the azole
– Tank mixing two SDHI fungicides is not an anti-resistance strategy
– Make full use of multi-sites in programmes