Fungicide strategy rethink needed to protect crops and chemistry
New disease control tactics using novel and robust multi-site chemistry will not only help protect wheat crops, but also other key fungicides on which profitable output depends.
That was the main message to emerge from a recent conference hosted by Makhteshim Agan UK (MAUK) at Huntingdon, Cambridgeshire.
Stuart Hill, MAUK’s technical and development manager, said the time had come to think about disease management rather than disease control.
As well as risking yield by letting disease take hold in crops early on, chasing disease increased the risk of septoria resistance to vulnerable single-site SDHI fungicides and triazoles.
Protection rather than cure was vital, said Mr Hill. A key part of this strategy was the positioning of folpet, MAUK’s novel multi-site protectant molecule sold as Phoenix*, at the important early timings.
This would build flexibility into the programme and reduce pressure later in the season. The need for both was increasing, said Mr Hill.
The trend to bigger farms meant spray timings and efficacy were more likely to be compromised and often necessitated earlier drilling, which led to higher disease pressure.
In addition, almost 80% of the wheat area was sown with varieties with a septoria resistance rating of 5 or less, and little better for rusts. That, coupled with very uncertain weather at the T1/T2 timings, meant disease could easily get a foothold in crops.
“Only 50% of the UK wheat area receives a GS30 (T0) spray on average – we believe it should be regarded as the foundation spray, as it is vital in limiting inoculum levels,” Mr Hill told the conference.
He advised applying Phoenix at GS30 at 1 litre/ha plus a triazole at half rate, followed at GS32 with a further 1.5 litres/ha of Phoenix plus triazole. Similar programmes in trials had lifted yields by almost 30% compared with untreated plots.
“The multi-site is there to support the single-sites and as such we have seen no antagonism or inhibition of uptake of triazoles or SDHIs, making it the ideal tank-mix partner,” he added. In addition, folpet also provided some preventative and added activity in mix with triazoles on yellow rust and brown rust, both of which could be a serious problem in early spring.
Folpet’s multi-site activity was a useful addition to help protect the chemical growers’ armoury, he said. UK farmers grew 3m ha of cereals, but just four types of chemistry were used to protect them. Triazoles and SDHIs, the two key groups, along with strobilurins, were on average applied to crops five times a season.
“All of these chemicals are single-site – they act on one area of the pathogen to control it, so are much more susceptible to resistance,” said Mr Hill.
Multi-site chemistry had a low risk of breakdown, but was sprayed on average just under once per crop per season. “We think this has to change. Folpet has no recorded resistance problems, despite being used intensively on vines in France for more than 40 years. It remains stable and is the ideal product to offer support for single-site chemistry.”
Neil Paveley, head of plant disease management at ADAS, agreed that multi-site fungicides had a valuable role in protecting key chemistry.
When used as eradicants, the efficacy of prothioconazole and epoxiconazole had fallen to just 20-40% of 1994 levels. Each mutation step in the pathogen only had a small effect, so the reduction in performance had been gradual. However, with no new products in the immediate pipeline, this decline in performance presented a real threat.
SDHI chemistry needed even more protection, he stressed. Data suggested this group was more like strobilurins when it came to resistance. “Strobilurins went from achieving 80-100% control to 20-30% in just a couple of years. There is pretty good evidence that SDHIs are likely to follow this pattern.”
Mixtures with multi-site inhibitors like Phoenix were the most effective way of prolonging the single-site component’s life, said Dr Paveley.
Backing Mr Hill’s advice to use Phoenix at robust levels, he said chasing disease with high doses of single-site ingredients increased selection for resistance. In addition, the mixture component at the lowest risk of resistance – the multi-site fungicide – should take most of the load, he advised.
NIAB TAG technical director Bill Clark said the curative performance of triazoles had been shocking in the high-pressure season of 2012.
Septoria control would continue to rely on both triazoles and SDHIs, and both would be needed to protect each other. But more was needed, either in sequence or in the mix, said Mr Clark.
He believed more complex, multiple fungicide programmes with two- to four-way mixes were the way forward. “In future multi-site fungicides like folpet may look very effective,” he said.
* Folpet is also marketed as Arizona by some distributors.
