Partner e cacy essential to protect fungicide armoury

Partner e icacy essential to protect fungicide armoury

There is a strong cereal fungicide toolbox right now, but we need to protect it to prevent resistance becoming a problem at farm level – that was the message from Bayer’s Dr Andreas Mehl at a recent resistance workshop.

Dr Mehl was reporting on the latest Bayer sensitivity monitoring, conducted by independent research organisation EpiLogic. The company checks the sensitivity of key diseases to the main cereal fungicides each year, on behalf of Bayer, typically gathering over 150 samples from the UK and Europe annually.

The latest AHDB fungicide dose response curves show a further slide in SDHI and azole performance against septoria, no doubt alarming agronomists charged by farmers to preserve crop potential.

But such research is detached from farm practice, and slightly misleading, Dr Mehl noted. “Testing straight actives is a guide to performance, but we shouldn’t overly rely on this data, as no active will be applied as a straight in the eld.

“We have seen a shift in fungicide performance, which is why it is right that we use azoles and SDHIs in mixtures as recommended in FRAC (Fungicide Resistance Action Committee) guidelines. We also must be using them at rates e ective to support each other,” he stresses.

Is it resistance?

The key consideration is whether a shift in sensitivity is resistance, and he considers the best way to determine this is via so-called resistance factors (RF).

A resistance factor is the level of deviation away from key reference isolates – e ectively the ‘baseline’. Dr Mehl would worry if resistance factors exceeded 30 – meaning the EC50 value was 30 times that of the reference isolates in the test.

EC50 values are used to measure drug and chemical potency, the value being the concentration of active required to achieve a 50% level of control. It is the universal method of measurement across the science community.

This approach shows primary azole performance is stable, after a shift some years back. Indeed, UK and Irish prothioconazole septoria monitoring data from the last three seasons being extremely constant.

This pattern is re ected across Europe, he assures – European and Nordic mean EC50 values being 4.1–5.9mg/litre in 2021 and 4.9–6.1mg/litre in 2020. He states that we shouldn’t read too much into this increased sensitivity to prothioconazole, but it does indicate a stable position currently.

When it comes to SDHIs, Dr Mehl reminds that di erences between them were noted in 2019, and that has remained. It was evident that a shift in sensitivity had occurred with ‘tough’ septoria strains like C-H125R being quite insensitive to certain SDHIs. As a result, he considers low doses of SDHI as high risk, unless supported by an e ective partner.

Bixafen is one of the SDHIs impacted. Although some individual RF scores of above 30 were not detected in the UK, they were in Ireland, Germany and Holland, with bixafen having reduced sensitivity against key strains.

But the good news is that those strains impacting bixafen aren’t with uopyram. Here, no individual RF score above 20 was observed. “It is clear that the incomplete cross-resistance between bixafen and uopyram in a product like Ascra (prothioconazole + bixafen + uopyram) is working. Where we have seen a signi cant shift in bixafen sensitivity it hasn’t been noted with uopyram,” he adds.

Similar incomplete crossresistance is seen with iso ucypram, although some individual high RF scores were noted in the UK and Ireland. It doesn’t overly concern Dr Mehl, as iso ucypram is highly sensitive across numerous isolates, and in Bayer trials is approximately 10 times more potent than bixafen. It means that higher RF scores wouldn’t see a dramatic loss in eld performance, but it does need watching, he cautions.

He also observes that Bayer’s ndings are in line with those of FRAC. This showed a stable situation compared to 2020, with most isolates sensitive to fungicides.

Low population of tough strains

Also, tough strains like C-H125R and C-T79N + C-N86S are generally at low population levels, although higher in Holland. It is possible that some mutations are being impacted by tness penalties, particularly C-H125R. It means that whilst present in the population, they are unlikely to become the dominant strain in the eld.

With other wheat pathogens, he is more relaxed – the other “bad guy” in his books being net blotch in barley.

A slow decline has been observed in SDHI e cacy. Again, bixafen has been more impacted than uopyram, and he considers the approval of Ascra for barley most welcome.

But all-important for net blotch control is prothioconazole, and Dr Mehl says growers must do all they can to support it.

At the moment, there is no evidence of resistance – but the reduction in SDHI e cacy is placing prothioconazole under greater pressure.

The addition of uopyram helps, but so could certain strobs. Dr Mehl presented data from 2019–2021 covering strob sensitivity. Sixty- ve per cent of all European net blotch mutants carry the F129 mutation, which has impacted strobs di erently.

“With uoxastrobin, we’ve seen a decline in sensitivity, but full control with tri oxystrobin – except for one unique strain with a tan spot genetic background found in Denmark that showed reduced sensitivity to all strobs. But in 2020 and 2021, full control was achieved, despite our fears of this odd net blotch tan spot twin spreading.”

When it comes to ramularia, he says that azoles and SDHIs are still o ering a level of control, including prothioconazole that had ‘bounced back’ to e cacy levels close to some years ago. He puts this down to potential tness penalties with some key strains.

When asked about the inclusion of folpet, he feels it has a place. “European research has shown adding folpet to Ascra or Revystar enhances ramularia activity. But we have to think about the full disease spectrum, so it is important not to reduce the rate of azole and SDHI to accommodate it,” he concludes. FG

LSPB managing director, Chris Guest, with a range of the company’s combining pea varieties in PGRO DL trials.

Pea varieties bring yield benefits and strong field characteristics

“With ve of the top 10 green pea varieties on the PGRO Descriptive List (DL), LS Plant Breeding o ers growers a wide choice to suit di erent farm conditions and rotations,” comments Chris Guest, managing director of LSPB.

Mr Guest explains: “In the past, some growers have been wary of combining peas because of concerns about factors like standing ability or ease of harvest.

“However, our current varieties have an array of strong eld characteristics such as downy mildew resistance and standing power – and all are resistant to pea wilt.

“Added to that, these varieties have very worthwhile yield bene ts with, for example, LSPB’s green pea Carrington at the top of the DL at 117% (over control of 100%), which is a tremendous increase over the older varieties in the low 90s for yield.

“Looking at our green, yellow and marrowfat pea varieties on the PGRO DL, we o er a range from market leading Bluetime green pea to Akooma, the top yielding marrowfat.” • Bluetime (110) – a market leading, very high yielding green variety, combined with a high downy mildew resistance and good standing power • Stroma (107) – a very high yielding, green variety with high thousand seed weight and good standing power • Blueman (102) – a high yielding, green variety, combined with the highest equal downy mildew resistance, high resistance to powdery mildew and good standing power • Greenwich (102) – a high yielding, green variety with the highest thousand seed weight on the DL and good standing power • Orchestra (111) – a high yielding yellow pea with the highest thousand seed weight and high standing power • Akooma (96) – the highest yielding marrowfat pea on the

DL with an outstanding yield boost over the older varieties and is seen as a real game changer. Mr Guest adds: “We have more improved varieties in prospect from our breeding programme. For the immediate future, newly DL-listed Carrington is the highest yielding pea on the entire PGRO combining pea list (117) with high standing ability plus good resistance to downy mildew – and will be available to growers for spring 2023 sowing.” FG

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Very high seed yields on the PGRO DL High resistance to Downy mildew High standing ability at harvest

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Trio of high yielding varieties for spring pea growers

Mr Holgate commented: “With increased market demand for plant-based protein and good grower premiums available, nitrogen- xing crops – such as spring peas – should catch the eye of many rst-time pulse growers.

“A good pea crop can generate a similar gross margin to a good oilseed rape crop and, given peas are a short season crop, less working capital is required to grow them in comparison to rape crops that can be in the ground for 11 months.

“For those farmers looking to change spring cropping rotations, lower their fertiliser costs and gain a good entry crop for rst wheats, spring combinable pea varieties Greenway and Mikka – both top ve yielders on the new PGRO Descriptive List for large blue / green peas – o er excellent downy mildew resistance, great standing ability at harvest and consistently high yields.”

Lincolnshire-based arable farmer Tim Booth agrees with Mr Holgate’s assessment of Greenway and has high hopes for Elsoms variety, Mikka, which he is growing this spring.

“We grew Greenway in both 2020 and 2021. It established well and looked very good in the eld both years, producing a very thick and dense crop which stood well at harvest. Yields were very good, and we recorded 3.75t/ha for the 2021 crop. This spring we have opted to go with Mikka – another large blue pea variety from the Elsoms stable – and plan to drill 38ha,” he con rms.

Justin Barrett of Askew and Barrett (Pulses) Limited, agrees that Greenway’s consistency and successful track record in Europe should make it a popular choice for UK growers.

“Greenway is a green pea variety that I have seen several samples of throughout the latter stages of the breeding process. As a variety it seems to produce an above average seed size, good colour retention, and both soak and cook performances have been very good. Its size, and the cooking properties it displays, would make it suitable for most markets. A sample with good colour retention would also make it suitable for the premium export and domestic markets,” con rms Mr Barrett.

For those pulse growers interested in marrowfat varieties, Octavia was the highest yielding marrowfat in 2021 PGRO trials, explains Mr Holgate.

“With its suitability for premium export markets, attractive seed shape, unbeatable standing ability at harvest plus the highest protein content for marrowfats on the PGRO Descriptive List, Octavia should be a popular choice with contracts available for 2022 sowing,” he concludes. FG

Three high-yielding varieties from breeder Nordic Seeds, all supported by strong agronomic data, look solid choices for pea growers this year, according to Jack Holgate, break crop and cover crop manager for independent seed breeder Elsoms Seeds.

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