Earlier this year, AHDB reported that septoria isolates with medium to high resistance to SDHI fungicides had been detected in samples taken from a field site in southern England in 2015.
While there have been no reported field performance issues concerning SDHIs, existence of the mutations in a field situation is cause for concern, says Adama technical specialist Andy Bailey.
“There are still not failures in the field to SDHIs but these are alarm bells. Strobs went very quickly; azoles have had a lot of sensitivity erosions which have been more gradual and happening since 2005.”
While 2015 was not a high pressure year for septoria, there has been a higher incidence of the disease this year.
“It will be interesting to see how things have moved,” says Mr Bailey.
So what can UK growers do to maintain effective control of septoria?
“They need an integrated strategy,” says Mr Bailey.
With effective septoria control being hampered by ongoing concerns surrounding SDHI resistance, Adama Agricultural Solutions will be using this year’s CropTec event to talk to growers about its folpet-based family of fungicides, which the company recommends growers use as part of a ‘belt and braces’ three-way stack of multi-site, SDHI and azole chemistries.
Adama’s technical experts will be on-hand throughout the event to discuss best-use practice for septoria prevention in cereal crops, as well as its range of oilseed rape, roots and potato fungicides and herbicides.
Adama will also be using this year’s CropTec event to promote the responsible use of metazachlor and metaldehyde by focusing on its joint Metazachlor Matters and Get Pelletwise campaigns, as well as Adama’s own WaterAware and SlugAware stewardship schemes.
For more information about any of these campaigns, or to find out more about Adama’s folpet-based fungicides, go to www.adama.com/uk
Pre-2005 the solution was always in a can. If septoria was all over a crop you could spray it.
“Now there is little curative activity with azole chemistry; with SDHIs there is a bit but they are not massively curative. It is all about prevention and protection.”
Consider growing varieties more resistant to septoria and delaying drilling as well as chemical control, he suggests.
“Lay down protection as early as possible so you are not in a curative situation.”
While multi-site fungicides have no curative action, they have an inherently low risk of resistance, explains Mr Bailey.
“They are contact protectants. They don’t go into the plant but sit on the surface and have to come into contact with the septoria to kill it. So good coverage with a well-formulated product is key.
“Folpet inhibits spore germination, energy production in the mitochondria and cell division. Pathogens find it impossible to mutate on so many levels.”
At T1, for example, where growers may need some curative activity from azoles and SDHIs, folpet can help to maximise this, adds Mr Bailey.
“Studies show it does not interfere with the uptake of the other product. Azoles may only have 20% curative activity left against septoria so it is good to make sure that is not compromised by uptake interference. With yellow rust, azoles still work well but speed of activity is important with rust control and any interference/reduction/slowing down in uptake is not good.”
While Mr Bailey argues multi-sites could have a role at all three spray timings, he says they are particularly important at T0 and T1.
“At T0 it is advisable to put down a multi-site partnered with an azole. Certainly, where septoria and yellow rust are a threat. Yellow rust needs an azole.
“The benefit of folpet is it also has useful effects against yellow rust.”
Advising an alternative triazole, an SDHI and a multi-site at T1, Mr Bailey says: “At T1 you need to lay down protection. If you’re not on top of it by the end of T1 you start to lose the battle.”
Recent trials have shown that folpet can have a role in reducing insensitivity of septoria populations to site-specific mode of action fungicides, says Mr Bailey.
“Exposure to azole will select for mutations. Applying epoxiconazole twice, at the full rate, changed the population of septoria to become less sensitive. A tank mix with folpet mitigated that selection pressure.”
A similar effect has been obtained in trials using SDHIs where mixing with folpet can reduce insensitivity of the septoria population, says Mr Bailey.
“These important findings underline the role which folpet can play in protecting both azoles and SDHIs from resistance.”
Growing wheat varieties less susceptible to disease and protecting existing chemistry is key to current and future disease control at Strawson, based at Featherstone House Farm, Bilsthorpe, Nottinghamshire.
In-house agronomist Ian Holmes says the farm’s main focus is on septoria.
“Beyond that it’s yellow rust – there have been more issues with this in recent years. After that the focus is on brown rust and mildew, while ear diseases are an important factor. This year we had very low sunlight and high rainfall in June, so the ear disease complex came back into focus.”
The farming business grows about 620 hectares of wheat, mainly for feed and a small area for milling. Group 4 varieties grown include KWS Santiago and Evolution. Soil types range from light sandy soils to medium/heavy clay loams, with the bulk of arable cropping on medium sandy clay loams. Rainfall is typically 500-600mm a year.
For harvest 2017 Mr Holmes says the farm is planning to grow a similar range of varieties, but with a move towards those less susceptible to disease.
“We plan to grow a reasonable amount of Evolution and are looking at Graham and Siskin. We’ll also continue to grow some KWS Santiago and Reflection; although the latter was particularly susceptible to yellow rust last season it produced a good yield so we have decided to continue with it.
“Using less susceptible, cleaner varieties will be an important part of what we do with disease management going forward.
“There is a limited range of effective product groups left to control septoria and protecting these is a vital part of part of our disease control strategy.”
The farm has a four-spray strategy, with multi-site fungicide applied at T0 and T1. At T0 a multi-site active and a strobilurin is used for yellow rust protection.
“We used to use triazole and a multi-site but moved away from this so we had less reliance on triazoles across the programme and decreased early selection pressure on them.”
At T1 wheat receives SDHI, triazole and multi-site fungicides. This year Mr Holmes used Manitoba (folpet + epoxiconazole), supplied by Adama, as part of the tank mix for two fields he had entered in the Yield Enhancement Network competition.
The rest of the wheat received chlorothalonil as a multi-site with triazole and SDHI based on a mixture to minimise antagonism.
“We hadn’t used folpet before,” says Mr Holmes. “Yield performance and disease control was good relative to other crops and there were no issues either tank mixing or applying it. It appears to be a good option.”
Where yellow rust is a particular problem, Mr Holmes believes there may be an advantage to using folpet because of it having less antagonism in mixes with other fungicides and possible additional benefits in control of yellow rust.
While he says he understands folpet may be more expensive than chlorothalonil, susceptibility of variety and tank mix partner are likely to determine when it is appropriate to use it, he says.
“Having seen it work this year and show good performance I’ll be prepared to look at it a bit more next year.”
He believes agronomists and growers are on board with the importance of using multi-site fungicides to slow down development of resistance to triazoles and SDHIs.
“It’s easy to think the chemical companies will bail us out with the next new product which will sort it out. Black-grass is another good example that there isn’t always a next thing around the corner.”