T2 wheat sprays dominated by SDHIs this season

T2 sprays will be dominated by the SDHIs, but triazoles remain an essential component of the flag leaf spray, agree leading agronomists.

And where rusts – especially brown rust – remain a concern as the season progresses, the advice is for growers to leave room in the T2 budget for adding a strobilurin, especially where susceptible varieties are being grown.

The good news is that there’s a greater choice of fungicides than ever, says Patrick Stephenson, chairman of the Association of Independent Crop Consultants (AICC) and NIAB TAG’s northern regional agronomist, who believes this crowded marketplace will work to the grower’s advantage.

That’s because there is pressure on fungicide budgets, he reports. “After two indifferent harvests, money is an issue. So the chance to span both T2 and T3 in one spray will be tempting, but it’s a very high-risk strategy and one I would be wary of.”

NIAB TAG trials show it isn’t possible to equal the performance of two sprays with one “boosted” or combined application, he says.

“Having invested £40/ha on the flag leaf spray, only to discover you have to spend another £20/ha on the ear a few weeks later can be unwelcome,” he says.

“That’s why there’s a temptation to combine them, spray at T2.5 and spend £50/ha.”

Alternatively, some growers will be considering a slightly earlier T2 spray, at GS37 instead of GS39, believes Mr Stephenson. “This is timed to coincide with the flag leaf starting to come out, which is less risky than trying to combine T2 and T3.”

Chris Bean, technical director of Zantra, is also of the opinion that waiting to apply a T2.5 spray, when the ear is pushing through, is inviting trouble. “Unless it’s a very low disease year, which we can’t forecast at this stage, it really isn’t advisable. You will compromise ear disease control.”

While much will depend on what has already been done, the optimum timing is when the flag leaf is fully emerged, he believes. “There’s always a danger that you won’t get the most from the spray if you go too early. Timeliness and accuracy are essential at T2.”

He reminds growers that there should be no more than a month between the T1 and T2 sprays. “Aim for 21-28 days. It’s why we don’t want spray programmes to start too early – once you’re off, you have to keep going.”

The cooler end to March was a help in this respect, says Mr Stephenson. “It helped to dry up some of the disease present and meant we were looking at a good spray timetable, rather than a problematic one.”

Both men agree that the T2 spray should contain an SDHI, but that triazole choice and rate is important, too, following sensitivity shifts and reduced activity. Plans should be in place for at least a three-quarter rate of triazole.

“There’s more management flexibility with a product such as DuPont’s Vertisan, which allows you to choose the triazole partner and mix your own solution,” says Mr Stephenson. “It’s another choice this year.”

Mr Bean says there is good data on penthiopyrad, adding that 2014 is the first time many growers will have the opportunity to try it. “Don’t overlook it. It has done very well against brown rust.”

However, Aviator and Adexar are likely to be the leading T2 SDHI choices, they acknowledge. “But neither of these are foolproof. Both will potentially benefit from the addition of tebuconazole to broaden their activity against septoria and, in the case of Aviator, to enhance rust control,” says Mr Stephenson.

Mr Bean’s preference is for a mixed triazole at T2, such as Brutus or Prosaro, for its combined effect. “By having two complementary triazoles in the mix, you are covering more septoria strains and helping to protect the SDHI.”

He adds that prothioconazole and epoxiconazole are active on the same strains, while metconazole and tebuconazole will pick up most of the others.

That’s why it’s important not to mix the wrong ones, cautions Mr Stephenson. “Understand what you’re trying to do, which is to cover the greatest proportion of the population. Remember that cyproconazole has the same spectrum as epoxiconazole and prothioconazole.”

If the front part of the disease control programme has already contained epoxiconazole and prothioconazole, using either metconazole or tebuconazole as the mixing partner is sensible, he suggests.

While the SDHIs are effective on rust, adding a strobilurin – either azoxystrobin or pyraclostrobin – at T2 can help with bad infections, says Mr Bean. “Don’t forget that there’s an uplift in protein performance on milling wheats where a strobilurin is included.”

The final point is whether or not to add chlorothalonil. Mr Bean reports mixed trial results, but advises it can be added to Adexar, Imtrex or Vertisan for septoria. “Be careful where rust is concerned. There have been negative effects on both brown and yellow rust with a range of partner products.”

For Mr Stephenson, the advantages of adding chlorothalonil outweigh the disadvantages in a high-pressure septoria year.

“For the West and South West, it’s probably best to include it. In the East, make your decision on the day, depending on the pressure and how much you’ve already put on.”


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