Wheat growers target septoria as T2 approaches

The same principles apply for flag leaf sprays this year, agree advisers. But rising fungicide costs are prompting cereal growers to look closely at spray programmes.

Septoria tritici will be the number-one target at T2, although widespread varietal susceptibility means that brown rust will almost certainly be a feature in 2009, says Bill Clark, director of Broom’s Barn.

“There are few varieties out there which aren’t affected by brown rust. Despite the conjecture, the cold winter hasn’t stopped it and there is inoculum around.”

As far as septoria is concerned, inoculum is never limiting, he adds. “As is the case so far this spring, disease levels are often low in April. But that situation changes very rapidly with the right conditions.”

Mr Clark’s advice to growers starting to plan their T2 applications is to judge the disease risk and treat crops accordingly. “Working to a set fungicide budget is a bad way of doing things, especially this year. You won’t get the best from your crops.”

Growers will be spending about £80/ha in total on fungicides in winter wheat this season, he calculates. “They can expect a 20% yield increase from a robust programme. At this level of response, the question to ask is why wouldn’t you make good use of fungicides?

“It’s true that fungicide prices have increased, but this shouldn’t affect your thinking too much.”

The triazole resistance debate is relevant, too, he notes. “It may have stabilised, but the concern is that the shift in sensitivity occurred while people were using less triazole. The loss of efficacy and the use of lower doses were a double whammy.”

In general, growers aren’t using enough, even though rates have risen recently, he warns. “You need higher triazole dose rates than you would imagine. Err on the high side of caution.”


Watch out for brown rust at T2, even though winter conditions appear to have been against it, warns Bill Clark

In practice, this often means three-quarter rate at T2, but survey results suggest that many growers are still using less than half rates, reports Mr Clark.

“Once the triazole choice and rate is agreed, remember that there’s still a place for strobilurins at the flag-leaf timing. They could be very important in bad brown rust areas,” he advises.

Although there may have been good reasons to use a strobilurin on backwards crops at T1 this year, Mr Clark’s preference is to save them for T2 and T3.

His final point is on spray timing. “Growth was slow to get going this spring, but the flag leaf spray will still be required on or around May 20. Don’t let your timeliness slip.”

Independent agronomist Steve Cook of Hampshire Arable Systems agrees that growers shouldn’t be looking to cut back on fungicides at T2, but suggests that there may be opportunities to employ cheaper options this season.

“If the T1 spray was well-timed, growers shouldn’t be chasing disease at T2. That gives them more choices, but it doesn’t do away with the need for robust programmes.”

Some of the co-formulation products are very well priced this year, he notes, adding that growers are likely to be coming back into crops with the T3 spray just two to three weeks later. “In this situation, the temptation will be to cut back a bit at T2. It’s a risky strategy and will depend on what was done at T1.”

Chris Rigley of Yorkshire Arable Marketing intends to base T2 sprays on a good rate of triazole for kick-back, as well as a reduced rate strobilurin. But he will be making tweaks to this base programme according to conditions.

“The strobilurin element will depend on variety. Robigus needs one for its ability to control rust, others for its physiological benefit.”

His other aim with the T2 spray is to make the best use of nutrition to keep the crop green. “We’ll be using a phosphite material, which enhances root action, and trace elements to help crops make the best use of nitrogen. Growers are looking to claw back some of the high fertiliser cost.”

Brutus good, but expensive?

New BASF fungicide Brutus (metconazole + epoxiconazole) has a role in a very eradicant situation at T2. But its price tag is a deterrent, agree most independent agronomists.
Steve Baldock of Prime Agriculture says there are strong technical benefits from using Brutus at both T2 and T3, but he considers it to be a very expensive choice. “There’s no doubting what it can do, the issue is whether growers are prepared to pay for that.”
His clients will be spending an average of £82/ha on fungicides this year, with about £32/ha going on the T2 spray. “That’s virtually 40% of the total spend. So it’s difficult to increase that without affecting other parts of the programme.”
Strobilurins will feature at T2 and T3 in his recommendations, he adds. “Their late-season effects on brown rust control and greening are worthwhile benefits. Using them at these timings will account for about £11.50 of the total spend.”
Mr Cook is also surprised by the price of Brutus. “But we might see some adjustment in the price of a number of products, especially if things didn’t move out of stores at T1 as expected.”
He predicts that there will be greater fusarium pressure due to the high levels of mycotoxins in last year’s crops, putting greater emphasis on the T3 spray than usual.
“It’s another reason why growers might think about cutting back at T2. The lateness of crops, prices of fungicides and lack of disease pressure are making people think twice.”

T2 sprays

  • Septoria remains priority
  • Watch out for brown rust
  • Place for strobilurins
  • Robust rates required
  • Brutus option, but expensive?

Prothiaconazole least affected by septoria mutations

Resistance testing on azole fungicides suggests that prothioconazole is the least affected by the different mutations picked up in the septoria fungus in laboratory testing, writes Mike Abram.
Several different mutations have been picked up through molecular analysis of septoria samples, with one, I381V, in particular, provoking interest from researchers.
Tests appear to show that isolates carrying I381V were more sensitive to prochloraz, which provoked suggestions the active might be useful in sensitising populations to other azole fungicides.
But the practical relevance of that discovery is still to be validated, Andreas Mehl, resistance expert for Bayer CropScience believes.
In his testing prothioconazole has been the least affected by the different mutations – ie no resistance has been detected. Other azole fungicides, such as tebuconazole have shown a much greater degree of resistance to some of the mutations.

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