Which triazole remains a tricky choice for T2 spray

Heavy recent rain in many areas has sparked reminders of the importance of wheat flag leaf (T2) fungicide treatments.

Controlling septoria remains the main aim, but rusts, mildew and tan spot are all potential yield-wreckers if crops are inadequately protected at this looming key spraying point.

“T1 timings have been all over the place,” says ProCam’s Dave Ellerton who advises that the interval between T1 and T2 should not exceed four weeks.

Scottish Agronomy’s Allen Scobie agrees.

“Anyone who left a five- to six-week gap last year will not forget the damage it caused.”

Although the septoria threat is likely to be lower than usual, partly because of rapid recent growth, it is sensible to check, says ADAS’s Bill Clark.

“If there is any sign of septoria on leaf three then the crop is at high risk, no matter what variety, location or recent weather.”

The main question for growers is which triazole to use.

“The myriad mixtures of triazoles and stacked products like Prosaro and Cherokee make product choice and dose decisions difficult.”

For all high risk varieties and for moderately susceptible ones in the west and south-west growers should select the best against septoria, he advises.

“That means Opus and Proline.”

More resistant varieties – Alchemy, Brompton, Claire, Deben, Gatsby, Glasgow and Robigus – allow savings to be made, either in dose or through cheaper triazoles, he explains.

Prothioconazole (in Proline) is a good alternative to epoxiconazole (as in Opus), but not as curative on septoria or yellow rust and is weak on brown rust, notes Mr Ellerton.
That can be overcome by adding a rust-effective active such as cyproconazole or tebuconazole (as in Prosaro), he says.
After 30mm of rain over the weekend don’t stint on triazole doses, urges Hutchinsons’ Dick Neale. “The crop potential’s there, but the disease pressure’s also enhanced, so you need at least three-quarter doses.”
Chlorothalonil is seen as a valuable protective component in T2 mixes.
“It has a useful role to play at this timing, so don’t miss it out,” says Mr Scobie.
“It’s got to go in,” agrees Mr Neale. Mr Clark regards it as “still a good buy at GS39”.
Despite widespread septoria resistance to them, strobilurins, particularly pyraclostrobin given this season’s price cut (see p62), still have a place at T2.
Mr Scobie has reservations. “The average yield response to strobilurins is very small, so you need to buy your strob well to get a return.”
But Mr Clark would include one even if rust was not an issue. “Half dose strob at flag is still, on average, likely to give a profitable yield response.”
Pyraclostrobin, which gave responses of up to 0.7t/ha last year in Hutchinsons’ field scale trials is particularly good value, notes Mr Neale.
With its extended label clearance this season (up to GS51) Tracker (boscalid + epoxiconazole) is another good fit at T2, especially in crops carrying high levels of eyespot, he adds.
andrew.blake@rbi.co.uk