8 June 2001

Act promptly to stop sun scorch in spring barley

APPLY spring barley fungicides to prevent ramularia and physiological spotting before symptoms are seen, advises the SAC.

"As soon as the ear is out the spots just come in, almost as if it is a growth stage trigger," says senior cereal pathologist Simon Oxley. "The optimum time to spray is on to a pristine crop at the boot stage."

Forward crops in Scotland and Northumberland – areas which have been hammered by the phenomenon before – are almost at that stage now. "Waiting for ear fully emerged could be too late to prevent yield loss," says Dr Oxley.

A strobilurin fungicide seems to be the key to control. "It does not matter whether it is Amistar, Twist or the Opus co-formulation Landmark, but it should always be in a mixture with a fungicide with another mode of action."

Epoxiconazole has proved a good partner product, but Punch C (carbendazim + flusilazole) is not, says Dr Oxley. Chlorothalonil offers an effective cheap alternative, provided the formulation is approved for use on barley – but Bravo is not, he warns.

All spring barley crops in at-risk areas warrant a second fungicide, believes Dr Oxley, but severity of spotting and response to treatment does vary by variety. Chariot is most severely hit.

"Yield responses can be up to 1t/ha." Typically a 40% dose of strobilurin plus 40% dose of partner product should be sufficient, he says. &#42

Not just in north

There is some evidence that the spotting phenomenon, be it ramularia or sun-induced physiological spotting, is not limited to the north and Scotland. "I know that the Morley Research Centre in Norfolk had a lot of physiological spotting in Chariot two years ago," says Dr Oxley. Crops in Ireland and Germany, at similar latitude to central England have also been hit. Wet or showery weather followed by intense sunshine seems to be the common factor, he says.