Yellow rust shows no need for panic
By Mike Abram
Early season yellow rust infections have been found in susceptible wheat variety Robigus, despite expert pre-season predictions that the disease would not be an issue this year.
But the variety”s breeder, CPB Twyford, stresses infections will not explode overnight as in previous susceptible varieties Slepjner and Brigadier.
“There”s no need to panic,” says the firm”s agronomist Simon Francis. “As far as I am aware, infection is at low levels, and from our previous experience, I wouldn”t expect yellow rust to build up very quickly.
“It is not a Slepjner situation – you won”t have a yellow crop overnight.”
Three yellow rust Robigus infections have been reported around The Wash and in five fields in East Yorks, says Agrovista technical manager Mark Palmer. “There is no reason to believe there won”t be other cases.”
Further reports indicate yellow rust in the Borders region of Scotland, notes BASF”s Dick Dyason.
Infection this early in the season is a surprise, suggests independent consultant Bob Simons. “I”ll be adding my name to the list of experts who thought it wouldn”t be an issue, particularly this early.”
That”s because inoculum levels after last season were extremely low and because of the apparent tendency for yellow rust to develop quite slowly in the variety during early growth stages, he says. “I”m genuinely surprised – I thought it would only appear around flag leaf timing if growers had been a bit light on their T1 sprays.” Weather conditions have been perfect since last autumn for yellow rust development, says Mr Francis. “There is no need to panic – it is a management situation.”
But growers” fungicide strategies for Robigus may need refocusing, he adds. “Some might need to get away from a low-input mentality.”
Mr Simons agrees. “There were growers thinking of not spraying until flag leaf – this clearly indicates that wouldn”t be prudent.”
Instead, get out and inspect Robigus now, he advises. “Some growers may have relaxed after press reports suggesting rust wouldn”t be a problem and not looked as closely as they might have done.”
If rust is spotted, treat with a rust-active triazole at an appropriate dose, advises Hutchinson”s Dick Neale. “There is a range of triazoles that can be used – epoxiconazole would be good, but tebuconazole or cyproconazole are also very good.”
Timing will depend on whether a T1 is imminent, adds Mr Francis. “If T1 is going to be a couple of weeks away, it is common sense to clean up now with a low rate of triazole. But if T1 is only a week away, it should be OK to hang on.”
Strobilurins may also be back in contention at T1 on Robigus if the disease continues to develop, says Mr Neale.
“Pyraclostrobin and azoxystrobin are very active against rust, so growers may consider them for longer-term control.”
