Strobilurins now useless on mildew
26 July 2001
Strobilurins now useless on mildew
By Andrew Swallow
FIELD trials have shown mildew control using strobilurins is a thing of the past, according to SAC Scottish Agronomys Huw Phillips.
He believes the findings strengthen the argument for a one-hit combined mildew and eyespot treatment.
In work near Dundee, Claire sown on 26 October last autumn was treated with 10 different fungicide programmes.
Wherever a strobilurin without a specific mildewicide was used at T1, mildew developed as if untreated.
“Our conclusion is that the strob activity on mildew is nil. It has gone completely,” said Mr Phillips.
Including a mildewicide in the T1 mix, or at T0 with the first growth regulator, is now essential on susceptible varieties, he added.
Quinoxyfen or a morpholine may do the job, but with nearly all wheat in Scotland also at risk from eyespot, cyprodinil (as in Unix) is a much better bet.
He recommends using a triazole, such as Opus (epoxiconazole), at T1 to clean up septoria and protect new growth.
Strobilurin applications can then be targeted at flag-leaf and the ear-spray where their longer protection will be of most benefit.
T3 applications particularly help maintain specific weight, Mr Phillips advises.
“On a 10t/ha crop the difference between 72kg/hl and 70kg/hl is worth 20/ha. At 68kg/hl it could be 60/ha, if the crop is not rejected.”
And it is a misconception that T3 strobilurins delay ripening, Mr Phillips added. “Some people have lost the plot a little in blaming the T3 for the green straw.
“The ear will ripen, it is the straw that hangs on and that has more to do with the T1 and T2 sprays.”