Don’t panic about very big oilseed rape crops, but consider the use of a PGR-type fungicide if phoma control is still to be done.
Growers who have already treated for phoma should wait until the spring to bring canopies under control, says Pete Berry of ADAS.
“Autumn PGRs can help, but the biggest benefits come from spring applications,” he advises.
Although trial work shows that November and early December applications of metconazole will still reduce the size of the canopy, Dr Berry believes this is only relevant if phoma control is due.
“Both tebuconazole and metconazole will give you the disease control and some growth regulation.”
Independent agronomist Bridget Carroll in Lincolnshire sees little point in applying a growth regulator at this stage of the season.
“Get the crops through the winter and then make your decisions in the spring,” she says. “The fact that there’s very little phoma around has made the management of crops more straightforward.”
Lee Bennett of Openfield points out that root development stops once the canopy closes in. “That’s why a triazole is used at a very early stage in Germany, as they always get a hard winter.”
He says growers will only get a very limited effect from using metconazole now, and also suggests spring management. “If we have another cold winter, there will be some leaf kill.”
The lower pods make all the difference to yield, adds Mr Bennett. “In lush, thick crops, you don’t get the necessary lower branching. There’s always the option to take the top off knee-high crops, as that removes the luxury leaf.”