Two new soil pathogens, Olpidium and Pyrenchaeta, confirm that tighter oilseed rape rotations will create greater disease management problems.
Speaking at the Cereals Event in Lincolnshire, NIAB-TAG’s Ron Stobart confirmed that both pathogens, never before seen in oilseed rape, were found in trials where oilseed rape is grown in 1:2, 1:3 and even 1:4 rotations.
With oilseed rape prices at such high levels, its not surprising that farmers are attempting to maximise their rotational margin, but at what point does this become too costly was the question discussed.
A recently completed 8-year HGCA project reveals a 0.5t/ha yield penalty from tighter oilseed rape rotations, which Mr Stobart attributes to disease and volunteer problems.
The three questions to ask about oilseed rape, said Mr Stobart, are what rotation is best for yield, what’s best for gross margin and what is best to control weeds?
“At today’s prices a tight rotation of one in two or three years is very profitable, but it is not sustainable long-term,” he warns. The two new pathogens, as well as existing clubroot and verticillium wilt threats will only push management costs up if oilseed rape is grown in tight rotations long term.”