Leaf spot risk to OSR

OILSEED RAPE crops in many areas are at greater risk from light leaf spot this autumn, compared to last year, according to a Rothamsted Research forecast.

Scotland and the north of England are at greatest risk, while East Anglia is likely to suffer least, said Rothamsted’s Bruce Fitt.

Growers in high risk areas should consider an autumn spray, but he advises not apply it yet, especially if there is a risk of phoma stem canker.

“We anticipate the first phoma leaf spots later this month, and the optimum strategy where both diseases pose a risk would be to apply one spray against both diseases, after the phoma leaf spots have appeared.

“Growers in areas at risk from phoma should be inspecting their crops for leaf spotting.”

DuPont’s Andy Selley said that while the risk to crops in East Anglia is lower than further north, one in ten crops are at risk of having more than 25% of plants infected and growers should not ignore this threat.

“Light leaf spot can cost 1.5t/ha in yield. Growers should monitor [crops] using the plastic bag incubation technique to find out if there is any infection, and use a combined phoma/light leaf spot product such as Punch C [carbendazim + flusilazole] if necessary.”

With LLS treatments likely to coincide with a second autumn spray for phoma, it is important to maintain the rate for phoma, he said.

The Rothamsted national light leaf spot forecast can be found at http://www3.res.bbsrc.ac.uk/leafspot/