Oilseed rape disease levels below average in 2005

Disease levels in commercial crops increased in 2005 but were lower than the long-term average.

Although incidence of light leaf spot on the pods and stems was higher than in 2004, levels remained markedly lower than the 10 year mean. Previous season incidence is the main indicator of light leaf spot risk in the following season and disease levels this year suggest that there is an increased risk of light leaf spot in 2006 compared to this year. As usual the highest risk of light leaf spot will be in the north.

Phoma canker incidence was also higher than last season, although again markedly lower than the 10 year mean. The previous season's incidence of phoma is also a good indicator of risk for the following season. Disease levels this year suggest that there is an increased risk to crops from phoma next season, compared to this year. The distribution of stem symptoms in 2005 (cankers and stem lesions) was similar to last season; the majority of crops affected had a low proportion of stems showing symptoms. This was in contrast to 2003, when the largest proportion of crops had a high incidence of infection.

Timely autumn sprays should be a priority in the coming season, to minimise the risk from both light leaf spot and phoma canker later in the season.

Distribution of incidence within crops of plants showing phoma stem symptoms

National disease levels at pod development in commercially grown crops.