Determination of risk-factors for the occurrence of Verticillium longisporum
In a two-year monitoring experiment the occurrence of Verticillium-wilt in oilseed rape could be confirmed for all surveyed regions in Germany. However, there are some regional differences in the infestation frequency. In north- and northeast-Germany, traditionally areas where oilseed rape production is highly-intensive, the disease was more frequently diagnosed. The data obtained from the determination of risk-factors showed a clear effect by the percentage of infected oilseed rape during crop rotation with V. longisporum. By extending the oilseed rape crop rotation to longer intervals (more than three years) and an additional growing of non-host plants in close cereal/oilseed rape crop rotations, the risk of an infestation by this pathogen could be lowered. In addition, a longer rotation period between oilseed rape crops had a positive effect on subsequent yield. However, the importance of conservation tillage systems as a risk-factor could only be basically confirmed and further investigations are still required. The same conclusions were reached with respect to differences in varietal susceptibility which recently became apparent. There was no effect associated with the application of organic nitrogenous fertilizer, soil type, pH-value and the application of fungicides on the occurence of Verticillium-wilt disease.