Cultural control of volunteer oilseed rape (Brassica napus)

Laboratory studies on the biology of oilseed rape (Brassica napus L.) showed that the induction of secondary dormancy is influenced by light environment, time of exposure to light and darkness, temperature regime and genotype. Seeds did not become dormant while exposed to light but were increasingly likely to become dormant the longer they were exposed to water stress and darkness. Dormancy was broken by alternating warm and cold temperatures. Conclusions from results obtained in Petri dishes have been tested in the field and hypotheses regarding the effects of post-harvest cultivation have been proposed. In July 1995, field experiments were initiated on a flinty silty clay loam and a sand to test the implications of post-harvest cultivation on the development of a persistent seedbank. The results largely confirmed assumptions made on the basis of laboratory findings. Seeds that had been exposed to water stress and darkness for longest, by cultivating the soil at the beginning of the experiment, immediately after seed distribution, exhibited the highest persistence rates. Seeds that were exposed to light for 4 weeks and then incorporated into the soil built up a much smaller seedbank. The seedbank was very small or nonexistent in plots that had not been cultivated at all.