Producers in the Willamette Valley of Oregon are interested in growing canola as a rotational crop in grass seed and cereal rotations. Many other Brassicaceae seed crops also are produced within the valley. Concerns of seed persistence and volunteer contamination of Brassicaceae seed crops prompted the investigation of seed persistence and dormancy. Brassicaceae crop production can result in substantial input of crop seeds into the soil seed bank. These seeds may enter secondary dormancy, a condition which develops in mature dispersed seed, and form a persistent seed bank. Laboratory, greenhouse, and field studies were conducted over 4 years to determine if seed persistence of canola was different from that of other Brassicaceae crops produced in the valley. Surveys of seed loss were conducted during harvest. Canola seed loss was not different from daikon radish, turnip, or forage rape. In depth of emergence studies, canola and turnip seed emergence were similar; daikon radish emerged from greater depths. In field tillage trials, radish seedling emergence was greater than canola or turnip in deep tillage treatments. Seed persistence was not affected by crop type, but tillage treatments were significant. There were no seeds remaining in the no-till treatment after 38 months. The greatest number of seeds were recovered from the deep tillage treatment.
The viability of radish seeds buried in pods declined at a steady rate over 30 months regardless of burial depth. However, the total number of persistent seeds was greater at deeper depths. Incubation of seeds in polyethylene glycol (PEG) resulted in a broad range (0-20% in 2016 and 0-60% in 2017) of secondary dormancy induction. Canola and daikon radish have similar potentials for secondary dormancy induction and very few (<3%) turnip seeds were induced into secondary dormancy. Kale, collard, and Michihili Chinese cabbage had similar secondary dormancy potentials as canola in 2016. No seeds of Crimson Giant radish were induced into secondary dormancy. A relationship between temperature during seed production and dormancy potential was found. Seeds produced in 2017, which was cooler than average, had greater levels of secondary dormancy. NCED gene expression in osmotically stressed seeds was similar among species. Differences in relative expression and secondary dormancy induction indicated that NCED expression alone cannot predict dormancy potential. Studies were conducted evaluating the effect of 2,4-D and MCPA applications and timings on seed germination and root and stem growth. Applications of 2,4-D and MCPA in greenhouse studies resulted in reductions in canola root and stem growth. When applied pre-emergence, 2,4-D and MCPA reduced canola emergence by 45% and 60%, respectively, compared to untreated controls. In a field trial, 2,4-D reduced emergence of Brassicaceae seedlings by more than 90% when rainfall occurred within 1 wk of application. Canola did not persist to a greater extent than any of the other Brassicaceae crops with which it was compared. The secondary dormancy induction potential of canola was similar to that of other Brassicaceae crops which are produced in the Willamette Valley.