Crop Action Article - Managing Oilseed rape post-harvest

Oilseed rape seed leftover from harvest can easily become a persistent and competitive weed in the rotation. The plant only reproduces by seed but can become very competitive in subsequent cereal and spring crops as well as a key source of contamination by increased erucic acid content.

Whilst it is relatively easy to control in cereals with pendimethalin, diflufenican, flufenacet and ALS-inhibitors, it can be a difficult weed to control in a wide range of other broad-leaved crops as it germinates in both the spring and autumn.

The number of seeds that become dormant is very dependent on the timing of the first cultivation after harvest. Moving the shed seed into dry soil provides the ideal conditions darkness and water stress. Approximately 5% of dormant seeds will remain viable for between 3 and 15 years.

Cultivations should be delayed for 4 weeks after harvest especially when the soil is dry. Where the soil is moist, shallow cultivations (5cm) will keep the seed where it can germinate easily, and it can be sprayed off prior to drilling to reduce populations.

In situations where the burden of oilseed rape in the seedbank is known to be high, growing Clearfield® varieties which are tolerant to imidazolinone herbicides can offer a good control solution.