Canopy management in oilseed rape

Most solar-energy capture occurs in an open canopy, which allows light to penetrate down to the lower leaves. Use the crop’s green area index (GAI) to steer canopy management and maximise light interception.

Crops harvest energy and convert natural resources into biomass. Leaves, which have a greater photosynthetic rate than pods and stems, play a critical role. The crop’s green area index (GAI) can guide canopy management.

GAI is the ratio of green leaf and stem area to the area of ground on which the crop is growing. Calculate GAI by:

• Comparing the crop to reference photos
• Uploading crop photos to an online GAI tool
• Cutting all crop from a 1 m² area, measuring the fresh weight (in kg) and multiplying the weight by 0.8. This method is most appropriate where GAI is above 3

Nitrogen management has a significant effect on canopy development. The AHDB Nutrient management guide (RB209) provides information on nitrogen rates and timings.

If crops have a GAI greater than 1 at green bud (GS51) or 2 at yellow bud (GS59), then consider a plant growth regulator (PGR) application. A PGR will reduce lodging risk and increase seed set (as less light reflection is reflected from the flowers) and rooting below 40 cm. The optimal timing of a PGR application is between late green bud and mid-flowering, with earlier timing better for varieties associated with greater lodging risk. As several PGRs also have fungicidal activity, timing also needs to reflect the need to control diseases. Where canopy growth is suboptimal, consider fungicide products with no PGR activity. The optimum GAI at flowering (GS60) is 3.5.