Advanced rape crops need manipulation

GROWTH of forward oilseed rape crops must be steadied to reduce the risk of lodging, say agronomists.

After good drilling conditions and establishment, many winter oilseed rape crops have come through the winter with minimal outer leaf loss. Most crops are much more advanced this spring than they were the same time the last two springs.

Because final yield depends on an optimum sized canopy during flowering, early spring growth must be steadied, said independent consultant Ruth East.

“Creating an optimum sized canopy at flowering involves managing nutrition carefully and applying sufficient plant growth regulator. Too big a crop canopy at flowering means too little light penetration, lower rates of photosynthesis and subsequent lower yields. Larger crop canopies also create a microclimate for disease.”

Regular crop monitoring can be made easier by the use of a Green Area Index (GAI) tool on the web site www.totaloilseedcare.co.uk.

Growers can obtain an automatic GAI score for their oilseed rape by uploading a digital photograph of their crop to the website. From this information growers can make a decision on when and how much fertiliser and growth promoter to use.

“It’s no good doing it just the once, you should be monitoring crops throughout February for nutrition and in March and April for metconazole.”

It was already evident that many crops would require less nitrogen this year, suggested Ms East.

“Generally big canopies require less nitrogen, whereas smaller crops need more to get them going. Nitrogen should be applied when soil temperatures are above 4°C and once crops start to sit up.”

Rape crops with at least six true leaves and a GAI above one in March or two in April would benefit from the application of full rate metconazole. “Anything smaller and there is no need for a PGR.”

Full rate SunOrg Pro (0.8 l/ha) applied at stem extension to green bud would reduce stem height, control lodging and promote even flowering.