Plant vigour is key to weed threat

Plant vigour between drilling and late autumn is crucial to the overall density and weed competitiveness of oilseed rape crops this spring, according to latest research.

Trials at Rothamsted Research found a close correlation between ‘rape early vigour’ (measured in grams dry weight/ sq metre in December) and percentage yield loss from weeds, explained researcher, Peter Lutman.

“Very low plant populations from low seed rates [e.g. 2-3kg/ha] can produce strong growth from early plantings, resulting in good crop vigour and cover by early winter.

“However, crop vigour tends to be stronger with higher seed rates. Lower seed rates can result in plants with less vigour, particularly when planted later than the optimum time of mid to late August.”

Results showed that once dry weight vigour drops below 70 grams/m2, yield loss from 100 weeds/m2 will be around 10%. But, when dry weight falls to 40 grams/m2, the same weed density can produce yield losses of 40%, he said.

Cleavers are thought to be the most competitive weed in winter oilseed rape, followed by chickweed, sow thistle and mayweeds.