Sow-thistles could rival cleavers as the major weed threat to some oilseed rape crops this season, Dow AgroSciences has advised growers.

Ideal weather and soil conditions last summer/ autumn led to good wind dispersal, together with successful seed germination and survival, the firm said.

“An increased use of minimal tillage methods to establish winter oilseed rape, combined with very dry and warm conditions after harvest, has led to sow-thistle populations soaring,” said technical specialist, Rene Pollak.

One plant can shed over 20,000 seeds, so growers should not underestimate the potential impact on yield, harvesting difficulties and increased grain moisture content, he said.

“Populations of above three plants/ m2 are worth treating. Figures show that five sow-thistles/m2 can cost the grower over £40/ha in lost yield on a 4.3t/ha crop.”

Mr Pollak suggests applying Galera (clopyralid + picloram) at 0.35litres/ha when target weeds are showing new spring growth and at a crop stage up to and before flower buds are visible above the canopy.