Cleavers control in heavy land rape is best post emergence

UK - March 20, 2006

Heavy land winter oilseed rape growers are relying on late post-emergence herbicides for cleavers control because of the risk of using pre- or early post-emergence herbicides.

“Early autumn control of cleavers in winter rape on heavy land is not an option because of the high possibility of redrilling,” says AgroVista’s Andrew Mellors.  Many of his clients farm very heavy clays on marshland near the Lincolnshire coast.   

“Producing a fine, firm and even tilth on these heavy clay soils for winter rape drilling is notoriously difficult, even with minimal tillage.  Seedbeds are often cloddy, uneven creating conditions that can lead to poor establishment and, even redrilling.   

“Risks can be compounded if subsequent weather conditions lead to crop damage or indifferent weed control.  If early treatments have been applied, herbicide residues can limit redrilling options,” explains Mr Mellors.   

He advises growers to rely on post-emergence herbicides for grass and broadleaved weed control once the crop is well established.   

Ross Hewson, who farms near Grimsby, uses propyzamide in late autumn for grass and broadleaved weed control.  This leaves a moderate mayweed population with a few sow-thistles and a guaranteed population of cleavers across most fields. 

Mr Mellors recommended Galera (clopyralid + picloram) to control the cleavers, sow thistles and mayweed as soon as it was launched three years ago.  The herbicide is applied once the oilseed rape is responding to the first nitrogen top dressing and cleavers are starting to move strongly usually during the last week of March.   

Crop safety is not an issue, and where appropriate, Mr Hewson has had no problems tank mixing Galera with a fungicide or insecticide. 

“At 0.35 l/ha we consistently achieve 90% plus control or strong suppression of the cleavers using Galera, and total control of other weeds.  Where cleavers are suppressed but not actually killed, they are so weak that they fail to produce any significant numbers of viable seed.  They just remain weakened and stunted in the bottom of the crop,” says Mr Hewson.