Cleavers are so competitive and difficult to control that early control in oilseed rape is the only sound strategy to adopt. Leaving weed control until the spring allows this highly competitive weed to erode yield and get a hold of the crop when it is at its most vulnerable in the autumn, according to BASF and independent agronomists.
"Cleavers in oilseed rape are widespread and competitive, with just ten plants per m² causing losses of over £250/ha. They are prolific seed producers and left uncontrolled will compound the problem in the following crop, which is most likely to be a first wheat. Cleavers cause both practical and financial problems at harvest, making harvesting difficult and drying and storage expensive. Their control in the early autumn is essential and benefits both this year's and next year's crop, potentially reducing herbicide costs across the rotation," says Diane Heath, BASF Oilseed Rape Product Manager.
Arable consultant and AICC member, Steve Harrison indicates that sometimes farmers are too keen to harvest the current crop and then plant the following crop, rather than look at the additional costs they may have to pay at the following harvest if early measures to control Cleavers were not taken. MORE….
"Cleavers will interfere with harvest, wrapping around and tangling in the combine and their presence at harvest will increase costs and time. Cleavers can also substantially increase drying costs. Oilseed rape was coming in at between 9-12% moisture this year and in some instances needed careful drying. Cleaver seed at harvest is still green and immature with much higher moisture content of around 40% and their presence in admixture will increase drying time, thereby increasing overall costs."
According to Steve, "Weed control in rape starts with an appropriate dose of a residual pre-emergence herbicide, and if Cleavers are particularly bad, Katamaran or Novall, both of which contain metazachlor and quinmerac in differing ratios, would be used. Where Cleavers are a problem, the dose rate of the product should be kept up. For Novall I recommend it at 2.5 l/ha. This delivers 1000 g/ha of metazachlor (equivalent to 2.0 l/ha of Butisan S) and 250 g/ha of quinmerac. For Katamaran the rate should be 2 l/ha."
"Late post-emergence treatments are available now but are Cleaver-suppressors only. They are not as effective or as reliable as the pre-emergence options. Looking at the Cleaver problem across the arable rotation, it is important not to forget the implications of your actions now on next years harvest. What may be seen as a questionable investment at the start of the season, especially as you can't see the weeds you are intending to control, will reap considerable financial benefits at harvest," concludes Steve.
