Cleaver control required sooner rather than later

Cleavers remain one of the most competitive weeds in oilseed rape and their effective removal relies on the timely use of pre-emergence residual-acting herbicides, particularly those containing quinmerac. BASF are urging growers to plan ahead this year and make sure that they control Cleavers in their winter oilseed rape now rather than later.

"Cleavers are so competitive, with just ten plants per square metre causing losses of over £250/ha. They are also a major nuisance at harvest, wrapping around and tangling the combine, leading to increased harvesting and labour costs. Their prolific seed production not only causes problems in following crops, but can also contaminate the seed sample at harvest, increasing drying costs and even leading to crop rejection," says Diane Heath, BASF Oilseed Rape Product Manager.

She points out however that oilseed rape growers don't have a lot of choice when it comes to Cleaver control. "One thing for sure is that 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. Later post-emergence options leave growers exposed to unreliable results; the real choice comes down to one of three herbicides containing metazachlor and quinmerac - Katamaran, Novall or, new for this year, Oryx."

"It is quite understandable that growers are keen to harvest the crop and move onto planting the next crop, but Cleavers will cost them dear unless appropriate and timely measures are taken now."

"Early control must be a priority, particularly where high weed pressure is expected, crop emergence is delayed or where low seed rates are used."

"Also there are more spraying opportunities at this time of year than for the later post-emergence herbicides, which means that growers can rely on accurate and timely control measures. In September for example you have twice as many suitable spray days as there are in November and three times as many as in December."

According to Diane, "Weed control in oilseed rape should start with an appropriate dose of a residual pre-emergence herbicide; lowering dose rates will compromise the effectiveness on priority weeds such as Cleavers and Poppy."

She advises that it is vital to keep the rate of quinmerac up to the optimum level of 250 grams per hectare for Cleaver control. "For Katamaran this means keeping to 2 litres/hectare, for Novall 2.5 litres/ha and for Oryx 3 litres/hectare. Quinmerac adds a number of additional weed benefits to metazachlor (as Butisan S). In 21 trials Katamaran at 2 l/ha gave 95% control of Cleavers compared with 62% resulting from 1.5 l/ha (750 grams per hectare) of metazachlor. For Poppy in 14 trials Katamaran gave 90% control compared to metazachlor's 69% and in 7 further trials Katamaran gave 90% control of Field Speedwell compared to 72% for metazachlor."

"The effect of quinmerac in the co-formulated herbicides was even more pronounced under high weed pressure. In a trial that had over 51% ground cover of Cleavers in the untreated, metazachlor struggled to give 13% control but Katamaran gave an amazing 99%."

"Cleavers are a problem that need to be considered right across the whole arable rotation, as the effectiveness of this Autumns treatment will have major implications on next years rape harvest and next years following crop. The impact on yield and costs of a Cleaver infestation appears to be getting more significant with the trend towards smaller canopies and the increased popularity of direct combining. So although it is difficult to think about using a Cleaver-active pre-emergence herbicide before you can even see the weed, growers can be assured that what they do now will reap financial benefits in the long run," concludes Diane.