Cleavers in winter oilseed rape will cut down growers profits and make harvesting much more of a problem; so if you have had cleavers in the past or you can identify them in the field, now is the time to treat them, says David Roberts of Dow AgroSciences.

Cleavers are by far the most competitive broad-leaved weed in oilseed rape, with just 1 plant per square metre reducing yield by 5%. "That may not sound much but with rape at £350/tonne, a 5% loss of an average yielding crop is worth £61.50/ha – for just 1 weed/m². Cleavers will also reduce the final oil content of the crop, so it's a double whammy of less overall yield as well as substantial oil penalties. These weeds could cause a second double whammy at harvest time, with the mature plant clambering up and over the crop canopy, causing serious and costly harvesting problems, and its weed seeds contaminating the end sample leading to admixture penalties. You really can't live with cleavers in rape or indeed in other arable crops- they just remove profits," says David.

"Advisors usually know which fields are likely to warrant a herbicide treatment and the time for applying Galera, the one herbicide that will do a really good job on cleavers in winter oilseed rape, is approaching fast. For best performance, it is essential that Galera is applied when cleavers are actively growing and when temperatures are starting to rise, with air temperatures preferably 8ºC. Growers must be aware of the product’s cut off date however. Galera can be applied up to the point just before flower buds are visible above the crop canopy."

David points out that this year the cut off date for Galera in very early drilled rape could be mid to late March, whereas in later drilled ones the spray window could be open through to mid April. “Usually Galera is applied just prior to canopy closure during a period of active weed growth.”

"This is typically one week after the first Nitrogen application, but with some crops too advanced to warrant early nutrition, then advisors should use the crop growth stage as the cut-off criteria."

Another issue at this time of year can be wet leaves. Galera needs 6 hours drying time after application to a dry leaf for best results. A breeze to dry the plants off in the morning and a planned application during the warmest part of the day is the approach most likely to give good results.

Applied at 0.35 l/ha, Galera will give very good suppression of cleavers, up to 85% as well as excellent control of mayweeds, creeping thistles, sow-thistle. With regard to weed size, it controls cleavers and mayweeds up to 150 mm in size, sow-thistles and creeping thistles up to 4 leaves or 50 mm in size and groundsel up to 6 leaves.

"Controlling cleavers in winter oilseed rape to such a level will minimise any seed return and help reduce spend and improve margins in following any crops," says David.

Galera (267 g/L of clopyralid and 67 g/L of picloram formulated as a suspension concentrate) is recommended post-emergence in all varieties of winter oilseed rape for the control of broad-leaved weeds including cleavers, mayweed, sow-thistles and thistles.  It can be applied from the 4 leaf stage of the crop up until before flower buds are visible above the crop canopy.  As with most herbicides, do not apply to stressed crops - due to nutrient deficiency, frost damage, phytotoxicity from previous agrochemical applications, cold soil (roots) and warm air (stem/foliage), water logging, rapid fluctuations in air temperature, mineral deficiencies, disease, plant injury e.g. pigeons. It is recommended at a dose rate of 0.35 l/ha and is compatible with a wide range of graminicides, insecticides and fungicides.  It is packed in a 1 litre container.