Be ready for weed control in oilseed rape

Date:02-03-2011

Despite the cold winter, several species of difficult and competitive broad-leaved weeds in winter oilseed rape such as sow-thistle, cleavers and crane’s-bill are present in crops and, as soon as the weather warms up, they will be ready and waiting to romp away and cause yield and harvesting problems. Stuart Jackson of Dow AgroSciences points out that these weeds will need checking before they become too big a management problem and that growers should make sure that they have sufficient herbicide in the store now to tackle the problem as soon as conditions allow.

"Every year there are some fields and some farms that have problem weeds such as sow-thistle, mayweeds, cleavers, and creeping thistle. Advisors know only too well from experience and farm history which fields are likely to warrant treatment. Some may want to have another look though as, with the tighter rotations and the changes in establishment, sow-thistles in particular appear to be much more widespread. These problem weeds compete directly with the crop and also smother the crop, making harvesting much more difficult and more costly, as many farmers will testify. Effective weed control is needed as soon as conditions allow."

Stuart points out however that there is a very limited choice of spring-applied herbicides for rape. "Galera, based on two active ingredients clopyralid and picloram, is the main spring applied herbicide for winter oilseed rape due to its level of performance and its weed spectrum."

"Galera works best when weeds are starting to grow and when temperatures are starting to rise. For sow-thistles you need much less active growth than, say for cleavers. Applied at 0.35 l/ha, it will give excellent control of mayweeds, creeping thistles, sow-thistle and very good suppression of cleavers. Groundsel is also well controlled up to the 6 leaf stage and good effects on cranes-bill have been reported," says Stuart.

"But its spray window is reasonably short, so farmers will need to make forward plans to get in sufficient herbicide stocks now, so that they are in a position to spray when they can. Galera can be applied from the 4 leaf stage of the crop up to the point just before flower buds are visible above the crop canopy – this cut off is usually at the end of March or beginning of April. Crop canopies have now opened up as a consequence of cold weather but once it starts to get warm and the first nitrogen is put on, both weeds and crop will start to grow away. Farmers plagued with these difficult weeds need to make sure that they have Galera in the store in readiness for optimum application timings, usually from mid-February onwards," explains Stuart.

Stuart Jackson reminds growers of their responsibility of keeping pesticides well away from water courses. "Extra care needs to be taken at time of spraying to avoid any contamination of water courses."