The challenging autumn that offered little opportunity for pre-em herbicide applications and subsequent difficult establishment has led to many backward winter oilseed rape crops that are struggling to compete with the extra burden of broad-leaved weeds such as cleavers and cranes bill. But with the healthy price of oilseed rape, the majority of growers will be making sure that they manage their rape crops as carefully as possible this spring as this is the only way to better yields and profitability.
Several species of difficult and competitive broad-leaved weeds in winter oilseed rape such as sow-thistle, cleavers, mayweeds and cranes-bill are already 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. David Roberts of Dow AgroSciences points out that these weeds will need checking before they become too big a problem and growers should make sure that they have sufficient herbicide in the store now to tackle the problem as soon as conditions allow.
Every year some fields on some farms have problem weeds such as cleavers, sow-thistle, mayweeds and creeping thistle that need tacking in the spring. Most advisors know from experience and farm history which fields are likely to warrant treatment. But where a metazachlor based product was not applied this autumn, I would think that more advisors may want to try to recover their position on weed control this spring and consider whole farm applications. As well as being very visible at flowering, problem weeds including cleavers, sow-thistle, mayweeds and creeping thistle compete directly and smother the crop, making harvesting much more difficult and more costly. Effective weed control is needed as soon as conditions allow.
David points out that there are few spring-applied herbicides for winter oilseed rape. Galera, based on clopyralid and picloram, is the main spring applied herbicide for winter oilseed rape due to its level of performance and its weed spectrum. It works best when weeds start to grow and when temperatures are starting to rise. For sow-thistles you need much less active growth than you do 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.
But its spray window is quite narrow, so farmers need to get sufficient herbicide onto the farm ahead of the game, 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. Most rape crops are less developed than normal this year, but once the first nitrogen is applied and the weather warms up a bit, 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 application applied around one week after the first nitrogen is applied. Then both crop and weeds will be starting to grow and there is a good compromise between weed shading and crop competition, explains David.
David Roberts 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.