05-02-2014 01:01 AM | News

Prepare for a tight spray window for weed control



This will be a challenging spring to apply herbicides post-emergence in winter oilseed rape, but growers can make a judgement now of how much herbicide is needed this year and prepare ahead by ordering it forward and getting it into stores prior to application.

“Winter oilseed rape crops romped away in the autumn and much land is saturated. If you want to control difficult and competitive broad-leaved weeds in winter oilseed rape such as cleavers, sow-thistle and mayweeds , you need to be ready and waiting for both weeds and crops to grow away when the weather warms up,” says David Roberts of Dow AgroSciences.

He points out that these weeds need checking before they become too big a problem and growers should make sure that they have sufficient herbicide in store now to tackle the problem as soon as conditions abate.

“Cleavers are the most aggressive weed when it comes to competitiveness, impacting yield and decreasing percentage oil content. They can also lead to seed contamination which will mean an increase in admixture and a reduction in price/tonne. Controlling this weed in oilseed rape makes sense as it will mean no seed return, helping to reduce spend in following crops.”


“Every year some fields on some farms will have problem weeds such as cleavers, sow-thistle, mayweeds and creeping thistle that need tackling in the spring. Most advisors know from experience and farm history which fields these are likely to be. As well as being very visible at flowering, these problem weeds compete directly and smother the crop, making harvesting much more difficult and more costly. Effective weed control is needed, despite the difficulties that current wet conditions may bring,” says David.

“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. But its spray window is quite narrow. 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 is recommended 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, but with advanced crops this may be earlier.”

David advises that when the first nitrogen is applied and the weather warms up a bit, both weeds and crop will start to grow away. “Some crops could be near to the cut-off stage for Galera quite quickly. Farmers plagued with these difficult weeds such as cleavers need to make sure that they have Galera in the store in readiness for application, normally around one week after the first nitrogen is applied. Then both crop and weeds will be starting to grow,” explains David.

“Applied at 0.35 l/ha, Galera will give excellent control of cleavers, mayweeds, creeping thistles and sow-thistle. To get the best results on cleavers, conditions will need to be warm before and after application and the weed less than 150 mm. Groundsel is also well controlled up to the 6 leaf stage.”

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, especially when ground is close to saturation.”

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