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Time for pre-em applications

Agronomy Issues
08.09.2018
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Pre-emergence herbicides have consistently helped boost performance of the post-em stack, according to results of Syngenta grass weed specialists' trials across a range of establishment techniques.

Pre-emergence herbicides should be applied within 48 hours of drilling, irrespective of the products chosen in the stack, advises Syngenta grass weed specialist, James Southgate.

Trials at the Syngenta Black-grass Focus Site, in Cambridgeshire, have shown pre-em applications provide consistently more reliable grass-weed control, compared to peri-em treatments as the crop emerges, he reported.

”Results with peri-em trials highlighted the difficultly of assuring precise timing, with potential issues of rain and wet conditions giving a greater margin for error" he said.

With a solid pre-emergence stack in place, James pointed out a sequenced post-emergence treatment was able to deliver the best results, typically adding over 15% extra black-grass control in the Barton trials.

James Southgate

“In high black-grass populations, sequencing of actives improved results in all establishment techniques, even after stacked pre-emergence,” he advocated, “with the biggest gains for direct drilled crops.”  

Read more on the implications of establishment technique for grass weed control

Herbicide stacking

The Barton research has reinforced the understanding that increasing the number of active ingredients in a pre-emergence stack delivers consistently increased control. In a summary of 26 trials, James highlighted that the step from four to five actives in the pre-em mix achieved just as big a step change in control as the move from two to three actives.

“It’s not a law of diminishing returns, but consistently increasing results,” he pointed out. “Across all the trials, only the five active mix was able to produce an average rate of control over 90%.”

Furthermore, extensive trials have shown that increasing the rate of Defy in the pre-em mix further progressively increase the level of black-grass control. Increasing the rate in a mix from 2.0 l/ha to 3.0 l/ha increased control by 6%, but a move to 4.0 l/ha added a further 5% of control efficacy.

Achieving the highest level of control with Defy at 4.0 l/ha, compared to using 2.0 l/ha, would equate to over 5800 less black-grass seeds being returned at the end of the season.