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Don’t court returns with low herbicide rates

Innovation Centres
Mel Wardle Defy seed rate return
Increasing the rate of Defy in a pre-emergence stack from 2.0 l/ha to 3.0 l/ha, reduced Black-grass seed return by an average 160 kg/ha - equivalent to the seed rate typically used to sow a lawn, reports Mel Wardle.

Increasing pre-emergence Defy application rate to 4.0 l/ha could reduce Black-grass seed returns by the same weight of grass seed per m2 as used to sow Wimbledon Centre Court.

Results of trials at Syngenta Black-grass Innovation Centres have consistently shown the increased control from a higher rate of Defy in the autumn pre-emergence herbicide stack, reported the company’s Cereal Herbicide Campaign Manager, Melanie Wardle.

“Increasing Defy rates from 2.0 l/ha to 3.0 l/ha reduced Black-grass seed return by an average 3200 seeds per m2 – an equivalent to 160 kg/ha,” she highlighted. Further increasing the rate, to 4.0 l/ha, gave another step change in improved control – reducing seed returns by more than 5800 Black-grass seeds per m2, or 290 kg/ha, compared to the 2.0 l/ha rate.

“Reduced rates of control not only hits yields of the growing crop, but the enormous seed return has long-term implications right through the rotation and the potential success of any future control strategies,” warned Mel. 

She pointed out that adding Defy into the pre-emergence stack had always improved overall efficacy and Black-grass control. “With the aim to achieve 97% Black-grass control just to hold populations in check, growers and agronomists need to maximise performance at every point in an integrated approach,” she added.

Black-grass heads above wheat

Additional products and higher rates will increase growers’ costs, she acknowledged. However, this season’s trials at the Syngenta Black-grass Innovation Centre in Cambridgeshire, for example, have demonstrated the damaging yield effects of Black-grass populations mean growers can see a positive financial return on Defy pre-em herbicide investment in the first year alone – along with the longer term implications of managing weed numbers more effectively as part of a long-term integrated control strategy.