HITTING the perniciouc weed, black-grass, hard by increasing a pre-emergence Defy application rate to 4 l/ha, could reduce its seed production by the same weight of grass seed per m2 as that used to sow Wimbledon Centre Court.

Results of trials at Syngenta’s Black-grass Innovation Centres consistently show that higher rates of Defy in autumn pre-emergence weed control give a reduced natural re-seeding rate of the weed the next year.

Its herbicide campaign manager, Melanie Wardle, said: “Increasing Defy rates from 2 l/ha to 3 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 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 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,” she warned.

“With the aim of achieving 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.

This season’s trials at it Cambridgeshire centre, demonstrated the damaging yield effects of black-grass populations – which means growers can see a positive financial return on Defy pre-em herbicide investment in the first year alone.