TACKLING BLACKGRASS as early as possible in the autumn is more effective than waiting until the spring and could reduce potential resistance build-up, experts have advised.

Growers must avoid adopting a ‘wait and see what emerges’ policy and should instead follow a pre-planned, or prophylactic, approach, suggested Rothamsted Research weed ecologist, John Cussans.

“You have to have effective control in place if there’s a history in that field. It’s not just about crop yield loss – it’s about how numbers increase through subsequent crops.”

Every 100 blackgrass heads per square metre left in the crop causes a 5% yield loss, he noted.

While this may not sound high, infestations of up to 450 heads per sq metre have been found in Syngenta trials, said the firm’s Iain Hamilton. In a 9t/ha wheat crop at £65/t this would be equivalent to over £130/ha in lost income.

“With these sort of losses at stake, the herbicide programmes growers choose mustn’t only do a good job, but must be cost-effective as well.”

Better herbicide timing is a key area for improvement. Spring removal can result in 16% less yield compared to autumn control, so an early, robust treatment is vital, he said.

Mr Hamilton suggests using Hawk (clodinafop-propargyl + trifluralin) – based mixtures while the weed is at its most vulnerable 1-2 leaf stage.

But any strategy must maintain the sustainability of currently-available products and growers should use herbicides with a different mode of action to those used last year, added Procam’s David Ellerton.

“If you wait until spring you are putting huge pressure on and likely to select for resistance.”