High dormancy levels in freshly shed black-grass seeds have led to particularly prolonged germination this year.
With early drilled crops up and away this autumn, pre-emergence herbicides run the risk of running out of steam and persistent residual activity could be needed to control a late flush, according to UPL technical specialist Rob Adamson.
He says: “Following the wet autumn so far, growers should consider residual top-ups to boost the persistency needed to achieve successful grass-weed management.”
With no known resistance in black-grass, the active ethofumesate can provide a valuable alternative mode of action in the stack, he says.
Mr Adamson adds that all residuals require care to get the best out of them, whether applied pre- or post-emergence.
“To avoid crop damage, seeds must be covered by 32mm of soil, and it is critical that no rain is forecast immediately after application to ensure the actives remain in the zone they will be most effective,” he says.
Applications of post-emergence top-ups should contain flufenacet as well as alternative modes of
action to best manage resistance, Mr Adamson says.
Targeting black-grass plants at its most vulnerable growth stage will also help to combat resistance, says Bayer technical manager Darren Adkins.
“Small plants with 1-2 leaves are typically more susceptible to post-em sprays like Atlantis OD and Hamlet,” Mr Adkins says.
“At early growth stages, the dose of active can overcome metabolic resistance whereas, large plants in spring are more able to survive.”
Applying additional residual herbicides, mixed with the post-em, or as a standalone top-up, will give crops added protection from weeds germinating in December or January, he adds.
A post-emergence herbicide application also gives an opportunity to consider insecticide requirements.
“Use the T-Sum calculator and crop walking to decide if you need to spray,” Mr Adkins says.
“We have not seen the aphid pressure in Lincolnshire, but in other parts of the country there are reports of aphids.
“Only tank mix if the timing is correct for both weed and aphid control."