Three-leaf advice to beat blackgrass
AIM to treat blackgrass in wheat when 80% of the weed plants have three leaves.
That is the advice to users of contact-acting herbicides like Hawk (clodinafop-propargyl + trifluralin) from Northants Profarma agronomist Matthew Gaunt.
"That figure is a good compromise to ensure hitting as many emerged blackgrass as possible without letting too many get beyond the three-leaf stage." Control of plants with more than three leaves falls off quite rapidly, especially when dealing with difficult populations, he explains. Blackgrass affects about 80% of farms in Mr Gaunts area which was about three-quarters sown by last week-end.
A good weed flush in many early drilled fields should, in theory, help growers spray at the optimum time. "But it is getting more complicated because wet weather is making it difficult to travel.
"For dense hard to control blackgrass we are looking at the full 2.5litres/ha of Hawk with up to 1000g of ipu for broad-leaved weeds pepped up with 1litre of oil." Depending on choice of adjuvant, control can be boosted 2-4% which could offset the loss of timing flexibility, he suggests.
For lower populations the Hawk dose could be dropped, perhaps to 1.7litres/ha , or substituted by Puma X (fenoxapropo-P-ethyl + ipu), he says. But growers with less competitive canopies from low seed rate drilling should be wary of trimming doses too aggressively, the firms Protex trials indicate.
"A lot of people have been playing with lower seed rates – this could be the year they come unstuck if spraying is delayed," warns Mr Gaunt. *