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Bayer CropScience is reminding growers about the value of keeping the gap between drilling and pre-emergence herbicides applications as tight as possible.

The period around drilling is vital for weed control with herbicides such as Liberator (flufenacet + diflufenican) offering the potential to achieve up to 80% control of black-grass.

“In trials, we aim to apply Liberator within two days of drilling which is a true pre-em timing and compare this to applications at later dates,” says Darren Adkins of Bayer CropScience. “We see a significant dip in performance at those later dates.

“If grass weeds are an issue, only drilling when there is time and the right conditions to spray is essential. A gap of more than a few days can give weeds the chance to get established and are then consequently tougher to kill.”

Pre-emergence herbicides work by being taken up by the growing shoots and roots of weeds. For example in Liberator, flufenacet is moderately mobile in the soil down to about 5cm and is taken up by roots. Diflufenican remains on the surface and is absorbed by emerging coleoptile and shoots. Once weeds are larger with roots and shoots beyond this zone of activity, the efficacy of pre-em herbicides drops.

As well as keeping the gap until spraying relatively short, there are several other things people will be doing to maintain effectiveness.

“Only spraying when there is soil moisture or rain is forecast is a must because without it, flufenacet cannot move within the soil profile,” continues Mr Adkins. “In previous years, there have been problems when people drill in very dry conditions.”

He advises that delaying drilling from say, mid September to mid October will usually ensure that more soil moisture is available for Liberator to work as well as allowing for potential grass weed flushes to be removed before drilling of the crop.

Rolling between drilling and spraying is also an important step because it consolidates the seedbed promoting germination and also leaves an even surface which is better for herbicide applications.

The other key decision is stacking of actives to use at this timing. “A useful tank mix would be Liberator at 0.6 L/ha with two litres of prosulfocarb, this has performed well in trials and in the field and has been consistent over the last couple of seasons,” says Mr Adkins.

Being strict about the pre-em timing is not without risks according to Mr Adkins: “If you are adamant about keeping the gap short then it is possible that there won’t be the opportunity to drill all the land in autumn. If this is the case the then growers need to be prepared to use a contractor to apply or consider a spring crop instead.