Winter wheat growers are being urged to use contact-type herbicides before the winter to deal with late flushes of blackgrass encouraged by the recent rain.

An extremely dry autumn across most of south-eastern England has led to a delayed chit of blackgrass, but now increased moisture is prompting a green blanket of the grassweed to appear.

Near drought in parts of Essex, Cambridgeshire and Kent saw pre-emergence residual herbicides struggle to work due to the lack of moisture, so experts are saying now is the time to top up weed control.

See also: Herbicide action needed as rain spurs late blackgrass chit

Agronomy group Zantra’s technical director, Chris Bean, who covers some of the worst drought areas of Kent and Essex, says rain in the past few days has encouraged blackgrass to emerge.

“If growers are seeing any significant sign of blackgrass then they should be looking to use a contact-type herbicide and adding in some residual,” he says.

Contact choice

The choice of contact-acting herbicides include Atlantis, Hamlet and Unite, and these can be mixed with a residual-type product based on flufenacet.

Mr Bean advises growers to assess blackgrass populations and look at the history of the grassweed in individual fields. However, he urges them to be vigilant as the efficacy of pre-emergent residual herbicides such as flufenacet, diflufenican and pendimethalin has been hit by the dry weather.

Ed Brown, agronomist with advisory group Hutchinsons in Shropshire, says growers who still expect blackgrass emergence should top up with a residual treatment of flufenacet.

However, if there is a big population of the grassweed through the ground already, he advises not waiting for every last blade of blackgrass to emerge before using a contact spray.

“In the West we still have blackgrass population susceptible to Atlantis, so growers should use that to treat any significant amount,” he says.

Herbicide-resistant blackgrass is not as widespread in the West as further east, while more diverse cropping has prevented blackgrass getting such a firm hold.

Mr Brown adds that there is still an opportunity for growers who have been waiting for blackgrass to chit to get winter wheat drilled at this stage without any significant yield penalty.

New product 

Bayer, which markets contact herbicide Atlantis and new product Hamlet, says the best time to apply these products is when blackgrass is at the one- to three-leaf stage and before it has started to tiller.

Ben Coombs, Bayer’s herbicide product manager, says growers should be prepared to use a contact product as the efficacy of residual pre-emergence herbicides starts to decline after six weeks.

“Our message would be to stay vigilant, be prepared to get on early with a contact herbicide and top up with a flufenacet-based product,” he says.

Bayer launched Hamlet for this autumn. It contains the contact-acting herbicides iodosulfuron and mesosulfuron used in Atlantis plus the residual diflufenican.

It is claimed to give 5-10% better blackgrass control than Atlantis.

Decisions based on blackgrass history

Stuart Jackson, cereals herbicide specialist at Dow AgroSciences, which markets Unite, says growers need to make spraying decisions based on the history of blackgrass in individual fields.

Early-drilled crops with good flushes of blackgrass may need the contact residual approach, such as combining Unite with a flufenacet-based product.

However, late-drilled crops may just need a residual herbicide in the autumn with the contact-acting product left for the spring.

“If blackgrass populations are low in relation to the past, it may be possible to hold the contact product back until the spring,” he says.