Limited post-emergence herbicide options for controlling blackgrass in winter barley mean pre-em sprays are critical, Bedfordshire-based Vass agronomist Andy Scott says.

“Blackgrass resistance to fop and dim chemistry, such as Tigress Ultra and Grasp has put considerable strain on post-emergence residual herbicides such as isoproturton and Stomp. We don’t want to go backwards with the weed seed bank, so we have to get on top of the problems early.

“In wheat we have Atlantis, but we have already seen the number of resistance cases treble in one year, so we can’t rely on this new chemistry.”

But in barley he thinks including Lexus SX in the pre-emergence strategy with Crystal and Treflan offers an effective alternative given good seed-beds and moisture. It improves the receptiveness of emerging blackgrass to post-em sprays such as IPU, he says.

In trials at Houghton Conquest in Bedfordshire last year, this new strategy saved about £12/ha over Crystal followed by IPU/Treflan then Tigress Ultra or Grasp (total cost of £79.50/ha), but achieved the same level of control.

“Our recommendation this year will be pre-emergence Lexus SX at 20g/ha plus Crystal at 2 litres/ha followed by early post-emergence IPU at 5 litres/ha plus Treflan at 2 litres/ha, hitting the blackgrass early while it is still small.” Lexus SX is only approved for pre-emergence use in barley, but has more flexibility in wheat, where it can be used pre/peri or post-em, he notes.

Despite concerns within the industry of increasing sulfonylurea resistance, Mr Scott does not believe that including Lexus pre-emergence in the barley spray programme will greatly increase SU resistance build-up.

But Norfolk-based Andrew Blazey from The Arable Group disagrees, preferring to preserve the use of SU chemistry for other crops (eg, Atlantis in wheat). “I wouldn’t like to go down the Lexus route in barley and from what I’ve seen, it’s doing next to nothing on blackgrass anyway.”

He suggests using an approach based on full rate Crystal, followed by IPU/Treflan, and Axial if oats are a particular problem.

Limited options

Given the limited options for controlling blackgrass in winter barley, AICC agronomist Bryce Rham says growers may need to reconsider growing the crop where blackgrass is a big problem.

“You’re not getting the yield of winter wheat, yet you may be using similar chemistry. If you’re only getting 3t/acre instead of four with wheat, why grow winter barley on bad blackgrass areas?”

Pre-emergence options are generally limited to Crystal, Liberator, Defy and Lexus, while IPU, Stomp and Tigress Ultra are the key post-em options, he says. Full rate Axial can also be used against blackgrass, but may be more expensive than other products.

Its main strength is against ryegrass, he says. “Axial is a very good product in winter barley against ryegrass and winter oats, but the rate for blackgrass is very high.”

Growers need to be careful when choosing products and timing in winter barley, Mr Rham stresses, as the crop is not as resilient as winter wheat and poor product choice, rate or timing could result in crop damage.