3 September 1999


NEW herbicide chemistry alone will not solve growers resistant blackgrass problems, says UAP eastern region technical manager Brin Hughes.

"JV485 and AC210 are not the whole answer," he says. "You can get clean fields today with conventional chemistry and current control techniques," he stresses.

The companys prescription for troublesome blackgrass fields starts with taking seed samples in July to establish what resistance type is present. Results from testing are received in time to help with post-emergence product choice.

Before that, the weed burden is reduced with cultivations and a stale seedbed, followed by pre-emergence Avadex (tri-allate). "In every case Avadex improves control from later herbicide treatments. It will always help sensitise the weeds," he says.

Post-emergence herbicides should be applied pre-tillering of the blackgrass, growth stages 11-13 of the weed. That is particularly important where enhanced metabolism resistance is diagnosed. "The bigger the weed, the faster it breaks down the herbicide, and the more likely it is to survive," he explains.

To avoid populations building year on year, 98% control is required, and a mixture of residual and contact acting products recommended.

In UAPs own trials on high blackgrass sites, only Lexus (carfentrazone-ethyl) plus Hawk (clodinafop-propargyl + trifluralin) with oil, or Puma (fenoxaprop-P-ethyl + isoproturon) plus trifluralin with oil hit that 98% target. And that was only when combined with the preceding steps of a stale seedbed and Avadex.

Costing about £46/ha (£19/acre) and £37/ha (£15/acre), such mixtures are not cheap, notes Mr Hughes. "It is quite an expensive way, but it is the only way to get on top of the problem long term." Growers tempted to delay the expense to spring will not achieve sufficient control on larger weeds, he warns.

That is echoed by senior trials officer Derek Lewis. "It means sacrificing some cost for a couple of years, but the problem is not going to go away. It takes 2-3 years to turn the situation around."

Herbicides in the pipeline, pre-emergence JV485 from Twinagro and post-emergence AC210 from Cyanamid, do promise to take blackgrass control onto a new scale. "Alone they are performing better than our best mix, which was Lexus/Hawk," notes Mr Hughes.

But JV485s development has been put on hold (Arable Jul 16) and AC210 may not be available next autumn.

"The new chemistry is interesting but we can do it with the chemistry weve already got," he concludes. &#42

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