Beat blackgrass with best herbicide tactics

28 September 2001

Beat blackgrass with best herbicide tactics

A THREE-pronged herbicide strategy against increasingly difficult blackgrass can help prevent variable control, results from a range of trials conducted separately by two leading herbicide manufacturers suggest.

The 43 Syngenta and 46 DuPont trials examined a range of herbicides and timings on sites with hard-to-kill and herbicide resistant blackgrass.

Control from isoproturon plus trifluralin varied from 54 to 74% in five years of DuPont trials and averaged 62% in three years of Syngenta trials on resistant blackgrass sites.

"This is nowhere near the level required to prevent build-up of blackgrass populations," says DuPonts Neil Morey. Control was particularly variable when used without pre-emergence Avadex (tri-allate).

"Of the available alternatives, it was only with robust post-emergence mixtures after Avadex that acceptable control was achieved."

Control from Hawk (clodinafop + trifluralin) plus Lexus (flupyrsulfuron) after Avadex ranged from 91% to 96% in the five years of DuPont trials. The same programme also gave the best control in Syngentas 26 resistant blackgrass trials, averaging 97%. Lexus plus Stomp (pendimethalin) after Avadex averaged 93% at the same sites.

"The need for extra contact activity with dry or cloddy seed-beds or if application is delayed, or in the presence of wild oats, also favours the Hawk/Lexus approach," adds Mr Morey.

On timing, both data sets showed control fell slightly where treatment was delayed from one/two leaf blackgrass to the two/three leaf stage. Delaying until early tillering caused a more obvious loss of control, particularly where no pre-emergence treatment was used.

"Early drilling and low seed rates this year have increased the need for robust control," says Syngentas Iain Hamilton. "Eighty blackgrass plants in a population of 100 wheat plants/sq m can inflict a 40% loss in yield." &#42

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