Marking out patches of thistles in sugar beet crops now will make it easier to target second spray applications and improve overall control of the weed, growers have been told.

A normal sized thistle patch of four stems per square metre can cause yield losses of up to 4t/ha, so fully controlling the weed is vital, said Martin Lainsbury, British Beet Research Organisation’s technology transfer officer.

Thistle re-growth after the first spot treatment is often difficult to spot from the sprayer or tractor cab as foliage collapses back into the crop and the sugar beet canopy has closed over, he said.

“Spot treating thistles with DowShield (clopyralid) is common practice, usually over two applications. But growers can fail to fully control thistles because they are so difficult to spot on the second application.”

Growers should mark thistles at the first herbicide application with stakes or flags, or precisely position onto a field map with a hand-held GPS-receiver, for use in the sprayer cab later, he added.

See the Growers Guide at www.uksugarbeet.co.uk for more information.