7 March 1997

How to defeat creeping thistle

CREEPING thistle remains a key weed problem in sugar beet due to the biology of its growth and reproduction.

The weed spreads by both seeds and roots/rhizomes, making a correctly timed two-spray programme essential for long-term control, says Donald Westwater of DowElanco.

"The first spray removes apical dominance, the second treatment at the higher rate controls the shoots which subsequently develop from other parts of the rhizome," he explains. "Roots are the quickest and most competitive method of spread, so they must be given priority in a control programme."

Fast spread

Rhizomes can be produced by thistle seedlings as small as the two-leaf stage, he continues. These can spread by as much as 5sq m in the first year. "Even desiccated roots are able to generate new plants, as are sections of roots as small as 2.5cm. Cultivations can make the situation worse.

A two-spray programme based on Dow Shield, with the first 0.5 litre/ha application made when the thistles are at the rosette stage, followed with a 1 litre/ha application three to four weeks later, will give lasting control and protect yields, he concludes. &#42