Bullthistle in a pasture

       Bull thistle can become a serious weed problem in pastures that are mismanaged. Often in these situations, no measures are taken to control the weed. However, being a biennial plant reproducing only by seed, the plant may be effectively controlled by insects that reduce seed production.

       The seed head fly, Urophora stylata, had been introduced to help reduce bull thistle populations. This insect has successfully established and can have dramatic effects on bull thistle populations at release sites.        

The weevil, Trichosiricalus horridus, was released at one site in Nova Scotia and current status is unknown.
Bull thistle in pasture Bull thistle seed head gall fly: S. Crozier 2005 Urophora stylata: S. Crozier 2005 First year bull thistle rosette fleabeetle on Bull thistle

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Prepared by S. Crozier and M.G. Sampson, 2005