Cut-leafed teasel (Dipsacus laciniatus L.) is an invasive plant that is spreading through natural and disturbed areas. No cost effective method of control has been found. Teasel grows for two or more years as a rosette that stays green late in the growing season and begins growth earlier in spring than its competitors. The purpose of this study was to find a time both seasonally and in teasel's life history when herbicides could be applied to decrease teasel with the least impact on the surrounding vegetation. We tested the effects of three different herbicides (Round-Up, Garlon, and Lontrel) on cut and uncut teasel at three different times of the year (July and October 2005, and April 2006) near Clinton Lake in Dewitt Co. Illinois. Photosynthetic measurements were taken before application to determine teasel's susceptibility to the herbicides, and we harvested seed heads and rosettes in October 2006.

Results/Conclusions Results indicated teasel was photosynthesizing at all three application times. Cutting before herbicide application had no significant effect on the number of seeds produced or the dry weight of the rosettes. Herbicide treatment in April significantly reduced the amount of seeds produced, but there were no significant differences among the three herbicides. Lontrel application in April significantly  reduced  rosette dry weight, but none of the herbicides significantly affected rosette dry weight at the other two times. Our studies suggest herbicide application early in the growing season may be beneficial in controlling the spread of teasel, and that mowing will not increase effectiveness.