April 12, 2002 | By: Laura Skillman

Every year thistles can be found across the state and these noxious weeds are often a thorn in the side of Kentucky’s hay and livestock producers and land owners.

Once established, these weeds are difficult to eliminate but can be curtailed using several control techniques, said J.D. Green, University of Kentucky Cooperative Extension Service weed scientist.

Musk thistles, also called nodding thistle, are the most common thistle plant in Kentucky covering a wide band of the state from around Bowling Green to Northern Kentucky. They reproduce by seed so a major aspect of any control effort is to limit seed production.

“Most people don’t initiate control efforts until it produces flowers,” Green said. But, that is too late.

The plant’s life cycle begins in the fall with germination and the formation of a rosette close to the ground that often goes unnoticed. In the spring the plant begins to grow, forming flower stalks followed by bright purple to reddish flowers in late May to early June. Stopping the plant from flowering is the key to preventing spread of the weed.

If left unchecked, thistles can become pretty dominant in hay and pasture fields, particularly those with thin or bare areas, Green said. These areas are ideal for the seeds to be deposited and to germinate. March and April are some of the best times of the year for using chemical control efforts.

Broadleaf herbicides labeled for use in pastures can be used to control thistles but they must be appplied prior to flower stalk elongation for effective control. This needs to be done now, Green noted. The bigger the plants are, the more difficult it is to control them using herbicides, he said.

The Kentucky Department of Agriculture has a noxious weed program using demonstration plots conducted against these noxious weeds including thistles. Each demonstration plot consists of 10 acres sprayed for the control of thistles at no cost to the farmer, and an additional 10 acres can be sprayed if the farmer supplies the materials. The plots are designed to demonstrate proper timing, chemicals and equipment necessary for effective control. The program is available to 10 to 15 farmers per county. For information on the program contact Bill Fraser at (502) 573-0282 or by e-mail atbill.fraser@kyagr.com

Thistles can also be controlled mechanically by mowing or clipping pastures, Green said. This must be done before seed heads begin to open. Thistle plants mowed or removed by hand after blooming contain enough energy reserves that they can still produce viable seeds.

Biological controls are also possible. A thistle-head weevil can be found in central Kentucky in the spring and this weevil feeds on maturing seed inside the developing flower head. It will not eliminate all seed production but can significantly lessen the amount of seed produced, Green said.

“Whatever method is used, do it at the right time to reduce seed production,” he said.


JD Green 859-257-4898