Nine known thistle species exist here in Florida. The weeds — most of which live two years — can be evil-looking in our backyards and pastures.
The key to controlling thistles is to keep them from flowering and producing seeds.
Mechanical or hand removal is effective, but may not be efficient. To hand remove, cut off the entire rosette just below the soil surface or cut off the bolt before it flowers.
This is tedious if you have a large amount of thistle on your property. Mowing can mechanically cut the bolt and stop seed production but is less effective because not all thistles bolt and flower at the same time.
Herbicides are often more flexible and less time consuming. However, timing is important. Thistles in the rosette stage are the most susceptible to herbicides but are hardest to see in the field since they lay flat on the ground.
Once thistles bolt, they are harder to kill with herbicides. Using 2,4-D, thistles are easily controlled in the rosette stage but are only 40 percent controlled at flowering. 2,4-D is an Organo-auxin herbicide, and anyone who applies this herbicide must follow the Florida Organo-auxin Herbicide Rule.
Scouting fields for thistles January through March can save time and money since timing of treatment is important. Herbicide applications during the rosette stage are more effective. If thistles bolt, cut the stalks off before they flower.
The goal is to stop seed production — and, therefore, stop the spread of thistles.
Jennifer Bearden is an agent at the University of Florida's Extension office in Crestview.