Sawtooth sunflower at Rettenmund Prairie out of control!

Sawtooth sunflower (Helianthus grosseserratus) is predominantly a wet-mesic species but under some conditions can invade mesic sites. Although tall and showy, it is not especially desirable. Just like other sunflowers, it is clonal, spreading by shallow-rooted rhizomes. In keeping with its commonality and weedy nature, it has a Coefficient of Conservation of 2.

Until this year at Black Earth Rettenmund Prairie we had seen only small amounts of this species, primarily at the edge of the Gateway Prairie. We have been keeping it under control by cutting and treating the cut stems with 20% Garlon in oil. Although this procedure was developed for control of woody plants, it can definitely be used for perennial herbaceous plants as well. (We also use it for creeping bellflower.)

Although we had eliminated sawtooth sunflower last year in areas we had located, suddenly it is all over the place, and mostly in habitats that would be called dry-mesic or dry. The photo here shows the dense stand along Fesenfeld Road. Although not visible in the photo, sawtooth has also spread into the high-quality prairie remnant behind. where it is starting to make substantial clones.

Monoculture of sawtooth sunflower along Fesenfeld Road.

I suspect that these dense stands are the end result of last year's serious drought. Many of our good prairie plants were killed, especially grasses such as little bluestem. Lots of bare areas were created, where sturdy plants such as sawtooth could grow and spread out. Then the very favorable rainfall this year encouraged them to flourish. While managers were spending their time monitoring for the usual culprits (sweet clover, wild parsnip), sawtooth was becoming well established. We didn't notice until it flowered. The end result is what we are seeing now.

Is this a permanent replacement, or will the habitat revert to its former status? Only time will tell. In the meantime, we should be eradicating sawtooth in areas like that shown above. The only problem is that we have lots of other things to do as well. Perhaps this sawtooth patch will go away on its own?