Spraying woody plant resprouts at Rettenmund Prairie

Yesterday our crew plus three volunteers (Kathie, Tom, and Michael) spent most of the day spraying woody plant resprouts in areas at Black Earth Rettenmund Prairie that had been burned this spring. This was an excellent time for this work, as the resprouts were big enough to find but small enough to spot spray. Garlon 3A aqueous was used.

The main focus was sumac, gray dogwood, grape, and poison ivy. Although all of these are native, they are all highly invasive and tend to take over. Of these, sumac is the worst.

I have done an extensive study on the history of woody plant invasion at Rettenmund, using early TNC and DNR files as well as old air photos and maps. Sumac has been a problem at Rettenmund since the site was first acquired by the Nature Conservancy in 1986. At the time of acquisition the main focus of restoration was on removal of major aspen clones. Knowledge of how to control sumac was limited and control consisted primarily of cutting with brush cutters. However, cutting alone does not eradicate. Each stem has one or more dormant buds that will be activated after cutting. Burning also does not eradicate, although it top-kills. The next growing season after a burn new shoots will appear adjacent to the killed stems.

Research has shown that the only way to eradicate sumac is with herbicides and triclopyr (Garlon) is very effective. Either basal bark or cut-and-treat will kill the dormant buds. However, because sumac is rhizomatous, it has an extensive underground network, and killing the stems will induce the rhizomes to send up new shoots throughout the area (root suckers). Thus, to eradicate a clone it is essential to also treat all new shoots that appear. One must return to the site over and over until the rhizome network has been exhausted. This may take several years, but it can be done.

It will be necessary to return in a few weeks and canvas the area for missed and newly grown plants. We plan also to return in mid- to late-summer and basal bark any remaining plants. Persistence is the key to eradicating sumac.