Using fall color to canvas for invasive shrubs

This is peak fall color for shrubs and a perfect time to canvas for areas that need to be controlled. Sumac is the main culprit. Once you start looking for sumac color, you realize how extensive this highly invasive shrub is.

Yesterday I spent the morning (in a light rain!) at Black Earth Rettenmund Prairie locating sumac areas that need to be dealt with. Our goal at Rettenmund is to eradicate all sumac, likely a 4- or 5-year job.

Sumac has been a problem at Rettenmund since the Nature Conservancy first started restoring in 1986. Attempts to control it by mowing and burns have been unsuccessful. According to the recent scientific literature, herbicide is the only solution, and my work over the past several years has confirmed this.

Sumac is an impressive clone former, and left unchecked can take over a natural area. One Great Plains prairie I heard of had become almost 50% sumac! Because sumac causes deep shade, the native prairie flora can be completely eradicated.

Herbicide can be used in two different ways. In the spring we foliar-spray with Garlon 3A all resprouts that have come up after the early burns. This is very effective, and with care there is no damage to nearby prairie plants. However, not all sumac shoots come up at the same time, and because they are small, some can be missed. But at the same time one can spray bramble, honeysuckle, and buckthorn resprouts.

The second way we use herbicide with sumac is as a basal bark treatment (Garlon 4 in oil). This can be done any time of the year, and with care there is no peripheral damage. However, we don't really have time during midsummer to deal with sumac since we are busy with sweet clover.

The off-season (late fall through early spring) is an ideal time to basal bark sumac. At this time of year, all the leaves are off, and the native vegetation has senesced, so that the naked stems are easy to get at. However, at this time of year finding clones, especially small ones, is difficult. This is where the fall-color canvas procedure enters the picture.

While canvassing a prairie, I take GPS coordinates of each clone, and make notes of its extent. Yesterday, I located 16 clones at Rettenmund Prairie, mostly greater than 20 feet in diameter. Obviously, we have some work ahead of us.

In addition to locating clones, it is also useful to locate individual plants that are present scattered across the prairie (see photo below). Each of these plants is a potential clone former, and should be treated with herbicide (basal bark) now.


Finally, I should emphasize that you cannot eradicate a sumac clone with a single herbicide treatment, no matter how thorough. The underground rhizome network is not all killed, and root suckering is a major problem. Therefore, one must return to each clone the following growing season. Early in the season one can foliar spray. Later in the season, it is preferable to basal bark.

At Pleasant Valley Conservancy we have found that it is possible to eradicate sumac clones, but you must keep coming back, at least twice, perhaps three times.