Practical Technique to Manage Smooth Sumac and Maintain Prairie Biodiversity (Nebraska)

Historically, smooth sumac (Rhus glabra) was considered to be a minor species occurring at relatively low densities on most tallgrass prairies in North America. This native shrub was generally restricted to ravines and other areas protected from disturbance, particularly fire. Changes in disturbance regimes allowed it to increase rapidly and form dense thickets, threatening prairie biodiversity and productivity (Kaul and Rolfsmeier 1987, Tunnell et al. 2006a).

Shifting the plant community from shrubland/woodland to prairie is an important goal of many managers of prairie remnants and restorations. We were concerned about the continual increase of smooth sumac on Nine Mile Prairie, a 93 ha tallgrass prairie remnant in eastern Nebraska. By 2003, foliar cover of smooth sumac was about 25%, and patches of smooth sumac had a density of about 2 stems/m2. Smooth sumac is not controlled by modern prescribed burning practices that are typical for prairie management but do not emulate historical fire disturbances (Stubbendieck et al. 2003). Broadcast herbicide application can control smooth sumac, but it frequently negatively influences plant biodiversity (Tunnell et al. 2006b). After several years of experimentation at Nine Mile Prairie, we developed a three-step technique of prescribed burning, shredding the top-killed smooth sumac, and wick application of herbicide that has proven quite effective and has not decreased forb frequency or richness.

Before developing this technique, we evaluated various rates and combinations of 2,4-D LV ester, 2,4-D amine, picloram, and triclopyr applied in June, either as a broadcast spray or with a wick. A handheld wick (Sideswipe, Custer SD) was used to apply the herbicide directly to the smooth sumac foliage. We determined that all tested herbicides effectively controlled this shrub (Tunnell et al. 2006a). Overall, plots in which the herbicides were applied with a wick had greater forb frequencies and forb species richness than plots where the herbicide was applied as a broadcast spray.

Figure 1.

Shredding smooth sumac (Rhus glabra) after prescribed burning in Nine Mile Prairie in eastern Nebraska.

Photo by J. Stubbendieck

While the wick-application treatments were the best to maintain forb biodiversity, we determined that it was not practical to use a handheld wick to treat infestations of smooth sumac larger than a few hundred square meters. Therefore we acquired a tractor-mounted rope wick designed to apply glyphosate to tall weeds in soybean fields. The herbicide solution is placed in a PVC tube from which the ropes emerge and are wiped against the target plants after becoming saturated with herbicide. Both instructions for construction and suppliers of rope wicks can be found online.

We learned that the rope wick applicator could not be used successfully on mature stands of smooth sumac because the stiff, woody stems and branches pulled the ropes out of the couplers. Therefore, we used a tractor and a shredder to cut back the smooth sumac stems, which varied in height from 0.1 to 4 m, to the soil surface (Figure 1) and then treated the less woody regrowth. However, cut smooth sumac stems can puncture tires, and equipment should have heavy-ply or foam-filled tires to prevent flats. Even though our research showed that prescribed burning did not improve control, we found that it was easier to shred smooth sumac after burning eliminated the aboveground prairie biomass.

Figure 2.

Rope wick used to apply herbicides to smooth sumac (Rhus glabra).

Photo by J. Stubbendieck

We waited until June to allow new smooth sumac shoots to grow above the prairie plants before wiping the herbicide directly onto the smooth sumac foliage (Figure 2). When the tallest prairie grasses were about 0.5 m tall, the rope wick was set at a height of about 0.7 m. Where smooth sumac was dense, we had to drive slowly or make an immediate second application perpendicular to the first to apply an adequate amount of herbicide for control. The label guidelines need to be followed, but the herbicide concentration is greater (about...