Smooth Sumac (Rhus glabra)
DESCRIPTION: This shrub forms a spreading crown of dense, multi-stemmed clones. Sumac rarely reaches over 10 feet in height. Bark is light brown and smooth on young plants. Twigs are smooth, stout, angular, and hairless. Leaves are pinnately compound with 7-31 leaflets that are green on the upper surface and nearly white on the lower surface. Leaves turn a brilliant red in fall. On female clones, clusters of red fruit (drupes) develop at the end of the stems in late summer and persist into winter. Each drupe (a fleshy fruit with a hard or stony center) is round, has short hairs, and contains a single seed.
Staghorn sumac may be differentiated from smooth sumac by its densely hairy twigs and petioles, and long hairs on the fruits.
DISTRIBUTION AND HABITAT: Smooth sumac is an opportunistic, native prairie shrub that occurs throughout the U.S. and southern Canada, although it is most abundant in the eastern U.S. This species grows in a variety of habitats, including disturbed sites such as abandoned fields, roadsides, and fence rows; it also grows in native communities such as mesic, dry-mesic, and dry upland prairies, and openings in oak forests. The shrub can be easily recognized throughout the year, but is especially easy to find in the fall when the leaves are red, and in winter when the red clusters of fruit stand out.
LIFE HISTORY AND EFFECTS OF INVASION: This aggressive shrub occurs in clones that spread outward by rootstocks or seeds. It flowers in late May and June, and forms mature seeds by September. Sumac sprouts easily and grows rapidly, but requires direct sunlight to persist. It rarely grows to the size of a small tree. Resprouts grow rapidly and can reach 3 feet in one year. If the clone is left alone and not stimulated to spread by cutting or burning, it will die over time.
Since smooth sumac is a native species, the management objective is usually to keep sumac under control, not to eliminate it. Often when prairies are first acquired, they have not been burned for many years, and sumac may dominate the site. This woody invader can eliminate or reduce the abundance of many other species that cannot persist in the shade sumac creates.
CONTROLLING SUMAC:
With all control methods, the ENTIRE clone should be treated.
Mechanical Control: Cutting during the dormant season or prescribed burning will remove above-ground growth, but sumac will resprout vigorously. In places where dense sumac has shaded out other vegetation, there may not be enough fuel to carry a fire. Growing-season cutting has been found to be effective. Growing-season burning will also probably reduce sumac density. Double-cutting (once in July and once in August) may need to be repeated for several consecutive years to achieve effective control in dense populations. One researcher found that cutting five times over two years reduced sumac density by two-thirds. Another variant is to mow with a sickle-bar every year in mid to late July.
On mesic sites, one technique is to first burn the area in spring (which should increase vegetative cover of other species), then hand-cut sumac stems at ground level in July and August. Sumac will resprout after each cutting, but dense vegetation may prevent sumac from receiving enough sunlight, causing the leaves to turn yellow. Eventually, the resprouts may die.
Mid-summer mowing combined with spring burns to stimulate herbaceous vegetation may effectively reduce the population. Small populations may be kept under control by prescribed burning every three or four years. Because rocky conditions often limit the use of tractors and power brush cutters, hand-cutting with brush nippers is done on such areas.
Chemical Control: Herbicides are effective in eliminating smooth sumac. A stump treatment of 20% active ingredient (a.i.) concentration of glyphosate has proven effective during July and August. However, glyphosate is a nonselective herbicide that will kill most photosynthetically active plants when applied during the growing season. Glyphosate can be applied to freshly cut stumps using either a low-pressure, hand-held sprayer or sponge applicator. Oil-based triclopyr herbicide is labeled for basal treatment. The entire circumference of each stem in the clone must be treated, and no cutting is done.
Foliar applications of water-based triclopyr as directed on label or 1-2% a.i. glyphosate also are effective. Foliar applications should only be done in areas with little or no native vegetation.
CAUTION: Some individuals may react negatively from contact with the juice of smooth or staghorn sumac, which can cause dermatitis (irritation of the skin). Individuals highly sensitive to poison sumac or poison ivy should wear gloves and long sleeves when cutting sumac.
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