Rhus glabra, or Smooth Sumac, is a deciduous shrub native to North America, not an ecologically invasive species. This widespread plant is found across the contiguous United States and parts of Canada, growing in diverse habitats from dry fields to roadsides. It is identified by its smooth, hairless branches and large, compound leaves that turn brilliant scarlet and orange in the fall. Female plants produce dense, erect clusters of crimson berries (drupes) that persist throughout the winter, providing a food source for wildlife.
Defining Native Aggressive Species
Smooth Sumac is often perceived as “invasive” due to its competitive growth habit, but it is accurately described as a native aggressive species. An ecologically invasive species is non-native and causes environmental or economic harm. Smooth Sumac does not fit this definition because it is indigenous to North America.
Instead, it is a native aggressive species with a strong tendency to spread rapidly and dominate an area. This aggressive behavior is noticeable in disturbed sites, open areas, or manicured lawns where competition is low. Its ability to quickly form dense thickets often leads land managers to view it as a weed that displaces other vegetation.
The Mechanism of Root Spread
The plant’s aggressive nature is linked to its method of vegetative reproduction. Smooth Sumac relies on an extensive network of horizontal underground stems known as rhizomes. These rhizomes spread out from the parent plant, often growing four to eight inches below the soil surface.
This underground system allows the plant to form genetically identical colonies, or clones, by sending up new shoots called suckers. New stems frequently emerge within two to six feet of existing plants. The lateral roots that give rise to these suckers can extend over twenty feet, allowing the plant to quickly colonize a large space.
The rhizomes serve as a substantial reserve of stored energy, making the plant highly resilient to above-ground damage. Attempts to mechanically remove or cut the stems often stimulate the root system to generate more new suckers. This response is a survival mechanism that ensures the species’ dominance following disturbances like fire.
Controlling Smooth Sumac Growth
Managing unwanted Smooth Sumac growth requires methods that focus on depleting the underground root system, not just removing visible stems. Cutting or mowing is ineffective because stored energy in the rhizomes facilitates vigorous resprouting. Mechanical control requires persistence, often involving repeated cutting or mowing twice during the growing season, typically in July and August.
This mid-summer timing is strategic because it coincides with the period when the plant’s carbohydrate reserves are at their lowest point. Repeating this double-cut process for several consecutive years may eventually exhaust the plant’s energy stores. For established thickets, integrating chemical treatment is often the most effective approach.
Systemic herbicides, such as those containing glyphosate or triclopyr, are recommended because they are transported throughout the plant, including the roots. The most efficient application method is treating freshly cut stumps or suckers directly, rather than foliar spraying, which minimizes impact on surrounding non-target plants. Applying a concentrated solution of glyphosate (10 to 20 percent concentration) ensures the herbicide is translocated deep into the rhizome network.