Sumac can be eradicated but requires special attention to its manner of growth and reproduction. Although it is native, sumac is highly invasive. Allowed to proceed unchecked, it is able to take over a prairie or savanna natural area. The shade under a sumac patch can be enough to suppress virtually all native vegetation.  If the character of a natural area is to be maintained, control of sumac is essential.

A large sumac clone that has established itself in what was once a large prairie

The shade from this dense sumac clone has suppressed all native species

The techniques described here are based on studies and observations done over the past five years on both large and small sumac clones.

Sumac Ecology Sumac is a woody plant that has the potential for forming large clones (thickets). It spreads rapidly and is the single most-important woody invasive plant at many sites. It spreads by rhizomes which form complex underground root systems. In addition to their role in increasing the size of the clone, sumac rhizomes are capable of
sending up myriads of new shoots, called “root suckers.”

Sumac is very sensitive to herbicides such as triclopyr (Garlon 3A and 4),
so that existing stems can be killed by cutting and treating, or by basal bark
treatment. However, although herbicide treatment will kill above-ground stems,
rhizomes and the buds that turn into root suckers usually escape treatment. If
sumac is to be eradicated, these below-ground parts of the clone must be dealt
with. A principal part of the present post focuses on how root suckers can be
eradicated.

Herbicide sensitivity Sumac is sensitive to a variety of herbicides that are active against
broad-leaved plants. One of the best is triclopyr (Garlon).There are two chemical
forms: Garlon 3A is the water-soluble form and is recommended for foliar spraying
(used at 3% concentration) whereas Garlon 4 Ultra is the oil-soluble form and
is recommended for cut stem and basal bark treatments (used at 20% in bark oil). (There are
“generic” versions of triclopyr that are less expensive and but are equally effective.)

Mowing a large sumac clone that had invaded a prairie remnant

Mowing is often recommended as a
means of controlling sumac. What happens when sumac stems are cut? Along
the length of each sumac stem are buds that remain dormant as long as the top
part of the stem is alive. However, if the stem is cut, one or more of these
dormant buds are released and grow. The photo to left shows the response of a sumac stem to cutting. Thus, it is not possible to eradicate a sumac clone by mowing, although mowing can work well as part of an integrated management system.

Fire is often recommended as a way of
controlling sumac. What happens when sumac stems are burned? The terminal
growing shoot and all the buds along the sumac stem are generally top-killed by fire. However, each sumac stem has one or more dormant buds present at
its base. Since these buds are below the soil surface, they are not harmed
by fire. Therefore, when a stem is top-killed by fire, a dormant bud of that stem becomes activated
and sends up a new shoot. Thus, the sumac plant resprouts vigorously when killed by
burning. The photo to the right shows a new shoot just starting from the base of a stem that had been top-killed by fire.

A prescribed burn will generally top-kill all stems of a sumac clone

 What happens when sumac stems are treated with herbicide? When a sumac stem is treated with triclopyr, either with a foliar spray of Garlon 3A, or a cut stem or basal bark application with Garlon 4 in oil, the stem and all its above-ground and below-ground buds are
killed.

The stems of this small sumac clone were treated with Garlon 4 by basal bark. Within a few days the leaves exhibited damage by turning red and within several weeks the whole plant was dead.

Herbicide-treated sumac plants in a short-grass prairie

 Root suckering, an important property of sumac Although herbicide will kill the sumac stem, the network of rhizomes associated with this stem are not affected. Dormant buds will be released and send up vigorous new shoots. These new shoots are called root suckers. (Many clonal plant species produce root suckers.)

Thus, although the above-ground sumac plant can be killed by either fire or herbicide treatment, root suckers are formed from buds within the extensive rhizome complex. In fact, more root suckers may be formed than there were in the existing above-ground stems. Therefore, killing of root suckers is essential if the clone is to be eradicated.

Typical root sucker, arising from the hidden underground rhizome system.

How are root suckers eradicated? Whenever a sumac clone is treated in such a manner that its above-ground parts are
killed, it must be monitored for the formation of root suckers and when they are found they must be killed with foliar
Garlon (3% aqueous Garlon 3A). Each root sucker must be sought out and destroyed. Not all the root suckers appear at the same
time. The timing of this search-and-destroy operation will depend on the growing conditions at the site, and must be done for at least three years.

Locating sumac clones Very large clones are easy to locate. Smaller clones are harder to find but should be given high priority since they have the potential of making larger clones. Since sumac leaves develop intense red color in the fall of the year, this red color can be used to look for sumac clones. Mark each clone, either with GPS or with a permanent marker (wooden stake, rebar, or other suitable marker). Each clone should be given an control number.

Any single sumac plants will not have formed a rhizome system yet. They should be herbicided immediately, using the basal bark technique. (The basal bark technique is effective twelve months of the year and can be used any time a sumac plant is found.)

Canvassing a short-grass prairie for isolated sumac plants

Eradicating a large sumac clone: an example.

Here is an example for southern Wisconsin (probably applicable to other nearby states). This work was done in a high-quality remnant prairie where sumac had become established. On August 1, 2009 the sumac stems of a clone were mowed with
a Stihl brush cutter and all the cut material was hauled away. There were 202
cut stems, each of which was treated with 20% Garlon 4 diluted in bark oil.
Treatment was a combined cut stem and basal bark.

In 2010, the next growing season, the plot was monitored frequently. Root suckers appeared throughout the season and by late summer 183 root suckers had been formed. Note that none of these root suckers arose from the original cut stems. As the tally was being carried out, each root sucker was sprayed with aqueous 3% Garlon 3A. This herbicide treatment was very effective and all root suckers were killed.

Thus, in this study it was possible in three years to eradicate the sumac clone by cutting and treating
followed by treatment each year of all new root suckers.