Clemson Extension Forestry and Wildlife

Wisteria is in Bloom Across South Carolina

Large, showy, purple wisteria flowers are covering trees along roadsides this time of year. While they are pretty, most of what you are seeing is also invasive. Several wisteria species live in South Carolina. American (Wisteria frutescens) and Kentucky wisteria (W. macrostachya) are native species. They are not all that aggressive in terms of their growth. However, it is an entirely different story with non-native invasive Chinese (W. sinensis) and Japanese (W. floribunda) wisteria. These are aggressive plants that will grow up and take over old buildings, trees, or anything the vines can grow on. Telling the wisterias apart can be difficult, but there are some ways to do so. Chinese and Japanese wisteria flower during leaf-out, while the native species flower later in the season, after the vines have leafed out as shown in figure 1. Flowers on the invasive species are also almost twice as long as those on natives as shown in figure 2, and native flowers are unscented. Also, seed pods are smooth on the native species and fuzzy on the invasive species. And, they twine differently around whatever they are growing on. Native and Chinese wisteria twine clockwise, while Japanese wisteria twines counterclockwise.

Figure 2. Long flowers of the non-native invasive forms of wisteria Photo Credit: Dave Coyle, Clemson Extension.
Figure 2. Long flowers of the non-native invasive forms of wisteria Photo Credit: Dave Coyle, Clemson Extension.

Wisteria’s large woody vines can strangle smaller trees, and the weight of the vines, foliage, and flowers can cause tree limbs to break. What is worse though, in forest stands with wisteria the vines can tie the tops of trees together as shown in figure 3. This causes a very dangerous situation for anyone trying to harvest those trees- can you imagine a feller buncher trying to remove trees that are all tethered together at the top? To remove wisteria from a forest stand that will be harvested, it is best to cut the vines a few years prior – but do this in winter. If you cut vines in summer (when they are full of water) they can choke out living trees as they dry out and constrict. To kill wisteria, foliage can be treated with triclopyr or glyphosate. Cut stems can be treated with triclopyr. When the wisteria is very tall, a combination of cutting the vines and later spraying the regrowth foliage may be effective.

The article was originally featured in the Spring 2020 Edition of the CU in the Woods newsletter.

Figure 3. Wisteria vines overtaking large trees Photo Credit: Dave Coyle, Clemson Extension.
Figure 3. Wisteria vines overtaking large trees
Photo Credit: Dave Coyle, Clemson Extension.

 

Author(s)

Dave Coyle, Cooperative Extension, Forestry and Wildlife Specialist

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