There are a wide variety of non-native invasive plant species that have taken hold in Madison County. These plants cause harm to the environment, as well as potential harm to human, animal, and plant health in the preexisting environment. Some of these damages can be caused by overtaking beneficial native plants in the ecosystem, act as vectors for diseases and other invasive species, such as invasive insects, and are unhealthy or potentially toxic to native animals. In this series, we will discuss identification and control of these prevalent invasive plants.
Identifying Princess Tree
The Princess Tree (scientific name Paulownia tomentosa) is a woody deciduous tree in the empress-tree family. This tree is native to China, and other regions of eastern Asia, and can tolerate moderately cold conditions. Princess tree is a fast growing tree, able to grow up to 15 feet in a single year if growth conditions are ideal until it reaches its mature height of about 50 feet. This invasive tree can reach its full mature size of 50 feet tall, and 30 feet wide in ten years. This height and width are visible in a rounded canopy that produces dense shaded areas due to the massive leaves growing on its limbs. Each leaf on this tree is oval or heart shaped and covered in velvety hairs on both the upper and lower sides of the leaf surface, and grows anywhere from 5 to 12 inches in size. Young trees and regrowth from cut stumps can have leaves double the size of those on a mature tree. Another identifying feature of the princess tree is the thin, grayish brown bark that covers the tree, split with shallow fissures across the surface. This tree does not produce flowers on any of its first year growth, but on more mature growth (second year and older), the princess tree will produce clusters of pink or lavender flowers. These flowers bloom in the spring, usually from April to May, and appear on the branches before the leaves emerge. The flowers are fragrant, almost vanilla scented, and funnel shaped, and grow to about 1 to 3 inches in size, which can make the flower clusters approximately 12 inches in size. The fruits produced by this invasive species are oval shaped seed capsules, first appearing sticky and green, and drying out into brown, woody-textured capsules that remain on the tree throughout the winter. When the capsules fall, they burst open and release large amounts of small, winged seeds that fall all around its surrounding area.
Princess trees can grow in a wide variety of environments, as they are tolerant of many different soil types and environmental conditions. They can tolerate soil types of a wide range, including dense clay soils, silt or loam soils, sandy soils, and even rocky soils or soils with high organic matter content. This invasive plant’s tolerance of various soil acidities as well, ranging from acidic to neutral to basic, which allows it to grow in areas with less competition. You can view photos of the Princess tree through the NC Extension Gardener Plant Toolbox.
How It Spreads
The princess tree was originally introduced into the United States for ornamental purposes, and has since spread widely across the entire continent of North America, spreading from Montreal to Florida down the east coast, and as far west as Texas. This invasive plant’s ability to tolerate cold has made it prolific even through areas of the US that may have harsher winters than we experience in the Southeast, and keep it competitive in the environment when winter weather arrives. The extremely fast growth pattern of the princess tree makes it a fierce competitor in the environment, often outcompeting more beneficial native species in the ecosystems they have invaded. It can often be found in disturbed natural areas, including forests, streambanks, and even steep, rocky slopes where other trees and foliage may struggle to grow. Its ability to tolerate harsh environments like acidic soils, drought, and low soil fertility have contributed to its appearance along areas such as roadsides being an ideal habitat for this invasive species to thrive. A single, mature princess tree can produce millions of small, winged seeds that can be dispersed throughout the environment they are in, and its prevalence around roadsides means that these seeds can be transported far and wide due to the movement of vehicles that may carry the seeds from place to place.
Controlling Princess Tree
As mentioned earlier, the princess tree was first brought to the United States and planted as ornamental trees, and it is often still planted as landscape decoration throughout the country. Because of this, and its ability to live in a wide variety of environments, the princess tree is a difficult invasive species to control in the environment. One of the most important steps that can be taken to control this invasive plant is to try to prevent the propagation and planting of it as landscape ornaments. Once it is already established, there are a few potential methods of control that could be implemented to help control and prevent the further spread of princess trees.
The first method of control is known as mechanical controls. The success of this method is highly dependent on the stage of life that the princess tree is currently in. When the tree is still just a young sapling, no more than half an inch in diameter, it can be pulled by hand when soils are moist to reduce the chances of root breakage. Caution must be taken when pulling though, as any broken pieces of root left behind could potentially resprout as a new princess tree. Using mechanical methods like cutting on the princess tree are not considered effective, as the existing root system of the tree will send up shoots across the entire root system, causing potentially multiple new trees to appear within feet of the originally cut down tree.
Methods of control that are considered more effective for the princess tree involve the use of chemical controls. The first method of chemical control is known as a foliar application of herbicide. A foliar application can be used on small trees and seedlings as an effective method of control using a 3% solution of a non-selective herbicide such as glyphosate with 0.5% of a non-ionic surfactant included. This surfactant helps the herbicide to stick to the leaves of the plant, making the application more effective at controlling the invasive plant. Thoroughly spray the leaves with this mixture, making sure all leaves are wet for the best control.
Young trees up to six inches in diameter can be controlled using a method known as basal bark treatment. This treatment should be used with caution, as it requires the use of a large amount of herbicide, and can result in overspraying that could damage surrounding plant life that is desirable to keep. This method is most often used in areas where there are few other plants around, or in exposed sites like cliff faces. To do this application, use a solution of 25% triclopyr ester (such as Garlon 4), a selective herbicide made to target woody plants, and 75% mineral oil base. Spray this solution around the base of the tree, from the ground up to 12-16 inches from the base during the late winter or early spring for the most effective application.
The final chemical control method that can be used is effective for mature trees, and is known as the cut-stump method. This method is a sort of combination between mechanical control and chemical control, as it first requires the tree to be cut down within 6 inches of the ground, and then the newly formed stump to be sprayed with a solution of 50% triclopyr immediately after cutting. When using this method, the freshly cut stump must be sprayed within the first three minutes of being cut to be most effective due to turgor pressure within the trunk of the tree. Turgor pressure is caused by the pressure of water within the plant cells that allows the plant to keep its upright and rigid structure, as well as aiding in the flow of nutrients across the expanse of the plant, from the tips of the leaves to the ends of the roots underground. The lingering presence of this turgor pressure after the princess tree has been cut helps with plant absorption of the herbicide used to control this invasive species. This act of spraying after the trunk is cut must also be done quickly due to the fact that plants have the potential to scab over injuries to protect themselves. Once they have formed that callused scab over the stump, the tree will no longer absorb any of the herbicide. This method is most successful when applied during the late summer to fall, when the plant is redirecting its nutrient flow back down into its root system. The cut-stump method is also more forgiving of inclement weather than the foliar application method, and provides a more targeted application of herbicide to the desired plant, preventing the issue of overspraying or causing potential harm to other plants that may be desirable in the surrounding area.
All of these methods are effective control of Princess Trees, but even after treatment it is important to monitor and control basal sprouts or root suckers that may appear to ensure that this invasive species is eradicated after treatment.
If you have any other questions about identifying or controlling Princess Trees, please contact N.C. Cooperative Extension, Madison County Center at (828) 649-2411, or reach out to me directly at peyton_duckett@ncsu.edu.
Citations
Invasive Species Leaflet. (2010, March). NCDA&CS, Forest Service Division.
North Carolina State University. (n.d.). Paulownia tomentosa. North Carolina Extension Gardener Plant Toolbox.
