The Empress Tree (Paulownia tomentosa) is a fast-growing deciduous tree admired for its strikingly large, heart-shaped leaves and showy clusters of lavender flowers that appear in spring before the foliage emerges. Native to China, this species can reach heights of 50 to 60 feet. However, the tree’s vigorous nature and susceptibility to biological and environmental factors mean owners frequently encounter maintenance challenges. Understanding these common problems and their solutions is necessary for effective management.
Problems Caused by Insect Pests
The Empress Tree attracts several insect pests, primarily borers and sap-suckers, which pose significant threats to the tree’s health. Borers target the wood of the branches and trunk, causing serious structural damage that is often difficult to detect until an infestation is advanced. The larvae tunnel through the tree’s vascular system, disrupting the flow of water and nutrients, which leads to branch dieback and decline. Prevention is the best defense, focusing on maintaining tree vigor, as borers typically target stressed or weakened trees. For established borer infestations, physical removal can be attempted, or an arborist may apply systemic insecticides.
Systemic treatments are absorbed by the tree and move through the sap to kill the feeding larvae. Sap-sucking insects, such as aphids and scale insects, feed on fluids within the leaves and stems, causing yellowing, distorted growth, and a sticky honeydew residue. Controlling sap-suckers often begins with horticultural oil or insecticidal soap, which smother the insects upon contact and may require repeat applications. Caterpillars feed directly on the large leaf surfaces, sometimes causing significant defoliation. If populations are heavy, a biological control agent like Bacillus thuringiensis (Bt) can be used, which is ingested by the larvae and is harmless to beneficial insects.
Fungal and Bacterial Disease Issues
Fungal pathogens cause many common disease issues in Empress Trees, frequently affecting the foliage, stem, and root system. Leaf spots, such as Anthracnose, manifest as dark or necrotic lesions on the leaves, reducing the tree’s ability to photosynthesize. While often not lethal to mature trees, severe leaf spot can cause premature leaf drop and weaken the plant. Management involves improving air circulation through proper spacing and pruning, and avoiding overhead watering that keeps foliage wet.
Powdery mildew is another prevalent fungal issue, appearing as a white, flour-like dusting on the leaves and stems. This fungus thrives in poor air circulation and is controlled by ensuring the tree is planted in a location with good airflow and ample sunlight. Root rot is a more serious fungal disease correlated with excessively wet conditions, typically resulting from overwatering or poorly draining soil. The fungi attack the roots, causing decay that prevents the tree from taking up water and nutrients, often leading to sudden collapse.
Preventing root rot requires planting the tree in well-drained soil and careful watering practices, especially in heavy clay soils. For newly planted trees, collar rot—a brown or black rot near the soil line—can occur due to overwatering and high humidity. If chemical treatment is necessary for persistent leaf diseases, a fungicide may be applied following label instructions carefully. Sanitation, including promptly raking and disposing of infected fallen leaves, is an effective cultural control to reduce the spread of fungal spores.
Cultural and Environmental Stressors
The Empress Tree’s rapid growth and unique wood properties make it vulnerable to several non-biological stressors. The wood is brittle, resulting in a high tendency for limbs and twigs to break, especially during strong winds or storms. This brittleness necessitates careful structural pruning to maintain a strong central leader and well-spaced branches. Proper pruning in late winter or early spring helps develop a more stable structure, minimizing the risk of breakage as the tree matures.
Cold damage is a significant concern, particularly in regions north of USDA hardiness Zone 6. While the tree tolerates cold temperatures, the flower buds, which form in the fall and persist through winter, are often killed by hard freezes. This loss eliminates the tree’s primary ornamental feature for the spring season. Protecting young trees with a layer of mulch around the base provides insulation for the roots and helps mitigate the impact of extreme cold.
Soil conditions are a major environmental factor. Although the Empress Tree tolerates various soil types, it performs poorly in waterlogged areas. Heavy clay soil retains excessive moisture, contributing to root rot and overall stress. Amending the soil with organic matter to improve drainage or selecting a planting site with naturally well-drained sandy loam is recommended for optimal health.
Managing Aggressive Growth and Invasiveness
The Empress Tree is notorious for its extremely aggressive growth rate, allowing it to quickly establish itself in disturbed areas. Its invasive nature stems from two primary mechanisms: the production of millions of tiny, winged seeds that are easily dispersed by wind, and its vigorous ability to resprout from root fragments and stumps. A single tree can produce millions of seeds annually, which germinate readily in bare soil, making vigilant removal of new seedlings necessary.
The tree also produces numerous root suckers, which are new shoots arising directly from the lateral roots, sometimes at a distance from the main trunk. These suckers must be removed persistently, as even small root fragments can resprout with remarkable vigor. Mechanical removal alone, such as cutting the tree down, is often insufficient because the remaining stump and roots will aggressively send up new growth.
A more effective control method involves combining cutting with an immediate application of a concentrated, broad-spectrum herbicide directly to the stump or fresh wounds on the root suckers. This technique, known as cut-stump treatment, helps the chemical travel down into the root system to prevent resprouting. For owners wishing to control the tree’s size and capitalize on its large foliage, the practice of coppicing—cutting the tree back to near ground level annually—will promote giant leaves but eliminate flowering for that year.