Cottonwood trees, members of the Populus genus, are some of the largest and fastest-growing deciduous trees found in North America. They are naturally adapted to thrive in riparian zones, stabilizing stream banks and providing habitat. However, their rapid growth rate is often the source of many problems, leading to structural issues and a generally shorter lifespan compared to slower-growing species. Cottonwoods present homeowners with recurring maintenance and safety challenges.
Common Insect Pests
Cottonwoods attract several insect pests, with some causing significant structural damage and others creating substantial nuisances. The Cottonwood Borer (Plectrodera scalator) is one of the most destructive pests, particularly to young trees. The adult beetles lay their eggs at the base of the tree near the soil line, and the larvae then bore into the roots and the heartwood near the ground. This tunneling weakens the tree’s base, sometimes hollowing out young trees or girdling them near the root collar, which can lead to breakage.
Signs of a borer infestation include the presence of fibrous, light brown sawdust, known as frass, which is ejected from openings in the bark and often accumulates in small piles at the base of the trunk. Other common pests are defoliators, such as aphids, which feed by sucking sap from the leaves. Aphid feeding rarely harms a healthy, mature tree, but they produce a sticky waste product called “honeydew.”
Honeydew drips onto anything beneath the canopy, coating leaves, sidewalks, and parked cars. A black fungus called sooty mold frequently grows on these deposits, turning the leaves and branches a dark color. Another defoliator is the Poplar Tentmaker, a caterpillar that constructs silken webs around leaves, feeding inside the protected space and causing premature leaf loss.
Fungal and Bacterial Diseases
Cottonwood trees are susceptible to a variety of fungal and bacterial diseases, many of which are opportunistic and target already stressed or weakened trees. Cytospora Canker (Cytospora chrysosperma) is a serious fungal disease that creates sunken, discolored areas on the bark of branches and the trunk. The cankers expand in an elliptical pattern, eventually girdling the affected limb or the main trunk, which kills the part of the tree above the infection.
Leaf diseases are common but usually pose less of a threat to the tree’s overall health. Marssonina Leaf Spot is a frequent fungal issue, appearing as dark brown flecks often surrounded by yellow halos. Severe infections can cause these spots to merge into large, black patches, leading to premature leaf drop, although healthy trees often grow new leaves and recover.
Leaf Rust is another common fungal disease, presenting as small, yellowish-orange pustules on the lower surfaces of the leaves, typically late in the summer or fall. Leaf rust rarely causes serious harm to the tree. A bacterial issue, Bacterial Wetwood or Slime Flux, causes a foul-smelling, dark ooze to seep from the bark, indicating bacterial fermentation within the tree tissue.
Structural Weaknesses and Aggressive Roots
The rapid growth rate that makes cottonwoods desirable for quick shade is also the cause of their most significant structural issue: brittle wood. Cottonwood wood is relatively soft and prone to failure, meaning large limbs and branches can break easily, especially during high winds or heavy snow and ice storms. This makes them a potential hazard when planted near homes, garages, or high-traffic areas.
The root system of the cottonwood is also a source of conflict with human infrastructure, being shallow and widely spreading to seek out moisture. These aggressive roots are notorious for lifting and cracking sidewalks, driveways, and paved patios. Seeking water sources, the roots can infiltrate and clog drainage pipes and sewer lines, causing expensive plumbing issues. Thoughtful placement away from structures is necessary to avoid future property damage.
Species-Specific Nuisances
Beyond health and structural concerns, cottonwood trees possess characteristics that are a nuisance to property owners. The most recognized issue is the notorious cotton fluff produced during seed dispersal in late spring or early summer. This white, cotton-like substance is attached to tiny seeds and only comes from female trees, as cottonwoods have separate male and female plants.
This airborne fluff piles up like snow on lawns and driveways. It is highly flammable, creating a fire hazard. The fluff also easily clogs window screens and air conditioning condenser units, reducing their efficiency. Cottonwoods are heavy litter producers, dropping large amounts of leaves and small twigs.