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Tilia Trees in Portland, Aphids, and Pesticide Advisory

Blog Post
Tilia trees in Delta Park
Tilia is an important tree in Portland’s urban forest. They are adaptable trees that can thrive in a variety of conditions. However, many varieties are susceptible to aphids. There is an Oregon Pesticides Advisory about the use of noenicitinoid insecticides on Tilia trees.

Tilia Names

Tilia is also known as linden for European species and basswood for North American species.

Tilia Characteristics

Bee on tilia flower
Pollinators such as the honeybee shown in the photo are attracted to Tilia flowers.

Tilia forms large trees (65–130 feet tall).

Tilia trees have heart shaped leaves. The leaves are often asymmetrical. The leaf shape is useful in identifying Tilia trees.

Tilia flowers are very attractive to pollinators including honeybees and bumble bees. See the Oregon Pesticide Advisory below.

Tilia Trees in Portland

Tilia is a common tree in Portland: For example, there are:

  • 5,616 Tilia street trees in the City (2.47% of street trees)
  • 413 Tilia trees in Portland parks (1.60% of park trees)

Heritage Tilia Trees

There are Tilia trees designated as Heritage Trees in Portland, incuding

  1. Silver Linden (Tilia tomentosa)
  2. Basswood (Tilia americana)
  3. Bigleaf linden (Tilia platyphyllos)

Oregon Pesticide Advisory

Aphids on linden leaf
Multiple life stages of aphids and sticky honeydew on the underside of linden leaf
  • Tilia flowers are very attractive to pollinators.
  • They are also prone to insect pests such as aphids and thrips.
  • Aphids don't impact the health and longevity of trees.
  • The feeding from aphids and thrips leads to a mess. A sticky substance (honeydew) and cast skins fall to the ground. Black sooty mold grows on the honeydew.
  • Some people might look to use insecticides to deal with the honeydew and sooty mold associated with aphids.

Neonicotinoids and Tilia Species

It is illegal in Oregon to apply certain neonicotinoid insecticides on linden trees, basswood trees, or other Tilia species.

See Oregon Department of Agriculture’s 2015 PESTICIDE ADVISORY Bees and Linden Trees.

Neonicotinoids in Portland

A permit is required to apply pesticides (including insecticides) on street trees in Portland. See Chemical Treatment Permits for details.

Noenicitinoids are not allowed for use on street trees in Portland. See Prohibition on Use and Purchase of Neonicotinoid Pesticides by City of Portland.

Avoid Tilia Location Problems 

Avoid planting Tilia near structures, driveways, and walkways where the aphid honeydew and sooty mold will pose a problem.

For More Information

Aphids (University of California IPM)

Linden Aphid (Washington State University)