Don't plant these troublesome trees in your yard

When planning your garden or landscape, choosing the right trees is crucial – not just for aesthetics, but for the long-term health of your yard.

While many guides suggest the best trees for various sunlight, soil and moisture conditions, few address trees that should be avoided due to their vulnerability to invasive insects and pathogens.

Several tree species are at risk due to non-native insects and diseases. These pests, which often go unnoticed until they cause significant damage, have made certain trees poor choices for planting in your yard.

True firs, including Noble and Pacific silver firs, are under threat from the balsam woolly adelgid (BWA), an invasive insect from Europe. The BWA sucks sap from branches and trunks, causing “gouty” swellings that restrict the tree’s ability to transport nutrients. Trees with severe infestations can die within five years.

White pine blister rust, a fungal disease from Asia, targets white pines with clusters of five needles. This rust has nearly wiped out western white pine populations in many areas, and it continues to threaten whitebark and bristlecone pines. The fungus infects trees through wet needles, with young trees being particularly vulnerable. Pruning infected branches can help, but infection is often fatal once the fungus reaches the main stem.

The bronze birch borer, a native pest, has become a significant threat to ornamental birches, especially non-native varieties. The borer attacks weakened trees, leading to thinning foliage and branch death. Borers damage the tree’s vascular system, making recovery unlikely. Maintaining tree health and selecting resistant varieties are the best prevention strategies.

The emerald ash borer is a bright green beetle that has devastated ash tree populations across North America. The larvae feed on the tree’s phloem, the living tissue in vascular plants that transports the soluble organic compounds made during photosynthesis. This can cause girdling and kill the tree within two years. While not yet widespread in the Pacific Northwest, the emerald ash borer was recently discovered in Oregon, indicating that it’s only a matter of time before it spreads further.

Two diseases threaten beech trees: beech bark disease and beech leaf disease. Beech bark disease is caused by a combination of beech bark scale and fungal infections, leading to tree death within 10 years. Beech leaf disease, associated with a nematode, causes leaves to become leathery and branches to die, killing the tree within six to 10 years. Though these diseases have not yet reached the Northwest, it’s wise to avoid planting beech trees as a precaution.

Every August, as part of National Tree Check Month, residents are encouraged to inspect their trees for signs of invasive pests or disease. Early detection can significantly improve the chances of managing infestations before they become unmanageable. Timely action could save your trees and your landscape.

For more details on these tree species and how to protect your garden, visit the full Ask a Master Gardener blog post at www.skagitmg.org/trees-not-to-plant/. Questions about home gardening or becoming a master gardener may be directed to: Skagit County WSU Extension Office, 11768 Westar Lane, Suite A, Burlington, WA 98233; by phone: 360-428-4270; or via the website: www.skagit.wsu.edu/mg.