White Spruce and Needle cast disorder

Asked September 24, 2019, 3:43 PM EDT

I am hearing conflicting information as to whether White Spruce are being affected by the same needle cast issues as Colorado Spruce. Is it the same pathogen? Will White Spruce wind up declining and dying off in a fashion similar to the Colorado types?

Oakland County Michigan

1 Response

This is a difficult question to answer. Although spruce decline is widespread, it is not a certainty that all trees will be affected. It is not uncommon to see healthy, thriving spruce trees near or adjacent to trees that are in severe decline.

The common diseases we see associated with spruce decline are needlecast diseases (Rhizosphaera and Stigmina) and cankers (Diaporthe). Colorado spruce is highly susceptible to all of these. While white spruce is moderately susceptible.

The likelihood of having success can be improved by spruce trees on sites with conditions they favor. Key site factors for spruce trees are full sunlight, good air movement and excellent soil drainage. Avoid planting highly susceptible species in low or shady areas where humidity and moisture remain high for prolonged periods. Follow proper planting practices. Don’t plant trees to close together. This will minimize moisture retention on the foliage and will decrease the likelihood of disease development. When planting new trees in the landscape, space them to allow for optimum air circulation and sunlight penetration into the trees interior. Plan for the mature size of the tree(s) when spacing plants, or plan to remove trees as they begin to intermingle lower branches. Follow proper irrigation practices; keep water off the foliage.

Minimize stress to the trees by water during periods of drought. Control weeds and other vegetation from encroaching around the base of trees to encourage air circulation among and light penetration to the lower branches.

Michigan State University Extension recommends homeowners diversify their landscapes to help make their landscapes more resilient to pest and environmental changes, and seek to plant a variety of species wherever possible.