Common Spruce Diseases: Identification and Management

Overview of Spruce Diseases

Spruce trees are susceptible to several fungal diseases that can cause significant damage if left unmanaged. Understanding the symptoms, pathogens, and effective management strategies is essential for maintaining healthy spruce plantings.

Cytospora Canker

Symptoms: Sunken, dead areas of bark and underlying wood develop on lower branches, girdling small branches within one to two years and larger branches after several years. Resin often flows from cankers and drips onto lower branches. Branch death progresses upward through the tree.

Pathogen: Leucostoma kunzei (formerly Cytospora).

Management: Because the fungus infects wounded tissue and remains latent until drought stress occurs, fungicide timing is ineffective. Select planting sites carefully, avoiding drought-prone locations. Consider the future water needs of a mature tree (50–60 feet tall). Prune out infected branches. Blue, white, red, black, Engelmann, and Norway spruces are all susceptible.

Needle Rust

Symptoms: Year-old needles turn rust-colored in spring and are subsequently cast.

Pathogen: Chrysomyxa weirii.

Management: Destroy heavily infected trees. For protection, apply fungicide at 10% bud break, again one week later, and a third time three weeks after the first spray. Blue spruce is highly susceptible, as are black, Engelmann, red, Sitka, and white spruces.

Rhizosphaera Needlecast

Symptoms: Year-old needles turn lavender and develop tiny black fungal fruiting structures in rows on either side of the midvein on the underside. Large bare areas appear as needles fall.

Pathogen: Rhizosphaera species.

Management: Space trees adequately and control weeds to promote air circulation. Apply fungicide when new shoots reach 1½ inches long and repeat three weeks later to protect young needles from May–June infections. Some locations have a secondary infection period in September–October. Blue and Engelmann spruce are highly susceptible; white spruce is moderately susceptible; Norway spruce is relatively resistant.

Stigmina Needle Blight

Symptoms: Year-old needles turn yellow then brown and fall in spring, a year after infection. Brown needles show tiny black fruiting structures in rows on the underside, sometimes with fuzzy tops. Current-year needles appear healthy.

Pathogen: Stigmina lautii.

Management: Space trees and control weeds for good air circulation. Apply fungicide when new shoots are 1½ inches long and again three weeks later. For best control, repeat applications for three consecutive years.

Cytospora canker on blue spruce.

Rhizosphaeria needlecast.