Blue Spruce Disease - Port Royal Drive

Asked December 18, 2016, 8:23 AM EST

Fayette Co Ag Agent, We have two small blue spruce trees that were planted approximately seven years ago and have been pruned every other year to remain approximately 7-8 feet high. The area of planting is close to a bedford stone home and has a restricted root growth area. According to the 2007 John Hartman (University of Kentucky College of Agriculture extension plant pathologist) article, I realize the tree is in an area that is subjecting it to drought conditions. We have mulch and will be mulching a large area under the two trees and start a watering plan during dry periods. I researched the common diseases associated with blue spruce trees, to include Cytospora canker and Rhizosphaera Needle Cast. However, the symptoms do not appear to match the condition on our tree. See attached photos, a few branches of one tree has a “white cotton-like” deposit. It has no noticeable smell and can be whipped off by hand. On affected branches, many of the needs have fallen off. Requesting your help to discover the cause and treatment. Thank you, Neil Myers

Fayette County Kentucky

2 Responses

Powdery mildew is a fungus characterized by white hyphae (basic structure unit of fungus) that produce numerous oval white spores which give the infected plant surface a powdery look. Powdery mildew fungi are host specific, i.e. powdery mildew on your Colorado blue spruce is not caused by the same fungus that maybe as the powdery mildew on a nearby peony bush.

A feature of powdery mildew is the fungal spore (conidia) can germinate in high relative humidity conditions rather than standing water, meaning the fungus can be quite severe even during periods of little rain as long as the air is humid.

Treatment with available fungicides is recommended in addition to preventative measures including avoidance of over-fertilization, provide adequate spacing for effective air flow and maintaining a debris-free area to inhibit decaying matter.

You are correct in your assessment of canker and needlecasts. The symptoms and signs are quite different from powdery mildew as well as the disease cycle of each.

The above references mainly treat herbaceous plants however the disease cycle is the same for woody plants. Both articles present fairly complete curative measures.

Hi Bob H.

Thank you sir for the detailed explanation and links for treatment advice!

Appreciate your expertise, time, and effort to respond. Much appreciated!

Wishing you and yours a happy holiday!

Lourrae and Neil