Diagnosis of Spruce Problems Requires Good Samples

News Article

During the spring, evergreen diseases begin to show symptoms in Iowa and throughout the Midwest. One of these common diseases is Rhizosphaera needle cast which affects coniferous trees, especially spruce. It is time to get out and look for this disease especially if you have Colorado blue spruce trees.
 
Symptoms will appear in the spring on 1-2 year old needles. Needles will begin to turn brown or purple and will eventually be shed from the tree. When sampling for this disease, it is important to take branches that are showing symptoms but also have a portion of live healthy needles. If all of the needles have been shed from the branch, it is not possible to find signs (bodies) of the fungus necessary for a diagnosis. Samples submitted to the Plant and Insect Diagnostic Clinic should include 2-3 branches that are each about the length of a forearm.
 
One final note to consider when sampling; there is also a very similar but different disease called stigmina needle cast, which is caused by the pathogen Stigmina lautii. Stigmina needle cast causes identical symptoms to Rhizosphaera needle cast; however it is caused by a different fungus. Management options are very similar however some sources indicate that the duration of treatments can be different for the two pathogens.  Get an accurate diagnosis to ensure proper treatment.

Example of a poor spruce sample. Has few needles
Example of an inadequate spruce tree sample with few or no needles present.

Example of a good spruce sample. Has many needles
Example of a good spruce tree sample with symptomatic needles and healthy needles.

Close-up of signs of fungus on spruce needles
Signs of the Rhizosphaera fungus on symptomatic needles.

Microscopic view of needles with fungal bodies
Microscopic view of Stigmina sp. (Left) and Rhizosphaera sp. (Right) fungal fruiting bodies on spruce needles.

Authors: 

Lina Rodriguez Salamanca Extension Plant Pathologist and Diagnostician (Program Specialist II)

Dr. Lina Rodriguez Salamanca is an extension plant pathologist and diagnostician with the Iowa State University Plant and Insect Diagnostic Clinic, a member of the North Central Plant Diagnostic Network (NCPDN) and National Plant Diagnostic Net...