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.
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