Browning of interior spruce needles
caused by Rhizosphaera needle blight.
Rhizosphaera Needle Cast
Brian Hudelson, UW-Madison Plant Pathology
What is Rhizosphaera needle cast? Rhizosphaeara needle cast is one of the most common fungal
diseases of Colorado blue spruce. It can make Colorado blue spruce unsightly and unusable in many
landscape settings. The disease can also affect other conifers including black, Engelmann, Serbian, Sitka, and
white (e.g., Black Hills) spruce; Austrian, mugo and eastern white pine; Douglas fir and western hemlock.
What does Rhizosphaera needle cast
look like?
The first noticeable symptom of
Rhizosphaera needle cast is a browning and loss of
the innermost needles on the lower branches of
spruce trees. Often the youngest needles at the tips of
branches remain healthy. Rows of small, black
spheres form along the length of infected needles and
are visible with a 10X hand lens. These black spheres
are fruiting bodies (i.e., reproductive structures) of the
fungus that causes the disease and are diagnostic.
Where does Rhizosphaera needle cast
come from?
Rhizosphaera needle cast is typically
caused by the fungus Rhizosphaera kalkhoffii,
although other species of Rhizosphaera can be
involved depending on the host. Infected needles,
including those that are still attached to branches and
those that have fallen to the ground, produce spores
that can be blown or splashed to healthy needles.
How do I save a tree or shrub with
Rhizosphaera needle cast?
Consider treating
affected trees with fungicides containing the active
ingredient copper (e.g., Bordeaux mixture) or
chlorothalonil. Treatments will not cure existing
infections, but can prevent additional infections. Apply
treatments every three to four weeks starting as new needles emerge in the spring. Continue applications
through periods of wet weather. For fungicide treatments to be effective, thoroughly cover all needles. This may
be extremely difficult with large trees. Be sure to read and follow all label instructions of the fungicide(s) that you
select to ensure that you use the fungicide(s) in the safest and most effective manner possible.
How do I avoid problems with Rhizosphaera needle cast in the future? The easiest way to
avoid Rhizosphaera needle cast is to avoid planting Colorado blue spruce. If you do plant blue spruce, consider
using dwarf varieties and allow adequate spacing between trees so that branches will not overlap when trees are
full size. Dwarf varieties and properly spaced larger spruce varieties will have better air penetration and needles
will dry more quickly. Dry needles are less likely to be infected. Also check existing spruce trees for the disease.
Remove and destroy any diseased branches and needles by burning (where allowed), burying or hot
composting.
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An EEO/Affirmative Action employer, University of Wisconsin Extension provides equal opportunities in employment and programming, including Title IX and ADA requirements. This document can be
provided in an alternative format by calling Brian Hudelson at (608) 262-2863 (711 for Wisconsin Relay).
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Thanks to Diana Alfuth, Jean Ferdinandsen, Lisa Johnson, Scott Reuss and Amy Sausen for reviewing this document.
A complete inventory of University of Wisconsin Garden Facts is available at the University of Wisconsin-Madison Division of Extension Plant Disease Diagnostics Clinic website: https://pddc.wisc.edu.
University of Wisconsin Garden Facts
For more information on Rhizosphaera needle cast:
See UW-Extension Bulletin A2640,
“Colorado Blue Spruce and Other Conifers Disorder: Rhizosphaera Needle Cast”
https://learningstore.uwex.edu/) or contact your county Extension agent.
Nov. 8, 2018
