Colorado blue spruce trees are prized by homeowners for their beautiful blue green needles and symmetrical shape. Unfortunately, the home landscape can be a less than ideal growing environment for these trees making them susceptible to fungal diseases. One of the most common is Rhizospaera needle cast. Learn how to identify and treat this fungal infection.
Identifying Rhizosphaera Needle Cast in Blue Spruce
Rhizosphaera needle cast is a very common fungal infection in spruce trees. While blue spruce is the most susceptible to this fungus, white, black and Engelman spruce are also affected. Only Norway spruce is considered relatively resistant. Rhizosphaera rarely kills spruce trees but does cause enough cosmetic damage to make infected trees unsuitable for home landscapes.
Rhizosphaera first presents symptoms in the late fall or spring following the infection. The first sign will be black fruiting bodies on the tree needles. However, unless homeowners are specifically looking for this infection, it is often unnoticeable. Most often symptoms aren’t recognized until the summer after infection. The tree’s needles will turn yellow, then purplish-brown and fall from the tree. The spruce will lose needles from the trunk outward and travel from the lower branches up the tree.
Early in the season, the ends of branches will appear healthy, but these too will show signs of infection later in the fall or the next spring. If the entire branch appears dead or there is an abundant amount of resin or pitch on the trunk of the tree, the spruce may have another fungal infection called cytospora canker.
Treating Blue Spruce for Rhizosphaera Needle Cast
Rhizosphaera is best treated when identified early before too much damage has been done to the tree. The fungus can be controlled by applying chlorothalonil fungicide (Bravo or Daconil 2787 are two choices) to new growth to disrupt the disease cycle. The fungicide must be applied in late May or early June as new growth emerges. Severely affected trees may require two or more years of fungicide application to control infection. However, the disease can reoccur again at any time. Very large trees require special equipment to adequately apply fungicides and can be costly.
Homeowners can reduce the chance of infection to spruce trees by using good cultural practices. Obviously, starting with good nursery stock is imperative. Inspect trees for infection before planting in landscapes. Properly space trees to allow for mature tree size. Crowded trees are more susceptible to infection. In periods of drought, water thoroughly and fertilize on a regular basis. Also, remove dead or severely infected branches during dry weather.
Rhizosphaera needle cast can severely damage a blue spruce tree but most often won’t kill it. Early identification Rhizosphaera is key to minimizing the affects of infection.
Sources:
Treeful, L. Rhizosphaera Needle Cast. Yard & Garden Brief, P435R, University of Minnesota Extension. http://www.extension.umn.edu/yardandgarden/ygbriefs/p435rhizosphaera.html
Taylor, N.J. and S.t. Nameth. Rhizosphaera Needlecast on Spruce. FactSheet HYG-3059-96, Ohio State University Extension. http://ohioline.osu.edu/hyg-fact/3000/3059.html
Paula Lovgren - Paula is a freelance writer, gardener, garden designer and mother to two children and three cats. She has previously worked as a marketing ...
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