One of the most common plants in our landscapes is the Colorado spruce. Some people know it as blue spruce, even though a blue spruce is just one of many types of Colorado spruce.
Rhizosphaera and Stigmina needle cast diseases of spruce are definitely an issue here in Pulaski County. In fact, it's become more problematic than some of the other problems associated with spruce, like spider mites or bagworms.
Rhizosphaera is the most common disease of spruce in Kentucky. Stigmina is less common but causes symptoms similar to Rhizosphaera.
Symptoms of both needle cast diseases becomes evident in the summer when needles on lower branches turn purplish or brown (Figure 1). Needles fall within a few weeks and lower limbs are left bare (Figure 2).
In order to determine whether Rhizosphaera of Stigmina needles cast is present, infected needles should be inspected with a hand lens. The type of fungal fruiting body emerging from stomata confirms one or the other.
Rhizosphaera - small, dark fruiting bodies (pycnidia) appear as tiny raised, grayish bumps (Figure 3). While most easily seen with a hand lens, they may be visible without magnification.
Stigmina - fungal fruiting structures (sporodochia) appear as tiny, brown to black, brush-like tufts emerging from needles (Figure 4).
Like other fungal diseases, needle cast diseases infect during wet weather throughout the spring and summer and are spread by water splash or wind-driven rain. Symptoms occur anywhere from a few months up to a year after infection.
If you feel like your spruce may have either of these diseases, be sure to call and arrange a visit or bring in some affected foliage to the Extension office. They are fairly easy diseases to diagnose.
There are no cultural controls for this disease except to rake up the fallen needles or add a new layer of mulch over fallen needles.
Stressed trees are more susceptible to infection than healthy plants so be sure to maintain plant vigor. Insure good air circulation so that wet needles dry off quickly.
Remove highly infected trees. Prune out badly infected branches then be sure to spray a fungicide to protect remaining foliage. Fungicide should be applied when the new needles are emerging in the spring.
Chemical control is mainly chlorothalonil (brand names Daconil, Fungonil). Copper or mancozeb can also be used. Trees with a history of the disease may need to be protected two consecutive years.
When considering plantings for your landscape, Colorado spruce may not be a preferred plant due to this potential disease problem. Other spruces are susceptible but not to the extent that Colorado spruce is.
For more information, contact the Pulaski County Extension Service at 606-679-6361 and request the University of Kentucky publication ID-85 'Needle Cast Diseases of Conifers'.
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Join us for a class called Stump the Extension Agent on June 20 at 6pm. The focus will be on weeds so bring in any problematic weeds and we'll discuss management options. The class is free.
The Lake Cumberland Master Gardeners have pine straw mulch for sale at the Pulaski County Extension office. It is sold in bales for $7 per bale (over 50, $6 per bale). It can be purchased during office hours 8am to 5pm Monday - Friday.
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