Fungal diseases affecting non-native evergreen spruce trees
An alarming number of blue spruce trees throughout the Butler area are showing needle loss, dead branches and browning foliage. Many homeowners are rightfully concerned about the potential loss of these evergreens.
Blue spruces were widely planted as landscape trees in the 1970s and 1980s because of their symmetrical shape, rapid growth rate and attractive blue foliage.
However, these conifers are native to the Rocky Mountains and are not well suited to our humidity, extreme temperature fluctuations, hot summers, droughts and late frosts.
This Western Pennsylvania climate combined with the advanced age of many blue spruces is a recipe for stress that weakens the trees, leaving them susceptible to diseases.
The two predominant fungal pathogens attacking our spruce are Cytospora canker and Rhizosphaera needle cast.
Cytospora canker is a fungal disease common to older larger blue spruce trees suffering from the stress of drought, low soil fertility, mechanical injury, insect damage or other diseases.A canker or sunken dead section of the bark forms at the site of infection and over several years enlarges and eventually girdles the branch, which then dies.The disease normally starts on the lowest branches and progresses upward, but can also infect scattered branches throughout the tree.The most conspicuous sign of Cytospora canker is the sticky white resin or sap that coats the cankers and sometimes flows down the trunk.Although there are no chemical controls, careful pruning of the affected limbs in dry weather, using a disinfectant on tools after each cut, is a good way to manage the spread.
Keep blue spruces healthy and less susceptible to the disease by watering during a drought, mulching to conserve moisture and maintain even soil temperatures over the roots, and taking measures to avoid wounding the tree.Although Cytospora canker rarely kills a blue spruce, the branch dieback can create an appearance unacceptable to some homeowners.Rhizosphaera needle cast is another fungus that causes older (inner) needles to turn purplish brown and drop prematurely from blue spruce trees.The infection is usually evident on the lower branches first and progresses upward. New needles do not show symptoms, so the tips of the branches often stay green, while the needles closer to the trunk are discolored and dying.Examining the underside of the needles with a 10x hand lens reveals tiny black spots (the fruiting bodies) in straight rows on either side of the midvein. Because other conditions can mimic Rhizosphaera needle cast disease, identifying the black fungal spots is essential to confirm diagnosis and to guide treatment.There are no control measures that will eradicate this disease, but it is treatable.A fungicide containing chlorothalonil may be applied twice in late spring to protect the new needles, but treatments to large trees can be costly and laborious.
Timing of the applications is critical and reinfection may occur in subsequent years.For the most effective treatment, read the fungicide label carefully and apply only as directed.As was recommended with the Cytospora canker disease, keeping the tree stress free can also help curb the Rhizosphaera fungus.If your blue spruce finally succumbs to disease or you decide to remove it, consider adding a native evergreen to your landscape.Natives are happier with our soils and in our climate and therefore can resist most fungal diseases, as well as insect pests. Eastern white pine, Eastern red cedar, Eastern hemlock, Fraser fir and American Holly are great choices for our area.If you have additional questions about diseases of blue spruce trees or other plants, call the Master Gardener Greenline at 724-287-4761, Ext. 229.
