Tree Services Magazine - December, 2012

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Tree Health: Diseases of Spruce and Fir

By John C. Fech

As two of the stalwarts of the conifer community, spruce and fir are generally reliable assets to the landscape. Almost stoic in nature, they provide color year-round, habitat for songbirds, medium-fine texture, vertical structure, low maintenance, screening from undesirable views and a backdrop for shrubs, perennials and other plants.


Radiated heat is an abiotic problem that can cause major stress on spruce and fir.
Photos c ourtesy of John C. Fech, UN L.

However, when something goes wrong, they turn a different color ... literally. Unfortunately, most if not all of the maladies associated with spruce and fir cause a purplish-brown color change on needles and stems. In fact, if you ever want to see a plant pathologist's face turn pale or upper lip shudder, tell them that you're bringing a sample of concolor fir or blue spruce over for diagnosis. The lack of clear delineating symptoms are challenging for experts, arborists and novices alike.

The "lag factor" observed with most evergreens is very common with fir and spruce problems. Unlike disorders of deciduous trees where cause and effect are usually close together in time, the factors responsible for diseases of spruce and fir commonly occur a season or two before the symptoms, which leads to confusion and difficulty with diagnosis. Add this to the "they all look alike" phenomenon and you'll quickly see that diseases of spruce and fir are tough nuts to crack.


At least at first glance, all maladies of spruce and fir produce a similar purplish-brown color.

Abiotic

At least half of the "disease" problems associated with spruce and fir trees are not pathogenic in nature. Instead, the causal agent is nonliving, usually related to the growing conditions in the landscape where the tree resides. A diagnosis of an abiotic cause is usually not well received by a customer; they'd prefer that their tree(s) had some sort of pathogenic disease or insect infestation, because of previous experiences with human disease. Normally, if a person develops an allergy or a urinary tract infection, their doctor can prescribe pills to treat the problem; they're used to this sort of problem-to-cure relationship. In most cases, there's no simple "pill" to solve an abiotic problem.


Slopes present a challenge to spruce and fir, especially in a drought.

The majority of abiotic disorders can be traced back to poor siting in the landscape. Instead of right plant, right place, it's wrong plant, wrong place. Numerous examples can be included, but a few of the more common ones follow here:

<0x2022> Tree on a hill or at the bottom of the hill. Spruce and fir trees located on the upper part of a slope tend to be underwatered, while those sited at the bottom of a hill tend to receive too much water.

<0x2022> Growing in the same space with turf. Since spruce and fir trees require one-fourth to one-third as much water and fertilizer as turf, this lack of separation of turf and ornamentals leads to overfertilization and overwatering of the tree, simply by placing it in an island of turf - a common landscape design flaw.

<0x2022> Severing of roots during construction. Once damaged, roots that once were the conduit of water and nutrients become nonfunctional, which causes a lack of that which is needed most by spruce and fir trees.

Localized site conditions can also stress spruce and fir trees. One of the greatest forces is being placed where reflected sunlight and radiated temperatures burn the needles, causing them to turn purplish brown. This condition may actually be easier to diagnose than other maladies in that large sections of the tree turn brown on one side or in a large mass rather than speckled or spotted throughout the canopy.

Biotic

Although abiotic disorders can cause spruce and fir to fail, diseases caused by living organisms can create major problems as well.

Cytospora canker - The most common canker disease of spruce and fir is Cytospora canker. The first symptom to appear is usually lower branch death. As the disease progresses, one or more branches become affected, eventually killing the tree.

Close inspection is required for this disease, as the actual cankers are often seen at the base of the branch attachment. In general, they are not sunken or of a different color than the rest of the bark, as is the case with other canker pathogens. Like the other canker diseases, however, resin flow is dramatically restricted as a result of infection and deterioration of conductive vessels.

Once Cytospora canker is suspected, cutting into the affected area will reveal brown cambium and sapwood that has ceased to be functional. Needles appear yellow, turning to a uniform brown as the nutrient and water flow cease. Unfortunately, effective fungicide treatments for Cytospora canker are not available. The best approach is to provide best management practices for woody landscape plants which includes separating trees from turf; irrigating to keep soils moist but not soggy; mulching with 2 to 3 inches of a coarse, woody material to cover the roots but not the root flare; control of other pests; and avoidance of compaction, bark and stem injuries.

Rhizosphaera needle blight - While Cytospora canker is primarily a problem of the conductive tissues, Rhizospaera needle cast is a needle-related malady. The infection usually begins on the lower branches and progresses to the upper needles.

Although the new growth becomes infected in late spring or early summer, the symptoms usually do not appear until late summer or fall. Affected needles turn from green to purple-brown and usually drop from branches. Tiny fungal fruiting bodies will be visible using a 10x hand lens, appearing as black dots. During optimal conditions of cool, rainy springs, spores are released and splashed on healthy foliage to spread the disease.

Effective control of this disease can be achieved through multiple applications of chlorothalonil, liquid copper fungicides or manganese/zinc combination products.

Sirococcus shoot blight - Keeping with the theme of all maladies of spruce and fir exhibiting the same symptoms, in many ways, Siroccocus shoot blight is similar in appearance to Rhizosphaera needle cast. Upon closer inspection, symptoms of Siroccocus also resemble frost or winter injury. However, cold temperature injury tends to be uniform, affecting the entire tree or one side of the tree, whereas Siroccocus activity is usually scattered.


Symptoms of Rhizosphaera needle cast.

Siroccocus causes damage to branch tips, especially on the current year's terminal growth. The disease infects the needles of spruce and fir at the base, causing chlorosis in the short term and reddish-brown discoloration (the classic overall symptom once again) in subsequent weeks. In some cases the growth takes on a curled or bent shape, which can be confused with herbicide or insect damage.

Fortunately, Sirococcus infections are usually confined to the lower branches. Sirococcus is also spread through rain splash.

If practical, removal of infected tissues is recommended to reduce spore habitat. Severe infections can be lessened through early spring applications of thiophanate-methyl, propiconazole or liquid copper fungicides.

Lirula needle blight - A lesser-known but still damaging disease, Lirula needle blight can infect all spruce species. Current as well as older growth is susceptible. Sporulation generally begins in early summer and continues until late summer, with the peak in midsummer.

The first symptoms are yellow bands that gradually become purplish-brown (are there any other colors for spruce and fir diseases?) and then expand to cover the entire needle by fall of the year following infection. Smooth, black, fruiting bodies are usually present when the disease is raging, developing along the length of the infected needles. In the end stages of infection, the needles lose the reddish-purple color, becoming pale or tan. In severe cases, spores are also released in subsequent years.

Early summer applications of thiophanate-methyl, propiconazole or liquid copper fungicides will help to lessen the effects. Two to three consecutive years of applications are recommended.

John C. Fech is a horticulturist, certified arborist and frequent contributor located in Omaha, Neb.