Evergreens can go year after year with little or no damage from disease. However when evergreens are stressed they are more susceptible to diseases. Evergreens can be stressed simply by life in the urban landscape. They can also be stressed by weather extremes, exposure, salt, pollution, water problems and soil pH. Transplanting an evergreen can also be a major stress. In the home landscape, we have an interest in the health and appearance of our evergreens. Since evergreens hold the same foliage for several years at a time, preventing or minimizing any damage to their foliage is important.
Concerns about chemicals and how they affect our environment and ourselves have changed our approach to controlling diseases. Our heightened awareness has led to caution about applying chemicals and encouraged taking the time to understand the problem before choosing a plan of action. This planning involves several steps
including prevention, detection, identification, evaluation and treatment options.
Prevention As the old adage says, an ounce of prevention is worth a pound of cure. Plants that are healthy are bothered less by diseases. Not only are they infected less often, if they are infected, the damage is lesssevere. In fact, when a plant is plagued by problems, it is almost always an indication that the plant was already struggling. Knowing this helps us understand that we must treat the whole, not just the symptoms. For the plant, this means being sure that its needs are being met. Whenever there is a disease problem, take a few minutes to evaluate whether or not the plant is getting adequate water, sun/shade or nutrition. Is the soil type right for that plant? Is the pH still correct? Is there too much root competition? Has there been any digging or construction nearby that might compromise the root system? Healthy plants that are getting all their needs met may still be bothered by diseases on occasion, but the impact will be less than on an already stressed plant.
Detection If you suspect a problem with an evergreen, it is important to make sure it is a disease problem before doing anything about it. Look the plant over carefully.
Identification Diseases are usually identified by the symptoms they cause, since laboratory techniques are necessary to identify the exact causative agent. Most diseases are caused by fungi but a few are bacterial or viral. While you can almost always identify an insect problem, sometimes the causes of disease are more difficult. In those cases, all we can do is work to improve the general health of the plant and hope to increase its ability to resist the disease. And, since most diseases are caused by fungi, we can work to minimize conditions that encourage the spread of fungal diseases.
Evaluation Once the cause has been identified, the amount of damage it will do the evergreen can be evaluated. The damage of some diseases is primarily cosmetic, affecting the appearance of the plant. Other damage can also affect the health of the plant. When you know what the disease is and understand what it does to a plant, an informed decision can be made about how to approach the problem.
Treatment There is almost always more than one way to treat a problem and it helps to know the advantages and disadvantages to each alternative. Even when chemical treatments are the best answer, there are usually choices as to which to use.
What Bachman's Can Do For You Bring us a sample - in a sealed plastic bag, please! Bachman's employs many knowledgeable horticulturists who will be glad to help you try to diagnose a disease problem and advise you about alternatives for treatment. If one of our horticulturists is not available or unable to answer your questions, the sample will be passed along for another horticulturist to examine. Occasionally, even we are perplexed by a problem and we may refer you to a certified arborist or the University of Minnesota. Below is a listing of some of the more common diseases associated with specific types of evergreens along with a brief description of the disease and the damage. There are several other diseases that occasionally cause problems to evergreens in our area. If you need more information, please contact Bachman's, a certified arborist or the University of Minnesota. Check at our information desk for help with treatment alternatives.
Spruce When spruce are stressed, they are susceptible to several fungal diseases. We commonly see examples of cytospora canker and rhizosphaera needlecast. Cytospora causes cankers along the larger branches and trunk that then ooze sap and develop white, crusty areas. It usually starts on a few branches low on the tree. The canker cuts off circulation to that branch, the needles yellow first, then brown and the branch dies. Left untreated, cytospora can slowly make the plant unsightly. Like cytospora, rhizosphaera usually starts by affecting a branch or two down low on the plant. It differs from cytospora in that it usually affects growth a year at a time. Looking at a branch infected by rhizosphaera, you will see 2-3 year old growth that turns a brownish-purple and then sheds, leaving that part of the branch bare. Newer growth is also infected but is not showing symptoms yet. Rhizosphaera does not cause cankers on the bark but with a hand lens you can detect black fruiting bodies on the back of infected needles. Left to run its course, Rhizosphaera will bare enough branches to disfigure the tree. Both rhizosphaera and cytospora are most common on Colorado spruce and the diseases are strongly related to the general health of the tree. A less common problem with spruce is another type of needlecast called lirula. Its symptoms are similar to rhizosphaera except that infected spruce tend to hold the affected needles instead of shedding them. Its prognosis is the same as rhizosphaera.
Pine When pines are stressed, they too become susceptible to a number of fungal diseases. There are several types of tip and needle blights. Diplodia tip blight kills new shoots in spring, mostly on Austrian pines. It can also lead to cankers on the trunk and branches. Left untreated, diplodia (a.k.a sphaeropsis) can cause severe damage and eventually kill the trees. Dothistroma needle blight is most common on Austrian pines. Symptoms generally affect lower branches and include spotting on the needles, yellowing, browning and then dieback. It can affect the plants' appearance and health. Pine needles are also susceptible to needlecast diseases. Pine needle rust causes yellow-orange blisters on the needles in early summer. Its damage is mostly cosmetic. White pines are susceptible to blister rust that cause cankers on the trunk. It can severely damage the trees. Blister rust requires the presence of its alternate hosts (currants and gooseberries) to spread.
Juniper Cedar-apple rust is a disease that alternates hosts between junipers (cedars) and apples (or crabapples). On junipers, it manifests itself as a brown gall that grows and exudes an orange gelatinous substance resembling an orange sea anemone. These galls should be removed. If the infestation is severe and/or repeated, consider removing the plant and using a more resistant variety. Also, check the area to find the alternate host. It too should be replaced with a resistant variety. A few times each season, Bachman's sees samples of tip blight in junipers. This is seldom a problem any more because the susceptible varieties are no longer sold by reputable nurseries. Tip blight affects a few tips here and there throughout the plant and throughout the season, distinguishing it from tip die back which happens early in the season.
Other than occasional problems with root rot from excess moisture and/or poorly drained soil, the following evergreens seldom have problems with diseases: Arborvitae, Yew, Fir, Hemlock, Chamaecyparis and Microbiota
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