Identifying & Treating Evergreen Diseases

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I often receive pictures from franchisees or from the general public of an evergreen tree that appears to be dying. Although evergreen diseases generally cause a certain pattern when they affect a tree, it sometimes is difficult to provide an exact diagnosis without seeing the tree in person. For example, in the picture to the right, it appears that this Blue Spruce is suffering from a disease, but then again it could be caused by an insect as well. In this case, the franchisee included a close-up picture of the damage, which is helpful. Looking at the damage in both pictures, the cause could be from one of two tree diseases, Rhizosphaera Needle Cast or Stigmina. I recommended that the franchisee perform a simple test to see if either of the two diseases is present. I told him to cut off a small branch near the damaged area, place it in a plastic bag along with a moist paper towel. I then instructed him to seal the bag and wait 24 hours before checking on the contents. After 24 hours, he needs to look at the underside of the needles for the appearance of pinpoint-sized fruiting bodies. A hand lens will be helpful in seeing if the fruiting bodies have appeared and are in rows of two. The other choice he has is to send a branch off to a plant diagnostic clinic, located at many state universities. Since I am located in Illinois, I use the U of I Plant Diagnostic Plant Clinic. There is usually a small fee associated with the test, but you can feel assured that the results are accurate. It is possible that the damage that is displayed in the picture is the result of past drought stress, improper planting, poor tree care or other cultural reasons. That is why it is important to get an accurate diagnosis of the problem. If the damage is caused by an insect, or in the case of Spruce trees, an insect relative, a Red Spider Mite, treating the problem with a fungicide instead of a miticide will not solve the problem. It is also possible that the tree could have both problems going on at the same time. The key to effective disease and pest control is proper identification. You have to know what you are dealing with first to know how to treat it correctly.