How do you know when a tree is sick? Well, its actually a science that you can go to school for years to learn. Even more, you still won’t understand everything because just like humans, plants evolve and new pathogens emerge. Pathogens are bacteria, viruses, and other microorganisms that can cause diseases. So, how do you know when your tree has a pathogen or disease? Well, here is a crash course on plant pathology. 

Basic terminology:

First, the definition of sign is “physical evidence of the pathogen” (CANR MSU). When you leave your strawberries in the fridge for too long and they start to get moldy, the white mold is actually a sign (or the physical evidence of the pathogen) of the disease.

Second, the definition of symptom is the “visible effect of the disease on the plant” (CANR MSU). Examples of symptoms include change in color, change in function, and change in shape, like leaves wilting as a result of the disease.

How do you know when a tree is sick? Look for the signs and symptoms!


Upon having an arborist or tree expert out, they might ask you if there has been any recent compaction to the soil near the tree. Compaction causes stress to the roots and could lead to plant death.

In addition, roots do a lot of work to keep the plant alive and healthy, but the main job they have is to uptake nutrients. So, when they are stressed, they won’t be able to do this as well. Symptoms  of soil compaction might look like loss of color to leaves, decaying roots, etc. 

Bark & Trunk:

Like a snake, trees can “shed” bark, and grow new. If your tree is stripping its layers, but not regenerating new ones of bark, then this is a symptom of a disease. Likewise, if your tree shows vertical cracks in the bark, this also can be a symptom of a disease.

On the other hand, if you see fungal spores on your tree, this is a sign and you need to have the tree checked further by a professional. The tree may require removal to prevent further damage to surrounding plants. Fungal spores are, in most cases microscopic, reproductive bodies of fungi. An example of fungi is a mushroom. Not all fungi are bad though, so its best to have your tree checked before removing it. 

Branches & Twigs:

During growing season, your leaves should be showing greenery. If they are not, they are experiencing necrosis, a fancy word for plant death. This is a symptom. If you have dead branches, this is a symptom for many types of diseases, but a common one is root rot. To illustrate, take a twig and break it open. Do you see a bright green? Your tree is very healthy. Do you see a dull green? Your tree is aging. Do you see black or brown? This can mean death to areas of your tree. You should have it checked further. 

Diagnosis of a sick tree:

Surely, diagnosing trees usually requires a pathologist, arborist, or tree service expert. They might ask you how much water the tree receives? You could be over or under-watering. Are you pruning regularly? This is important for the upkeep of your tree. Are you applying mulch at the base of your tree? This protects its against many pathogens and weeds. Are you fertilizing your tree? You could be under or over-fertilizing. 

With this in mind, some common problems in Grand Rapids, Michigan are Anthracnose, Tar Spot, black knot cankers, galls, and wooly aphids. Anthracnose affects Ash, Maple, Sycamore, and White Oak. One way you can determine what is affecting your tree is by taking a sample of the unhealthy and healthy areas of the tree. Following, you should send them into a lab. In fact, there is one located at Michigan State University. Here is a link to their diagnostic lab that goes into more detail on how to send in your samples.

In sum, if you have any questions about how to know if a tree is sick, feel free to reach out to us at any time. Here is a link to our contact form, or give us a call at (616) 430 – 4274!