Diseases that Affect Trees

Despite trees being a source of medicine and herbs that treat diseases and wounds, they are also prone to infections. Like other living organisms, these diseases can be diagnosed and treated accordingly.

Trees can be affected by various diseases such as bacterial, fungal, viral, parasitic, insect or nematode infections. These diseases may cause the tree’s death or lead to its decline in health.

Diseases that Affect Trees

Here we have listed 3 of the major categories of the most common diseases that affect trees:

1) Bacterial Diseases

Bacteria are one of the most common causes of plant disease. They are microscopic single-celled organisms that grow fast. The bacteria are usually found on dead leaves, bark, branches, twigs, roots, and soil.

Bacterial diseases can be divided into two categories – systemic and non-systemic. Systemic illnesses spread through the entire body of the plant, while non-systemic diseases attack only specific parts of the plants.

Common bacterial diseases include black spot, bacterial leaf blight, damping-off, crown gall, fire blight, gray mold, root rot, Septoria Leaf Spot, Sudden Oak Death Syndrome (SOD), white rot, etc.

The symptoms that could let you know it’s a bacterial disease include:

  • Darkening of the foliage
  • Yellowing of the leaves
  • Stem dieback
  • Branch dieback
  • Foliage drop
  • Wilt
  • Brown spots on the leaves

Bacterial diseases in trees can be treated using fungicides, pesticides, biological control agents, and antibiotics. However, if the problem is severe, then pruning should help.

2) Fungal Diseases

Another group of microscopic organisms that grow real fast is fungi. They are usually present on decaying matter and infected wood. Common fungi include powdery mildew, rust, anthracnose, brown blotch, blue stain, etc.

Symptoms that could indicate a fungal infection include:

a) Water-soaked lesions on the leaves

b) Severe wilting

c) Blackened areas on the leaves

Fungicide sprays, fungal oils, copper-based products, sulfur, and lime sulfur are some treatments available for fungal-based diseases attacking a tree.

3) Viral Diseases

Viruses are tiny infectious agents that replicate inside the cells of their host organism. They are responsible for causing many different kinds of diseases. They are nucleopolyhedrovirus, cauliflower mosaic virus, tobacco mosaic virus, potato virus X, tomato bushy stunt virus, cucumber mosaic virus, etc.

The main symptom caused by viruses is the yellowing of the leaves. Other symptoms include stunted growth, deformed leaves, distorted flowers, mottled leaves, necrosis, premature senescence, withering, etc.

Viral diseases in trees are the most troublesome to eliminate because viruses do not respond to treatment because they mutate quickly. Therefore, there is no cure available for these diseases. The best way is to cut off all the infected parts of the tree and dispose of them properly.


Diseases are common in trees just like they are to human beings; therefore, regularly checking the trees is essential. This is especially important to monitor their health. If you notice any changes or symptoms on your trees, immediately contact your local arborist or a professional tree service company for advice on dealing with the situation. The earlier you take action, the better. Early disease detection could save your trees!

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