The Most Common Tree Diseases in California

Keeping your trees in good health may require some time and energy. Of course, besides trimming, pruning, and fertilization, you may find yourself up against the most common tree diseases, too.

Why does your tree’s bark look discolored? Should you worry about the dark spots on your leaves? Below, Folsom’s reliable tree removal service, Ace Tree Service, shares a few tips from their ample experience with tree pests and diseases in California.

Fungal Tree Diseases


Anthracnose, a group of fungal diseases that affect various plants and trees, thrives in California’s warm, humid conditions. Susceptible trees include sycamore, maple, ash, and oak, which display the following symptoms of anthracnose:

  • Dark, sunken spots or lesions on affected leaves, flowers, fruits, and stems
  • Small yellow-brown spots that darken and spread 

While anthracnose may cause sectional shedding of leaves, it rarely overpowers or kills mature trees. Proper tree care from a knowledgeable arborist can keep this fungal tree disease in check.  

Dutch Elm Disease

Dutch elm disease is a fungal infection that has wiped out millions of elms since its accidental introduction to North America in the 1930s. The symptoms of infestation include the following:

  • Wilting
  • Yellowed leaves and branches
  • Leaves that curl and turn dark brown

Unfortunately, over time, the disease spreads to the rest of the tree, resulting in its death.   

Fusarium Wilt

The fusarium wilt fungus attacks crops such as tomatoes and bananas. The fungi spread easily, and, unlike some of the most common tree diseases, it can survive for a very long time in the soil. It doesn’t even need access to a living host, making it challenging to eradicate.  

Infection typically begins in the roots, where the fungus disrupts water transport. The disease causes older leaves to yellow, wilt, and die before spreading and killing the entire plant. No fungicide can control or cure fusarium wilt, so this pathogen nearly always kills an infected tree.

Bacteria and Mold-related Tree Diseases

Fire Blight 

A common and frequent bacterial disease, fire blight, will often show up with the tree’s active growth period in early spring. You’ll frequently see fire blight on California’s apple and pear trees. It spreads rapidly and causes significant damage.

Fire blight affects all parts of the tree, from flowers to leaves and branches. Typically, it turns everything dark brown or gives them a black scorched appearance, hence the name. 

Unfortunately, fire blight has no cure and may kill the tree without intervention from an arborist.

Sudden Oak Death  

Sudden oak death has taken out millions of oak trees and several other tree species since its first sighting in the 1990s. A water mold pathogen causes this tree disease and related plant diseases. 

With no known cure, preventing the movement of the disease from infected plants to others nearby is the only way to protect forests and landscaping.

Common Pests in California That Can Affect Trees

Since tree diseases make their host trees more susceptible to pests, it helps to stay alert for the following opportunistic insects:

  • Cabbage palm caterpillar  
  • Royal palm bugs  
  • Gold spotted oak borers  
  • Palmetto weevils  
  • Oak worms  

Trust Your Local Tree Experts for Healthier Trees

Ace Tree Service has established itself as a professional tree service with a solid reputation in California. We can handle all your tree care needs, big or small, including the following and more:

  • Tree trimming and pruning  
  • Tree removal and land clearing  
  • Defensible space clearing  
  • Emergency storm cleanup services

Have you noticed some black spots on tree leaves or other signs of California’s most common tree diseases? Don’t wait; call Ace Tree Service at (916) 934-3204 to request a free estimate for tree services in Folsom, CA, and the greater Sacramento area.