Servicing Harford County, Baltimore County & Baltimore City

Common Forms of Tree Disease

Common Forms of Tree Disease

The best way to cure a tree ailing from tree disease is to recognize common tree diseases.

A tree might not immediately come to mind when you think of diseases. However, trees are organisms that can become susceptible to diseases, just like people or pets. The best way to cure a tree ailing from tree disease is to recognize common tree diseases. We’re here to help you learn about common illnesses and help you care for your trees and keep them in top condition. Here are five common forms of tree disease.


Tree fungi cause rust diseases that typically take place in late August. The following hardwood and fruit-bearing species are especially vulnerable to rust: 

  • Oaks
  • Birches
  • Maples
  • Cottonwood
  • Poplars 
  • Quince
  • Crabapple
  • Pear
  • Hawthorn

Red cedars like Eastern red cedar are also vulnerable to rust. Identify tree disease by looking for twig galls or cankers on cedar trees. You might also see reddish-orange fungal spores on infected twigs. Treat rust by removing any visible galls from trees before April. It’s also best to plant vulnerable fruit trees far apart so that possible infection doesn’t spread. 

Rotting Roots 

A fungal infection causes tree root rot. Root rot affects trees in wet or infected soil or with damaged stems or roots. Newer trees may develop root rot if the decay in the ground stems from previous infestations. Older plants might fall susceptible to root rot if water drainage patterns change. 

Forest trees or trees planted in heavy, wet soil are especially vulnerable to rotting roots. You might see spongy wood or wood oozing with sap at the tree’s base. Other symptoms include the following: 

  • Insufficient growth
  • Loss of needles
  • Discolored needles that turn brown or light yellow
  • Blemished wood at the bottom of the stem
  • Dark brown threads at the bottom of the stem
  • Dead lower bark loosening and separating

Root rot isn’t curable, nor can you extract the fungi from the soil. Instead, you can prevent root rot by planting trees away from the ground with poor drainage, downspouts, or other areas where water collects. 

Black Knot

Tree fungi that create galls and black swelling on trees and shrubs cause black knots. The fungus contaminates new branches in late spring and early summer in damp weather and releases spores from the galls. Black knot affects fruit trees such as: 

  • Plum
  • Cherry
  • Flowering almond
  • Apricot 
  • Blackthorn 

During the first year, trees with this tree disease develop brown swellings that might appear on the trunk or branches. Then, during the second year, these swellings surround the stem and form black galls, causing the tree’s surface to crack or split. 

A severe black knot infection is powerful enough to kill a tree if the galls surround the trunks or large limbs. The best way to prevent this common tree disease is to prune any infected stems or branches in early spring. 

Bacterial Leaf Scorch

Bacterial leaf scorch stems from bacteria getting inside plants’ vascular tissues. This bacteria can spread and block water moving from trees to branches. Bacterial leaf scorch affects the following tree species: 

  • Elm
  • Oak
  • Maple
  • Gingko
  • Sycamore

If your tree has bacterial leaf scorch, you’ll see uneven browning on its leaves every year from mid to late summer. The browning could progress from lower to higher branches, with some tree species having a yellow halo or “scorch” around them in diseased areas. 

This tree disease isn’t curable. However, you can prune dead wood and infected branches. 

Powdery Mildew

The last common tree illness we’d like to discuss is powdery mildew. This mildew grows on the tree leaves, stems, shoot tips, and flower buds of an infected tree. Tree fungi cause powdery mildew, and you can identify it by its white spots that look like talcum powder. 

Young plants that grow in the shade are highly susceptible to powdery mildew. Powdery mildew also spreads during warm days and humid, cool nights. Fungi spread through air currents from plant to plant during the day and absorb moisture to spread at night. Powdery mildew can infect a tree during the growing season, stay in the leaves during the winter, and move to new plants the following spring. 

Powdery mildew won’t kill a tree. However, mildew is an eyesore that causes leaves to become discolored and distorted. Plus, this mildew blocks plants from receiving enough light. Prevent this issue by growing mildew-resistant varieties, ensuring they have enough space for sunlight and air circulation.  

Professional Tree Service from Harford Tree

Ready to have the beautiful yard you have always dreamed of? Harford Tree Experts & Landscaping, Inc has been in the business for decades, providing customers with quality work and quick responses all at the right price. We service the areas of Harford County, Baltimore County, Baltimore City areas including Bel Air, Fallston, Perry Hall, Towson, Essex, Parkville, White Marsh, and Middle River. For service during business hours, reach out to us or give us a call at 410-592-7321. We offer 24/7 emergency service as well, just give us a call at 443-250-6649. For updates about our business and more informative tips, follow us on Facebook and Twitter.

This entry was posted on Thursday, January 5th, 2023 at 10:16 am. Both comments and pings are currently closed.

Comments are closed.

Quick Contact Form