Yes! And quite easily, depending on the infection. Diseases, fungi, and pests can move from one tree to another if left unchecked. In areas like Nassau and Suffolk County, and NYC, where trees are often planted close together, this is especially important. Here’s how:
How Tree Diseases Spread
Tree diseases follow paths to spread biologically. Here’s how a sick tree spreading disease can impact its neighbors:
| How Disease Travels | How It Works | Common Pathogens/Diseases |
| Airborne Transmission | Fungal and bacterial pathogens release spores (tiny, microscopic seeds that are produced by fungi, bacteria, and some plants to help them reproduce and spread) into the air, which can travel via wind or rain splash. When they land on leaves, bark, or branches of healthy trees, they start new infections. | Fungal leaf spots, powdery mildew, rusts |
| Root-to-Root Contact | Pathogens move through the soil. If the roots of a sick tree are close to nearby trees, the disease can infect healthy roots. | Verticillium wilt, root rot fungi |
| Insect Carriers | Pests like beetles, aphids, and borers feed on infected trees and then move to healthy trees, carrying bacteria or fungi with them. | Dutch elm disease (via bark beetles), oak wilt, bacterial infections |
| Contaminated Tools | Tools like pruning shears, saws, or shovels can carry pathogens from an infected tree to a healthy one if not properly cleaned between uses. | Various fungal and bacterial infections, cankers |
Keep scrolling to find a more detailed chart on common tree diseases in New York City and how they spread.
Common Signs Your Tree Might Be Infected With Disease
Catching a disease early is critical. Look for:
- Leaf Changes: Yellowing, browning, wilting, or early leaf drop can all indicate stress or infection in your trees.
- Trunk or Branch Abnormalities: Cankers (sunken areas of dead bark), cracks, or sap oozing are warning signs. Fungal growths or mushrooms near the base often indicate root rot.
- Unusual Growth Patterns: Stunted growth, twisted branches, or bare patches in the canopy may point to disease.
- Dieback: Sections of branches or the top of the tree dying back suggest the tree’s vascular system is compromised.
If you notice these symptoms and realize it might be too late to save, call us to safely cut down your tree.
Protecting Nearby Trees From Disease
Help with the spreading of tree disease using these methods:
Maintain Healthy Trees
A healthy tree is more resistant to disease because it has stronger defences, more energy to heal, and can better withstand stress, though it’s not completely immune. Water during dry spells, apply mulch to retain moisture, and fertilize appropriately. Like always, take good care of your tree, as healthy trees are naturally more resistant to infection.
Isolate or Treat the Infected Tree
Removing infected branches, applying recommended treatments, or, in severe cases, isolating the tree can limit disease spread. Isolating a tree means separating it from healthy trees to prevent disease from spreading. Here’s how it can be done:
- Physical Distance: If possible, keep infected trees away from healthy ones by creating space, this is easier in larger yards or parks.
- Barriers: Use plastic sheeting, fencing, or temporary root barriers to block soil or water movement that could carry pathogens.
- Avoid Contact: Don’t let people, pets, or equipment touch the infected tree and then healthy trees without cleaning tools or hands.
- Prune Carefully: Remove diseased branches and dispose of them away from healthy trees to reduce airborne or insect-carried pathogens.
Sanitize Tools
Always clean pruning tools, saws, and shovels with rubbing alcohol or a bleach solution when switching between trees. With alcohol, you can wipe down the tools in between uses and let them air-dry for 30 seconds. It doesn’t need to be rinsed off since it evaporates.
To make the bleach solution, combine 1 part household bleach with 9 parts water (i.e. 1 cup bleach + 9 cups water). Dip or wipe the solution on the tools and let them sit for at least 30 seconds. After, rinse with clean water to prevent corrosion.
Monitor Closely
Check neighbouring trees frequently for early signs of infection so you can act quickly with the solutions we mentioned above!
A sick tree spreading disease can really mess with your other trees. Spotting it early, taking quick action, and keeping an eye on your yard can actually save a tree (or twos) life!
Common Tree Diseases in New York City & How They Spread
| Disease/Pest | How It Spreads | Typical Trees Affected |
| Emerald Ash Borer | Adult beetles fly to healthy ash trees and lay eggs. Larvae tunnelling under bark, disrupting nutrient flow. | Ash trees |
| Verticillium Wilt | Soil-borne fungi enter roots or wounds, then move through the tree’s vascular system. | Maples, elms, ash, dogwood |
| Fire Blight | Bacteria spread by rain, wind, insects, or contaminated tools. Infect blossoms, shoots, and branches. | Apple, pear, crabapple, hawthorn |
| Apple Scab | Fungal spores overwinter in fallen leaves, then splash onto leaves and fruit in spring rain. | Apple and crabapple trees |
| Magnolia Scale | Insects feed on the sap of infected branches, lay eggs, and spread via wind or movement of infested plant material. | Magnolia trees |
| Spider Mite | Tiny mites crawl or are carried by the wind to feed on leaves, sucking out plant fluids. | Maples, oaks, evergreens, and ornamentals |
| Aphid | Insects feed on sap, reproduce quickly, and move to nearby trees. They can carry viruses. | Many ornamental and fruit trees |
| Scale | Insects attach to branches and leaves. Spread by crawling, wind, or animals. | Maples, magnolias, citrus, and ornamentals |
| Leaf Miner | Larvae tunnel inside leaves, then exit to pupate and spread to nearby leaves. | Maples, birches, oaks, fruit trees |
| Dutch Elm Disease | Fungi are carried by bark beetles or spread through root grafts between trees. | Elm trees |