Anthracnose: The Most Common Tree Disease Explained

Anthracnose: The Tree Disease You Have Probably Already Seen

If you have ever noticed brown, irregular blotches on tree leaves in spring, you have likely encountered anthracnose. It is the single most common foliar disease of hardwood trees across North America, and almost every shade tree species is susceptible to some form of it. The good news is that while anthracnose looks alarming, it is rarely fatal to otherwise healthy trees.

Anthracnose is caused by several different fungal species, each targeting specific host trees. The disease thrives in cool, wet spring weather — exactly the conditions that occur during leaf emergence in most of the United States.

Which Trees Get Anthracnose?

Nearly every deciduous hardwood can be affected, but the most commonly and severely impacted species include:

• Sycamore / London plane — often the most severely affected; can cause complete defoliation and twig dieback
• White oak and other oak species — brown blotches along leaf veins are characteristic
• Maple — irregular tan to brown spots and leaf distortion
• Dogwood — can cause serious flower and leaf damage, sometimes leading to canopy thinning
• Ash — brown spots and premature leaf drop, compounding stress from other issues
• Walnut, hickory, and elm — moderate susceptibility depending on weather conditions

Identifying Anthracnose

Use our diagnosis tool to compare symptoms on your trees with confirmed examples. Key signs include:

• Irregular brown or tan leaf spots that often follow veins or appear at leaf edges
• Leaf distortion — curling, cupping, or crinkling of leaves, especially in spring
• Premature leaf drop in severe cases, particularly on sycamores
• Twig dieback — dead shoot tips and small twigs with sunken, dark cankers
• "Witches' broom" clusters on sycamores, caused by repeated bud kill and regrowth

Anthracnose symptoms typically appear on the lower and interior canopy first, where humidity is highest and air circulation is poorest.

Why Anthracnose Occurs

The fungal spores that cause anthracnose overwinter on fallen leaves and dead twigs. In spring, rain splashes these spores onto emerging leaves and new growth. Infection is most severe when:

• Spring temperatures remain below 60 degrees Fahrenheit during leaf expansion
• Prolonged wet weather keeps foliage damp for extended periods
• Trees are in shaded, sheltered locations with poor air circulation

Warm, dry springs typically result in minimal anthracnose. This is why the severity varies dramatically from year to year.

Treatment and Management

For most trees, anthracnose management focuses on cultural practices rather than chemical treatments:

• Rake and dispose of fallen leaves in autumn to reduce the overwintering fungal inoculum
• Prune for air circulation — removing interior crossing branches improves airflow through the canopy
• Water and fertilize appropriately to maintain overall tree vigor
• Avoid overhead irrigation that keeps foliage wet for extended periods

Fungicide treatment is generally recommended only for high-value trees with a history of severe, repeated anthracnose infections. Treatments must be applied as a preventive — typically at bud break and again 10 to 14 days later. Once symptoms are visible, fungicides cannot cure existing infections.

Consult an ISA Certified Arborist if you have a high-value tree experiencing severe anthracnose year after year.

When to Worry

Anthracnose alone rarely kills a mature tree. However, repeated severe infections over multiple years can weaken trees and make them susceptible to secondary problems. Seek professional assessment if:

• Your tree is defoliated by anthracnose for three or more consecutive years
• You see significant twig and branch dieback in addition to leaf spots
• The tree shows overall decline in canopy density and growth

Frequently Asked Questions

Q: Will my tree recover from anthracnose defoliation? A: Yes. Most trees produce a second flush of leaves within a few weeks after anthracnose-related defoliation. These new leaves typically emerge when warmer, drier conditions have reduced infection pressure.

Q: Is anthracnose contagious between different tree species? A: The fungal species that cause anthracnose are generally host-specific. The anthracnose that infects your sycamore will not spread to your oak, and vice versa. Each tree species is attacked by its own specific anthracnose pathogen.

Q: Can I prevent anthracnose by keeping my tree healthy? A: A healthy tree tolerates anthracnose better, but even perfectly healthy trees can be severely infected during cool, wet springs. Good cultural care minimizes the impact but cannot prevent infection when weather conditions favor the fungus.

Q: Is the fruit from a tree with anthracnose safe to eat? A: Anthracnose fungi are plant pathogens and do not affect human health. Fruit from affected trees may have cosmetic blemishes but is safe to consume after washing.