Powdery Mildew vs Anthracnose: How to Tell the Difference
Learn to distinguish between powdery mildew and anthracnose, two common fungal diseases that affect the leaves of many tree and shrub species.
At a Glance
Powdery Mildew
LOW- Type
- Fungus
- Severity
- LOW
- Affected States
- 49 total (49 active)
Symptoms
White to gray powdery coating on upper leaf surfaces and young shoots, leaf curling and distortion, stunted new growth, premature leaf drop in severe cases
Anthracnose
MODERATE- Type
- Fungus
- Severity
- MODERATE
- Affected States
- 38 total (38 active)
Symptoms
Irregular brown or tan dead areas on leaves often following veins, distorted or curled leaves, premature defoliation, twig dieback and small cankers on branches
Similarities
What makes Powdery Mildew and Anthracnose easy to confuse:
- Both are common fungal diseases found throughout the United States
- Both primarily affect leaves and can cause premature leaf drop
- Both are favored by certain weather conditions during the growing season
- Both can affect a wide range of ornamental and shade trees
- Both are generally not fatal to otherwise healthy, mature trees
Key Differences
| Feature | Powdery Mildew | Anthracnose |
|---|---|---|
| Appearance | White to gray powdery coating on leaf surfaces | Brown or tan irregular lesions and blotches on leaves |
| Favored conditions | Warm days, cool nights, dry leaf surfaces, moderate humidity | Cool, wet spring weather with prolonged leaf wetness |
| Affected surface | Grows on top of leaf surface (epiphytic) | Causes lesions within leaf tissue |
| Affected species | Dogwood, lilac, rose, crape myrtle, sycamore, and many more | Oak, sycamore, maple, ash, dogwood, and others |
| Severity | Mostly cosmetic; rarely causes serious harm | Can cause significant defoliation in severe years |
| Treatment | Fungicides, improved air circulation, resistant varieties | Usually no treatment needed; fungicides for high-value trees |
How to Tell Them Apart
- Look for white powder: Powdery mildew is unmistakable as a white or grayish powdery film on leaf surfaces. Anthracnose never produces a powdery coating.
- Examine lesion type: Anthracnose creates brown or tan dead spots and blotches that may follow leaf veins. Powdery mildew starts as white patches that may eventually cause leaves to yellow or curl.
- Consider the weather: If symptoms appeared after a cool, wet spring, anthracnose is more likely. If the weather has been warm and moderately dry with cool nights, powdery mildew is favored.
- Rub the leaf surface: Powdery mildew can often be rubbed off the leaf with your finger, revealing the tissue beneath. Anthracnose lesions are embedded in the leaf tissue and cannot be wiped away.
- Check the time of year: Anthracnose is primarily a spring disease. Powdery mildew often appears in late summer and fall when conditions favor its development.
Frequently Asked Questions
Can a tree have both powdery mildew and anthracnose?
Yes, especially on susceptible species like dogwood and sycamore. Anthracnose may appear in spring, and powdery mildew may develop later in summer on the same tree in the same growing season.
Do I need to treat powdery mildew?
For mature landscape trees, treatment is usually unnecessary. Powdery mildew is largely cosmetic. For ornamental plants where appearance matters (roses, crape myrtles), fungicide sprays or resistant varieties are recommended.
Will anthracnose kill my sycamore tree?
Very rarely. Sycamores are notorious for heavy anthracnose in wet springs, often losing most of their initial leaves. However, they reliably produce a second flush of healthy foliage as temperatures warm. Repeated severe years can contribute to decline but alone are seldom fatal.
Are there resistant varieties available?
Yes for both. Many crape myrtle cultivars resist powdery mildew. London plane trees (a sycamore hybrid) are much more resistant to anthracnose than American sycamores. When planting new trees, selecting resistant cultivars is the best long-term strategy.
Is powdery mildew contagious between different plant species?
Generally no. Most powdery mildew fungi are host-specific, meaning the species that infects roses will not infect oaks. However, closely related plants may share the same powdery mildew species.