Anthracnose

Anthracnose is a general term for a group of fungal leaf and twig diseases caused by several genera — Apiognomonia, Discula, Colletotrichum, Gloeosporium — each with host preferences. The same word covers a cosmetic spring leaf drop on a mature sycamore (a non-event for the tree) and a near-certain death sentence on a flowering dogwood. The single most important call you make in the field is which one you're looking at.

Quick Start

• Anthracnose is host-specific — the fungus on a sycamore is not the fungus on a dogwood.
• Sycamore anthracnose is largely cosmetic on mature trees. Annoying spring defoliation; full refoliation by midsummer.
• Dogwood anthracnose can kill mature flowering dogwoods. Aggressive treatment or replacement is the call.
• Cool, wet springs drive infections. Outbreaks track the weather, not the calendar.
• Sanitation (remove fallen infected leaves) is the single highest-leverage cultural control.

Identification

Common across hosts:

• Irregular brown to tan lesions on leaves, often following the veins. Lesion edges are typically angular rather than round.
• Defoliation in spring, especially in cool wet seasons. Trees often refoliate by midsummer if otherwise healthy.
• Twig dieback in more aggressive cases — small branch tips die back from the terminal bud.
• Cankers on twigs and small branches in some species, particularly dogwood and sycamore.

The lesion pattern, host species, season, and weather context together are usually enough for a working field diagnosis. Lab confirmation is recommended for dogwood given the prognosis.

Host-specific patterns

Sycamore anthracnose (Apiognomonia veneta)

Affects American sycamore, London plane (less severely), and Oriental plane.

• Spring symptoms — entire developing leaves blacken and die; severe defoliation that looks alarming to clients.
• Midsummer recovery — healthy mature sycamores refoliate completely by late June or July with normal-looking leaves.
• Twig and bud cankers — small dead twigs throughout the canopy; characteristic "witches' broom" appearance over years from repeated terminal bud kill and lateral compensation.
• Long-term effect on otherwise healthy mature trees: cosmetic and structural (irregular crown shape), not life-threatening.

The annual variability is high. A wet cool spring produces dramatic defoliation; a dry spring produces almost no symptoms. Clients see the bad years and panic.

Dogwood anthracnose (Discula destructiva)

Affects flowering dogwood (Cornus florida) and Pacific dogwood (Cornus nuttallii) — both native species. Introduced pathogen, first identified in the 1970s, now widespread in the eastern US.

• Lower-canopy symptoms first — leaf spots and twig dieback start in the shaded lower branches, progress upward.
• Tan to purple-bordered leaf lesions with a darker center; often expand to blight whole leaves.
• Twig and trunk cankers — sunken dark cankers on twigs and main stems. Trunk cankers are the failure point: once they girdle the main stem, the tree dies.
• Epicormic sprouts — the tree responds to canopy loss with water sprouts; these are also susceptible and rarely persist.
• Mortality — established infections in shaded, humid sites often kill mature trees within 2-5 years. Trees in open, sunny, well-drained sites fare significantly better.

Oak, maple, ash anthracnose

• Oak anthracnose (Apiognomonia quercina) — leaf blotches along veins, occasional spring defoliation. Cosmetic on healthy oaks.
• Maple anthracnose (Aureobasidium apocryptum, Discula campestris) — similar pattern; cosmetic.
• Ash anthracnose — relevant historically; with EAB taking out most ash, anthracnose is rarely the defining issue.

For these hosts, the management answer is almost always "monitor; sanitation if accessible; no fungicide."

Diagnostic procedure

1. Identify the host species

   Anthracnose management is host-specific. Confirm whether you're looking at sycamore, dogwood, oak, maple, or another host before going further.

2. Check the symptom pattern against the host

   Vein-following lesions in spring on a sycamore + cool wet weather = sycamore anthracnose. Lower-canopy dieback on a dogwood with twig cankers = dogwood anthracnose. Match the pattern to the host before recommending action.

3. Assess severity and recovery history

   On sycamores especially, ask the owner if the tree has done this before and recovered. Repeated annual defoliation followed by midsummer refoliation is the normal sycamore-anthracnose pattern and does not require intervention.

4. Submit a sample for dogwood cases

   For dogwood with suspected anthracnose, lab confirmation is worth the cost — the treatment commitment and replacement decision both hinge on it. Submit symptomatic leaves and a twig with visible canker.

5. Assess the site

   Shade, humidity, airflow, and drainage all drive anthracnose severity. A dogwood in a humid shaded yard with poor airflow has a much worse prognosis than the same tree in an open sunny site, and that affects the recommendation.

Treatment options

| Host | Recommended action | Justification | |---|---|---| | Sycamore (mature) | Sanitation only; rake and remove fallen leaves in fall | Fungicide protection rarely cost-justified for landscape sycamores | | Sycamore (young or specimen) | Optional protective fungicide at bud break (chlorothalonil or copper) | Reduces cosmetic impact in years with high client visibility | | Dogwood (early infection) | Aggressive sanitation + protective fungicide (chlorothalonil, propiconazole, mancozeb) on a 7-14 day schedule starting at bud break | Best chance of long-term survival | | Dogwood (advanced, >50% canopy loss with active cankers) | Manage decline; plan replacement with resistant cultivar | Treatment will not reverse trunk cankers | | Oak / maple / ash (cosmetic) | Sanitation if practical; no fungicide | Cost not justified |

Cultural and site interventions matter more than chemistry for long-term anthracnose management:

• Airflow — selective pruning to open the canopy, especially on dogwoods.
• Avoid overhead irrigation — wet leaves drive infection. Drip irrigation or early-morning watering only.
• Mulch correctly — 3-4 inches of organic mulch over the root zone, pulled back from the trunk. No volcano mulch. Reduces root stress, which reduces susceptibility.
• Don't water-stress — drought-stressed trees are more susceptible to opportunistic infection.

Replacement cultivars (dogwood)

When a flowering dogwood is past saving, replacement options with better disease resistance:

• Stellar series (Rutgers hybrids of Cornus florida × C. kousa) — Aurora, Constellation, Ruth Ellen, Stellar Pink, Celestial. Good resistance to dogwood anthracnose.
• Cornus kousa (Kousa dogwood) — generally resistant; different bloom time and habit.
• Cornus mas (Cornelian cherry) — resistant; very different aesthetic, early yellow blooms.

Native-purist clients sometimes resist non-native replacements. The honest tradeoff: a Stellar hybrid will be alive in 20 years; a replanted Cornus florida in the same shaded humid yard probably won't be.

When to recommend removal

• Sycamore — anthracnose alone is rarely a removal indication. Combined with significant decay or structural defects, fold into a TRAQ-driven decision.
• Dogwood with >50% canopy loss + active trunk cankers — recovery prospects are poor; recommend removal and replacement with a resistant cultivar. Monitor and manage decline if owner prefers to keep the tree for sentimental value.
• Other hosts — anthracnose is essentially never the sole removal driver.

Common Questions

My sycamore loses all its leaves every spring — is it dying? Almost certainly not. Mature American sycamores tolerate repeated spring defoliation from anthracnose and refoliate by midsummer. Recommend sanitation (rake and remove fallen leaves to reduce inoculum) and reassure the client that the tree will leaf out again. The visual alarm is the worst part.

Is anthracnose the same as fire blight or bacterial leaf scorch? No. Fire blight is bacterial (Erwinia amylovora) on rosaceous hosts (apple, pear, hawthorn). Bacterial leaf scorch is xylem-limited bacteria producing chronic marginal scorch. Anthracnose is a fungal leaf disease with the lesion patterns described above. Misdiagnosis between these matters because the treatments are entirely different.

Should I prune anthracnose-infected dogwoods? Yes, with care. Prune in dry weather to open airflow and remove visibly cankered twigs back to healthy wood. Disinfect tools between cuts (10% bleach or 70% alcohol). Avoid heavy pruning on stressed trees — combine with a fungicide schedule and sanitation rather than relying on pruning alone.

Does Tree Inventory AI distinguish sycamore anthracnose from dogwood anthracnose in photos? Not specifically. The AI flags general decline indicators (defoliation, twig dieback, lesion patterns) and you confirm the species identification + diagnosis. Use the notes field on the tree detail to record the specific pathogen suspected and the recommended action; the PDF report carries this through to the client.

Related

• Oak Wilt — different vascular wilt pattern; useful contrast for diagnosing oak decline
• Pruning Best Practices — sanitation pruning guidance for infected trees
• Hazard Rating with TRAQ — framework for combining anthracnose with structural defects in a removal recommendation