Oak anthracnose is a foliar fungal disease, Apiognomonia quercina, that causes darkened spots and lesions on infected leaves. Although unsightly, anthracnose is rarely harmful to the tree’s health, however if infection is severe repeated defoliation can reduce the tree’s resources, leaving it more susceptible to insect attack. Anthracnose spores are activated by cool wet spring weather, so predicting symptoms from year to year can be difficult.
Susceptible Hosts
Several species including:
- Oak (Quercus)
- Maple (Acer)
- Ash (Fraxinus)
- Dogwood (Cornus)
Signs of Damage
- Distorted areas on leaves and irregular patches of leaf discoloration and necrosis.
- Early leaf drop.
- Blotches along leaf veins.
- Shoot and leaf blight, twig, and branch cankers.
- Defoliation usually occurs from bottom of canopy spreading to upper canopy.
Physical Appearance
- Dark lesions/spots on leaves.
- Velvety appearance of leaf spots is the result of spore production on the leaf surface but most of the signs will be microscopic.
Biology / Lifecycle
- The pathogen overwinters in infected leaves on the ground from the previous year or on the tree in crevices on the buds, twigs, and bark.
- In spring, overwintered spores (ascospores) mature and are discharged over a period of 5 to 9 weeks.
- Wind and splashing rain carry spores from infected leaves to new growth on nearby trees where new infections begin.
- In late summer or early fall the primary infections produce secondary spores and create new infections, which can continue through the growing season during wet periods.
Black leaf spots on Ash (Fraxinus)
Typical bottom up defoliation
Black lesions on Maple (Acer)
Treatment Strategy/Expectations
The need for fungicides depends on the susceptibility of the species and weather conditions. Since most anthracnose fungi are dependent on wet weather, fungicide applications may be needed for control during wet seasons. Fungicide applications are preventive only and need to be timed properly for effective control.
Cultural treatments (e.g. root collar excavation, proper irrigation, soil management, etc.) need to be considered to improve/maintain plant health.
| Product | App. Method | Dosage | Timing | Re-Treatment |
| Foliar spray | 4-6 oz/100 gallons water | Apply at bud break | 2-3 times on 14-day intervals | |
| Foliar spray | 1 3/8 pints/100 gallon water | Apply at bud break | 2-3 times on 14-day intervals | |
| Foliar spray | 20 fl oz/100 gallon water | Apply at bud break | 2-3 times on 14-day intervals | |
| Soil drench or soil injection | Refer to Cambistat rate card | Whenever the ground is not frozen or saturated with water. | Every three years |
*Product is Rainbow Ecoscience’s industry standard recommendation for most industry situations.
**Cambistat is a plant growth regulator that induces a disease resistance response in trees.
Reach out to Rainbow Ecoscience Technical Support for additional protocol support.
Foliar spray with Maruyama
Soil application with HTI 2000
Always refer to product label for rates and approved uses. Some images courtesy of forestryimages.org or Wikimedia Commons. Use of the images does not imply endorsement of treatments.
