Managing Anthracnose in Wet Springs
While the Treasure Valley is technically classified as an arid, high desert steppe climate, we occasionally experience anomalous spring weather patterns characterized by prolonged cool temperatures and unusually heavy rains. While this extra moisture is fantastic for filling our local reservoirs, it creates the perfect incubation environment for a stubborn and unsightly fungal disease known as anthracnose. If you have ever noticed early leaf drop or ugly, distorted brown spotting on your shade trees in late May or June, anthracnose is the likely culprit.
The Biology of the Fungal Pathogen
Anthracnose is not a single disease, but rather a general term for a group of closely related fungal pathogens that attack the foliage, buds, and twigs of deciduous trees. In our area, it most commonly affects sycamores, maples, ash trees, and certain species of oaks.
The life cycle of this fungus is directly tied to the weather. The fungal spores survive the harsh winter by laying dormant in fallen leaves on the ground, or within small, dead twigs in the tree’s canopy. When the spring rains arrive, the physical splashing of water droplets carries and spreads the microscopic spores up onto the newly forming, highly vulnerable green foliage. If the weather remains cool and wet, the fungus rapidly colonizes the leaf tissue.
Identifying the Infection
To a homeowner, a severe anthracnose infection looks terrifying—as if the tree is suddenly dying overnight. The visual symptoms include:
Fortunately, while this aesthetic damage looks alarming, a healthy, mature tree possesses a remarkable ability to compartmentalize the damage. Once the hot, dry Idaho summer weather arrives in late June, the environmental conditions are no longer suitable for the fungus. The disease stops spreading, and the tree will typically push out a second, healthy flush of leaves.
Proactive Management and Plant Health Care
Managing this fungal pathogen relies heavily on preventative cultural practices and a Plant Health Care (PHC) approach.
Structural Thinning: Properly pruning the tree in accordance with ANSI A300 standards to increase canopy airflow and sunlight penetration allows the leaves to dry out much faster after a rainstorm. This removes the prolonged moisture the fungus requires to breed.
Sanitation: Raking up and disposing of fallen, infected leaves in the autumn prevents the spores from successfully overwintering at the base of the tree.
Targeted Fungicide: For highly susceptible trees, or trees already stressed by construction damage or drought, preventative fungicide sprays applied exactly as the buds open in the spring can protect the new foliage from initial spore dissemination.
If your trees are suffering from early leaf drop or recurring fungal issues, proper diagnosis is the first step toward recovery. Reach out to Arborman Tree Care at 208.286.6875 or visit arbormantreecare.net for a professional canopy assessment.
