If your climate has been dry and hot for more than two weeks and your maple tree is showing a gradual decline in health, the maple tree may be infected with charcoal root rot. Unlike many root rot diseases, your maple tree will not develop conks, lesions or cankers. However, the effects of charcoal root rot are deadly to the maple tree.
Charcoal Root Rot
Though commonly known for its damaging effects on the soybean, charcoal root rot targets more than 300 species throughout the world. This soil-borne fungal disease is rampant during hot, dry weather but can also infect trees in humid climates. Infecting maple trees through the root system, this disease causes the gradual molecular breakdown of the roots. This leads to the root system's inability to pass nutrients and water throughout the system. Upon inspection, the root system generally shows no damaging signs of infection. However, the infected roots will appear to be covered in a dust of black charcoal.
The Aceraceae, or Acer, family consists of 120 maple trees and shrubs that originate from locations throughout the world. The heights of these deciduous trees range low-growing up to 120 feet. These temperate and hardy trees produce rich green foliage that change to showy hues of red and gold in the fall. Maple trees thrive in nutrient rich, well-drained soils and require ample irrigation for successful growth. Commercially, they are categorized into hard and soft maples. The U.S. Department of Agriculture explains that hardwoods are more resistant to shock, stronger and heavier than soft maples. In comparison, soft maple trees are lighter and have wider sapwood.
Maple trees that are infected with charcoal root rot will experience a gradual decline in vigor. The decline of the tree begins at the base of the tree and works its way up to the crown. The trunk of the maple tree is weakened. The branches and stems will experience die-back and growth stunt, and the foliage of the tree experiences premature defoliation. This pattern of decline continues until the tree is overwhelmed and eventually killed by the disease. The symptoms of infection are quite similar to fusarium and verticillium wilt, which are also soil-borne diseases.
Prevention is the only control for charcoal root rot. There is no cure or effective fungicidal treatment for this disease. Fumiganting the planting area before planting the maple tree can reduce the potential of charcoal root rot infection. However, it does not eliminate the potential. Vigorously growing maple trees are also more resistant to this infection than stressed maple trees.
Charcoal root rot is a considered as a dry-weather disease. It is most rampant within trees that are poorly irrigated and stressed due to dehydration. Therefore, it is important to keep your maple tree properly irrigated. Mulching the tree's planting area is also effective as it protects the temperature of the soil and maintains consistent soil moisture.