The red maple (Acer rubrum) is named for its showy red displays during every season. The winter brings red twigs and buds, spring brings red flowers and summer brings red leafstalks and twigs. The fall, however, is the red maple's true showcase; in this season, the tree produces vibrant red leaves of crimson or wine red. Red maples are particularly susceptible to a variety of fungal, bacterial and nutrient-deficiency diseases, including the often fatal verticillium wilt.
Verticillium wilt is caused by several species of soil fungi that invade susceptible plants via the roots. Over 300 cultivated plants are at risk, but maples are among the most susceptible trees. Verticillium dahliae is the species that most commonly infects woody plants in the United States. Verticillium wilt fungi produce toxins and invade the water-conducting tissues of plants, spreading upward through spores. In response to the fungus, trees produce gums in the infected vessels in an attempt to isolate the invaders. This reduces water and nutrient flow from the roots. Some trees will succeed in isolating the infection and recover; others will not.
Verticillium Wilt in Maples
Verticillium wilt fungus in maples establishes itself first in a single growth ring and then progresses from there. How much damage the infection does depends on how far it is able to travel through the wood and roots. If it reaches old-growth wood, the infection will likely be fatal. However, if it cannot progress past the first growth ring into other seasons' growth rings, the disease will go into remission and compartmentalise. If acute symptoms return after one or more years without signs of the infection, it is the result of a new infection and not a continuation of the previous one.
Acute and Chronic Symptoms
Chronic symptoms of verticillium wilt in maples is often slightly less troubling than acute, severe symptoms, as slow, chronic infections are less likely to cause sudden wilting and death. In chronic infections, red maple leaves grow poorly, turn yellow and show signs like leaf scorch, abnormally heavy seed production and the dieback of shoots and branches. Foliage can suddenly wilt and die. Acute infections are often more severe, producing leaf curling and drying, abnormally red or yellow leaves, partial defoliation, wilting of leaves and branches in an entire section of a tree and a sudden dieback of infected sections. The most severe acute infections can rapidly cause wilting, dieback and total tree death.
Other Causes of Wilting
While verticillium wilt is often the first and most likely suspect in red maple wilting, other causes can mimic some symptoms of verticillium wilt. Maples are weakened by adverse environmental conditions and are susceptible to herbicide and mechanical damage. Herbicide damage can cause leaf distortion and death. Maples are also prone to mechanical damage, providing an opening for a variety of pests and diseases that can cause leaf damage. Verticillium wilt, however, will cause streaking in the wood similar to Dutch elm disease. Evaluate the tree carefully for the entire scope of symptoms.
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- North Dakota State University Agriculture Department: Deciduous Tree Diseases: Maple
- North Dakota State University Agriculture Department: Deciduous Tree Diseases: Parasitic Diseases of Widespread Occurence
- University of Minnesota Extension; Verticillium Wilt of Trees and Shrubs; Cynthia L. Ash;
- Clemson University Cooperative Extension: Red Maple
- Clemson University Cooperative Extension; Maple; Debbie Shaughnessy; November 2006