Though the redbud is not susceptible to a large number of diseases, it has poor resistance to the few diseases to which it is susceptible. The majority of the diseases that affect the redbud are not fatal. One is avoidable and another can be treated with fungicides while the third is likely fatal. Proper planting and care can help avoid the fungal infections which lead to the diseases common in redbud trees.
About the Redbud
The redbud is an ornamental shade tree, popular for its reddish-purple spring blooms that sprout all along its trunk and branches. It has a relatively low disease tolerance and life span compared to other ornamental trees, living only about 20 years. It is native to North America and thrives in planting zones 4b through 9a. It grows to between 20 and 30 feet in height with an average spread of 15 to 25 feet.
Verticillium wilt is common and severely damaging to shade trees, redbuds and maple trees in particular. Symptoms include a midsummer yellowing of leaf edges followed by browning and drying. Sudden wilting may affect a few branches or just one side of the tree. The wood beneath the bark of the affected branches will be discolored in streaks of chocolate brown. The intensity of the infection determines whether the tree will die in just one season or linger for several seasons. It is caused by a soil-born fungus called Verticillium albo-atrum and is absorbed into the plant through its water-conducting tissues in the root system.
Cankers are typically the result of an injury, frequently caused by pruning and avoidable. The opening allows fungus to gain access to the tree and cause the canker to develop. Cankers start as small, sunken spots on a branch that begin to girdle the branch. The infected wood begins to turn black and will split away from the non-infected wood. Once infected, there is no cure. The damaged branch should be removed.
Leaf spot is also a fungal disease and can be treated with fungicides. Leaf spot is not fatal and is scarcely more than a nuisance. Discolored dead spots appear on otherwise healthy leaves. A five-year study by Duke University released in 2009 showed that the incidence of leaf spot in redbuds increased in warm, humid conditions or when trees were exposed to elevated atmospheric CO2 concentrations.
The best treatment for disease in redbuds is prevention. Providing the proper location and climate for growth and careful maintenance practices will reduce risks of disease. Trees will do well in partial shade to full sun. Redbuds have a high drought tolerance and do well in clay, loam and sand, or sometimes in wet acidic or well-drained alkaline soils. Redbuds have few pest problems. Clean pruning cuts will help prevent fungal infections.