Have you noticed brown spots on the leaves of your Crabapple that appear to elongate as the season progresses? Did the brown-spotted leaves turn yellow and drop earlier than normal? Was your crabapple sparse with leaf cover and just not looking good in July? If these symptoms sound familiar, your tree could be infected with Apple Scab, which is one of the most serious fungal diseases that affect ornamental trees.
The Apple Scab fungus overwinters in bark crevices and on fallen infected leaves. In the spring, the fungus produces millions of spores. The spores are released in wet spring weather when the tree is in bloom and are carried by the wind to new leaves, fruit and twigs. The wetter the spring, the easier it is for the fungus to spread. Infection occurs under a wide range of temperatures, but wet plant surfaces are necessary. The severity of the infection increases when the humidity is high and temperatures are moderate.
Apple scab is a common fungal pathogen in areas that experience cool, wet spring weather. We take an integrated pest management approach when it comes to tree diseases and pests. We look at multiple influencing factors and treatment options prior to making final care recommendations for your trees. The factors and treatment options include preventative maintenance, mechanical enhancements, pathogen or pest pressure, sustainable treatments and routine monitoring services.
With apple scab, one step in controlling the pathogen is ensuring to remove fallen leaves and twigs each Fall which can help decrease the primary inoculum levels. Because of the ability of the spores to be readily dispersed, it is best to combine this preventative maintenance method with sustainable treatments. Unfortunately, there is no cure for Apple Scab, but control is possible through a combination of proper sanitation and sustainable treatments that are effective for controlling this disease. Control requires multiple applications done on a preventive basis, beginning in the Spring when leaf buds break and repeating applications until two weeks after flower petals fall.
Maintaining consistent watering methods during periods of drought and other preventative maintenance such as a mulch ring around trees in turfed areas, and cyclic pruning to maintain healthy air flow through the crown of the tree, you can keep apple scab at bay for your trees and our urban forest.
