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Hoppe Tree Disease Alert: Apple Scab

Written by John Sepulveda, Certified Arborist WI-1454A, and Cory Tucek, Certified Arborist WI-1234A

Apple scab is a disease caused by the fungus Venturia inaequalis. Wet and cool conditions during the spring months make this fungus more prevalent. Trees within the rose family are affected by this fungus, including apple trees and crab apples. It also affects hawthorn, mountain ash, and pear trees. Apple scab is found worldwide, and is the leading cause of economic loss of apple crops in North and South America, Europe, and Asia.

Recognizing Apple Scab

Crab apples are popular within our landscape due to their aesthetic values they provide such as

flowers, wildlife habitat, and usually smaller structure. When a tree becomes infected with the apple scab fungus, early defoliation reduces the trees photosynthesis capabilities. Lesions caused by apple scab can be seen at first on the tops of leaves. They are circular with feathered looked edges. They are often an olive green to black color and start small but can grow to half an inch in size. The fungus will also infect the fruit of these trees, making them less aesthetically pleasing and can cause a lower fruit yield. The fungus is not deadly to the tree, but it can cause early defoliation and make the plant more susceptible to secondary pests or diseases. It causes additional stress year after year which often leads to branch dieback.

Apple Scab Treatment and Prevention

The first step to reducing the apple scab fungus is to clean up and destroy all leaves that drop in the late summer/fall months before our winter snows begin. The fungus will survive on the leaves over the winter and then produce/release these spores in the spring through wind and rain.

Hoppe Tree Service can also help deter this fungus with proper pruning and/or fungicide treatments. A proper pruning will help increase airflow throughout the canopy thus drying the leaves faster and making it harder for the fungus to spread. This airflow will also help push fungal spores out of the canopy.

Fungicide treatments are another option for deterring the initial infection. Treatments on crab apples should occur two to three times in the growing season when the fungus is most prevalent. Edible fruit trees will need additional treatments to help reduce other fungal and insect issues. The treatments help the tree hold its leaves throughout the entire growing season, improving the tree’s photosynthesis capabilities and allow it to store ample water and nutrients for the following growing season. High micro-nutrient fertilization can also help improve the trees overall health, vigor, and appearance.

A treated for apple scab keeps its leaves through the autumn season.

Selecting a Disease-Resistant Tree

Disease resistant trees have been heavily researched in labs and nurseries. Many newer crab apple cultivars have a higher disease resistance to the apple scab fungus and fire blight bacteria. In addition, site conditions should still be considered when planting new trees. Crab apples do best in full sunlight where it is warmer and less wet, which will help reduce fungal issues.

Hoppe is a full-circle tree care company that can diagnose and treat apple scab with pruning, foliar fungicide sprays, and micro-nutrient fertilization. Homeowners often notice an immediate improvement in the leaves and fruit of their trees after treatment. We also can help you select and plant the right apple and crabapple trees for your yard. If you have concerns about apple scab on your trees or are thinking about having a new tree planted, give us a call. A member of our team of certified arborists will be happy to visit your yard and inspect your trees.

Since 1972, Hoppe Tree Service has been taking care of people and their trees. Join us as we celebrate 50 years of service to great customers in southeastern Wisconsin.

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