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As Spring Arrives

Apple Scab: A Fungal Disease

Apple Scab: A Common Fungus

Apple Scab-1

Apple and Crabapple trees are very popular across our region; however, without proper care they can become infested with unwanted apple scab, effectively devastating the leaves and fruit.

Apple scab is a fungus that can infect the leaves and fruit of both apple and crabapple trees, and also mountain ash and pear trees. Scab appears as a brown velvet-like lesion, and it thrives during the wet periods of the spring and summer. It needs to be treated during the growing season.

 

How does Apple Scab affect my Tree?

apple-scab-leaf

Apple scab will be more of a problem to susceptible crabapple cultivars. Once the tree is infected the leaves will eventually turn yellow and fall prematurely. Highly susceptible crabapple trees can lose a majority of their leaves by mid-summer. This will cause the tree to become much weaker. Apple scab does not kill your trees but it can greatly affect its aesthetics as well as the growth of the fruit and yes, crabapples are edible! In severe cases it can reduce or completely eliminate the fruit yield for an entire growing season.

The Disease Cycle

Apple scab overwinters on leaves that are infected that had been shed already. Once the rainy days start to come in spring, the spores then are expelled from the infected leaves and are moved around by air currents and splashes of rain where they can then start new infections. If the weather is favorable (rainy/moist) it can enable the leaf spots that are infected to mature and produce new fungal spore which will reach the nearby leaves and in turn spreading the disease. Excessive rainfall in the prime seasons (spring and summer) often results in the disease coming back again with more severity.

How to Manage Apple Scab

  • Proper care measures include pruning in the late winter or early spring to increase airflow and remove any infected areas; however, it is best to prune when conditions are dry. Pruning during wet periods can actually aid in the spreading of scab.
  • Raking and destroying the leaves as they fall should reduce the severity of the disease next season as the fungus overwinters on partially decayed leaves.
  • Topical fungicide applications are also recommended every year to help prevent infestation on susceptible trees. 
    • Chemical fungicides are used for two purposes:
      1. Preventative: Sprayed on the leaves and fruit prior to infection. This will help effectively prevent the fungal spores from germinating or penetrating the host.2. Curative: Applied shortly after infection can hinder the development of the fungus which will limit the progression of the disease.

Being aware of scab now will help you prevent it next season. If your apples and crabapples were not treated for scab this spring, we recommend inspecting them to see if scab has developed. If so, we recommend you take the proper care measures beginning next March or April in order to prevent apple scab.

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If you have any questions or concerns please don't hesitate to reach out to us at 877-308-8733! All estimates are free of charge. We look forward to hearing from you.

Editors Note: This post was originally published in July 2011 and has been revamped and updated for accuracy and comprehensiveness.

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