Apple Scab & Rust-Common Diseases In Portland

Serving Families Throughout Portland & the Pacific Northwest

Our mild climate is great for growing a wide variety of trees and shrubs.  Unfortunately, that same reason is precisely why Portlanders can also face an ongoing battle with disease in their plants, shrubs, and trees.

Spotting disease early

Pathogens are everywhere.  Since we have weather conducive to disease growth, it’s no surprise that if you have a plant or tree susceptible to a disease, you will likely see symptoms of that disease.

The key is keeping your trees and plants healthy so they are better able to fight off these pathogens. Also, spotting disease symptoms early is best as treatment will be more effective.


With so many apple trees around, it makes sense that Apple scab is a big problem around here. In addition to affecting fruit apple and crabapple trees, it can also be an issue for mountain ash, pyracantha, cotoneaster and common pear.


  • Small olive-green infection spots on leaves that grow larger to become (more or less) circular.
  • Leaves may be curled or puckered.
  • Leaf drop occurs, which weakens the tree.
  • Fruit develops brown-black spots that enlarge to become (more or less) circular and makes the fruit unmarketable.
  • Infected areas become raised and look like a scab (hence the name).
  • On succulent growth, bumps occur and over time, they become cracked and rough.


Rust infections are common in many varieties of trees, including apple trees. Usually caused by the fungi Gymnosporangium or Melampsora, it can cause serious damage including defoliation and death of any fruit on the tree.  Controlling the disease requires equal parts of cultivation and chemical control.


While symptoms can vary among tree varieties, you’ll usually see signs in both the leaves and bark.  Leaves will develop yellow spots that grow and eventually, turn orange (like rust). Orange, gelatinous horns called galls will appear on branches.


There is no cure as all pathogens cannot be eradicated from the environment therefore, treatment is not a “one and done” procedure.  Repeated treatments are needed to keep the disease symptoms in check.

The good news is that General Tree has treatment plans for common diseases plaguing Portland homeowners. Of course, there are preventative measures you can put in place to reduce disease symptoms.

In addition to treatment, our experts offer tips for reducing symptoms, such as keeping your landscape clean by removing fallen leaves/twigs or having trees and shrubs properly pruned on a regular basis.

Contact General Tree Service for more information about our insect and disease control treatments. Our goal is to keep trees and plants in Portland metro, Salem and Yamhill Counties and SW Washington healthy and looking great.

The post Apple Scab & Rust-Common Diseases In Portland appeared first on General Tree Service.

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