Diagnostic Double-Take: Scorch or Scab

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  Last Friday, outside our bank in Orrville, Ohio, I espied a crabapple tree with a carpet of brown leaves underneath the tree. On first glance, I imagined this to be due to leaf scorch and then leaf drop due to recent dry weather. After all, we are almost eight inches below normal over the past three months in many northeast Ohio areas. Made sense. I was simply following Question #4 of the 20 Questions of Plant Diagnostics: What Do You See That Looks Abnormal?

  Looking more closely, however, (Question #6 is: “Exactly What Do You See?)”, I noticed that there were many leaves, going from green to yellow to brown on the tree due to apple scab disease, caused by the fungus Venturia inaequalis. In fact, the brown leaves on the ground also had apple scab lesions and fungal colonies.


Apple scab on crabapple leaves


Scabby leaves on the ground


  Here is what I think happened. We did have wet spring conditions until early May. There was a good bit of scab as the “environment conducive to this disease” is wet, spring conditions. At that time many leaves became infected and eventually fell to the ground, and at a slower rate they are joined by their co-horts affected by scab. Scab did not cause serious ornamental unsightliness overall, partly because secondary infections by the scab fungus were not encouraged due to drier conditions post-early May.


Crabapple tree with moderate scab


Scab, nor scorch. We could use some rain, though!