More Abnormalities on Oaks

See Richard Jauron’s Yard & Garden news release (above) for a description of Botryosphaeria twig canker, oak apples and nutrient deficiency on oak trees.

Below is another look at an oak apple gall that fell on my driveway from a red oak tree.  Oak apples are attached to the leaf veins and formed early in the growing season as the affected leaf was developing.  Note the fibrous matrix inside the gall in the second photo.  Oak apples vary from 1/2 to almost 2 inches in diameter.  Early in the year, the gall will be spongy and green.  By fall, the galls become brown and brittle.

For an excellent pictorial review of oak apples, see Oak Apple Wasp Galls Bug Bytes article by Joe Boggs, Ohio State University entomologist.  

Another common but inconsequential pest of oak trees are the oak sawflies.  .The sawflies are slug-like wasp larvae that feed on the underside of oak tree leaves, leaving the opposite epidermis and veins untouched.  The result is “skeletonization” as shown in the image below.  Click here to see a photo of what the sawfly larvae look like as they are feeding. 

There may be 2 or 3 generations of oak sawflies per year.  Oak sawflies are a minor inconvenience to healthy trees and treatment is not usually warranted.  Treatment must be at the time the larvae are feeding to be effective.  Read more in our online article

A small, round, green oak apple gall


An oak apple gall cut open to reveal the fibrous matrix inside


Skeltonization damage to red oak leaf caused by oak sawfly larvae


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