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

Authors:

Links to this article are strongly encouraged, and this article may be republished without further permission if published as written and if credit is given to the author, Yard and Garden, and Iowa State University Extension and Outreach. If this article is to be used in any other manner, permission from the author is required. This article was originally published on August 30, 2019. The information contained within may not be the most current and accurate depending on when it is accessed.