Oak Tree Issues: Oak leaf vein gall

Categories: Disease and Insects Trees and shrubs

I’ve already gotten several calls this spring with concerns about oak tree leaves showing damage.  In all cases so far, the oak leaf vein gall is the cause of the problem.  It looks bad and exactly the kind of thing we tend to want to reach for a bottle and “spray something” for.  Avoid the temptation, it won’t help.  The damage has already occurred.   The tree is probably going to look rough most of this season.  The good news is this is typically not a long-term health issue for the tree.  Here’s a closer look thanks to a client who sent these nice pictures into the office:

It’s easy to see how it comes by the name vein gall

Advanced stages of attack. It’s a bit unusual to see this. It could easily be mistaken for herbicide damage.

Galls (there are hundreds and hundreds of different kinds) are usually caused by tiny insects laying eggs on the leaves and then “stinging” the plant so the galls will form.  The gall (malformation) then serves to protect the next generation of the developing insect.  Back to the question of “why won’t it help to spray?”.  Once the gall forms, the damage has already occurred and insecticides cannot get inside the damaged area to kill the next generation.

Theoretically, you could kill these insects when they are laying eggs.  Three problems with that: 1.  We never know when they are going to attack, each season is different.  2.  They are nearly microscopic in size and therefore almost impossible to detect.  3.  A general spray is likely to kill as many beneficial insects as it is gall forming ones, leading to additional insect attacks later in the season.  Related to that, many people don’t realize the value some trees have in supplying pollen and nectar for honey bees.

Here is an excellent resource on galls if you would like to know more:  http://pods.dasnr.okstate.edu/docushare/dsweb/Get/Document-2304/EPP-7168web2013.pdf