WSU Extension


Armillaria root rot 
Leaf scorch 
Sudden oak death 
California gallfly 
Jumping oak gall 
Leaf galls 
Oak leaf phylloxera 
Oak ribbed casemaker 
Oak treehoppers 
Pit scale 
Stem galls 
Western oak looper 

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Caption: Oak stem galls
Photo by: A.L. Antonelli
Oak : Stem galls
(revision date: 6/26/2015)

Stem galls are caused by the feeding of several species of oak gall wasp larvae. Typical galls are enlarged or swollen. Galls associated with oak stems are often smooth and round, but may be elongate, thorny, or rough. They can be single galls or clusters of galls. Colors vary from green to reddish to brown, depending on wasp species causing the gall and the age of the gall. Many galls are also formed on the leaves. Twigs can be weakened or killed by infestations.
Management Options

Non-Chemical Management
  • Pick out and destroy galls when noticed (when practical). Many galls mature in the fall, so gall removal and destruction prior to this may help reduce numbers of wasps in the spring.
  • Prune out unsightly galls to improve tree's appearance, when practical.
Select non-chemical management options as your first choice!

Chemical Management

None recommended.


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Caption: Oak stem galls
Photo by: A.L. Antonelli
Caption: California gallfly "oak apples"
Photo by: R.S. Byther