Wool-sower gall
Wool-sower gall

Wool-sower gall

May 4 2017 RHR 107Some of the newly installed oaks on campus appear to have grown cotton balls with pink spots. These are actually a type of tree gall called Wool-sower gall.

This gall is produced by the harmless Cynipid gall wasp (Callirhytis seminator). photo credit: R. Robert

This gall is produced by the harmless Cynipid gall wasp (Callirhytis seminator). photo credit: R. Robert

This gall is produced by the harmless Cynipid gall wasp (Callirhytis seminator). These wasps lay their eggs on a specific plant and the eggs produce the grubs whose secretions cause the gall formation. The gall provides protection and nutrition. Their favorite host plants are oaks.

The galls do not harm the tree, so the best integrated pest management practice is to co-exist. One-to three-weeks later a wasp will emerge. It is another amazing insect-plant relationship.

Becky Robert
rrobert1@swarthmore.edu
4 Comments
  • Wendy
    Posted at 10:09h, 25 May Reply

    Have never seen these before, very interesting, Have to keep our pollinators reproducing! I am really enjoying these posts, so informative, and the plants are beautiful!

    • Becky Robert
      Posted at 08:25h, 30 May Reply

      Thank you Wendy. There are some really interesting insects out there! I am always amazed how much we still don’t know about the natural world. For instance, I could find little to no info of the adult habits of this creature.

      Happy Spring,
      Becky Robert

  • Rose Martin
    Posted at 08:46h, 07 June Reply

    I just found a few oak trees that have the wool sower gall. What do I do with them. Do I just leave them be?

  • Lars Rasmussen
    Posted at 11:56h, 09 June Reply

    Hi Rose. I would just leave them be. Unless they are all over the trees in high numbers it should not be a problem. They may have hatched out by now.
    -Lars Rasmussen
    Plant Health Coordinator
    Scott Arboretum

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