by Mike Hillstrom, forest health specialist (Fitchburg). Michael.Hillstrom@wisconsin.gov;
208-513-7690

Oak leaf fold galls on red oak leaves. Photo: Mike Hillstrom

Ethan Lee, parks supervisor for the City of Janesville, recently reported symptoms of oak leaf fold galls on an oak tree on the University of Wisconsin – Rock County campus. Oak leaf fold galls, caused by fly larvae, are generally harmless to trees. However, new information links oak leaf galls with a recent invasive mite from Europe, Pyemotes herfsi, commonly called the oak leaf itch mite. Although no evidence of itch mite was found on the affected red oak tree, more than 50% of the tree’s leaves contained leaf fold galls.

The fly larva that causes oak leaf fold galls. Photo: Mike Hillstrom

When present, itch mites can cause an irritated rash and redness of the skin, sometimes accompanied by small, pimple-like bumps. If you develop symptoms after being near oak trees with oak leaf fold galls, please let your regional forest health specialist know. There are currently no management recommendations for the itch mites.

For more information, visit:

• https://bygl.osu.edu/node/786
• https://ento.psu.edu/extension/factsheets/pdf/OakLeafGallItchMite.pdf