Knowledgebase
Dots from oak tree? #858082
Asked January 29, 2024, 7:34 PM EST
Hi. I park a car near an oak tree and I am wondering if the 1-3mm dots stuck all over my car are from the oak and what exactly they are. Photos of the dots and tree attached. I live in Northern California. Thanks!
Marin County California
Expert Response
What you are seeing might be the grass from Spongy Moth, formerly known as Gypsy Moth, larvae. Here's information from Michigan State University Extension, "Spongy Moth" to help you determine if that is the culprit.
Here's what the Audubon Community Nature Center has to say in their information, "Gypsy Moth Problems".
Finally, if you decide that indeed this is a spongy moth problem, I think the "California Department of Food and Agriculture" considers this a reportable pest. The CDFA link is to the page about spongy moths as well as the "report a pest" button.
Thanks for the reply! I can see why you might think it's moth frass, but I don't think it is. When these dots fall on a flat hard surface - like the hood of my car - they dry in a dome-shape - flat on the bottom and domed on top, which makes me think think that whatever it is must be in a liquid state when it falls through the air before it lands on my car. These dots don't appear in the dry months here in N. California so I'm inclined to believe that it could be the black "dirt" that oak trees are famous for, mixed in with either dew or rain which then becomes airborne in the wind and land on stuff. It's weird because all the dots are almost perfectly round and 1 to 3 mm in diameter - with very little variation. They also stick to car paint pretty tenaciously - another reason I think they are liquid before they dry. Could it be simply oak dirt getting blown off the trees when they get wet?
What I can find is a sooty mold, insect frass, or dripping from oak galls.
This link to "Drippy Acorn Disease" from University of California IPM discusses dripping sap from oak galls.
This link is also from University of California IPM, "Sooty Mold Management Guidelines", which details information about this common situation.
The final option of insect frass was talked about in my earlier email.
It doesn't make sense to me that rain or dew would wash something from the tree and leave the nice concentric spots, but I can easily be w wrong on that account.
There are limitations to answering plant questions on-line. For a definitive answer, if none of these options make sense, take samples of the spots into your local county extension office so somebody can examine a physical specimen and give you a clear answer.
Drippy Acorn Disease sounds promising, LOL! I'll look into that possibility further. Thanks for your help!
You're welcome. Yes, some of the names are very descriptive!
