Hello Kerry,

It's difficult to tell just from leaves what is going on with your oak. It helps to see the full picture of the tree's canopy as well as its trunk and what the base of the tree looks like. Has there been any recent physical damage to the tree's trunk? Damage can open the tree to disease vectors. Sometimes the leaves alone, like the ones you show in the photos (alive with symptoms), can be tested for diseases. If you'd like to try that route, the U of MN Extension has a plant disease clinic to help with that. Here is a link to their website where you'll learn about their services, prices, and how to submit a sample.

Has there been any recent herbicide spraying nearby. It doesn't need to be on your property. Herbicide applications are discouraged (illegal if done by a professional) on windy days. In that case, the leaves may be showing stress from that incident. If you are able to recall such an event, ensuring that your tree is consistently watered for the rest of the season will do a lot to help it recover. I recommend an inch of water per week. Measure your rainfall (we've had a lot lately but sometimes it's spotty). July and early August are typically dryer so be sure to water then. And when you water, make sure the inch of water is applied out to the farthest reaches of the tree's root system. I've Included a diagram of the reach of a tree's roots -- well beyond the drip line of the canopy.

But it may be far more economical to contact a certified arborist who can evaluate the entire tree and make a suggestion as to what the issue is. She may still suggest testing. Here is a link to information about how to find and hire a professional.

Good-luck!