Here is something to be looking for in your summer strolls. The unknown leaf spot above has been found on chinkapin oaks in the southern half of Missouri since the summer of 2018. "Striking in appearance, the leaf spot has several concentric rings spreading outward from the center. This is referred to as a zonate or target leaf spot and resembles a bull's eye."
Cristulariella fungi species have been proposed as a cause and MDC Forest Health Program is working on identifying a pathogen. If you encounter it , photograph it and report it to forest.health@mdc.me.gov. The reward will be a warm feeling you have both from finding it and having a great picture. See page 6 in this PDF.
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I have recently been delving into leaf miners, the incredible story of the tiny insect larvae that live in tunnels between the upper and lower surface of a leaf before emerging from pupae as adults. More on that soon.