Each year around this time, as yards come alive at an unstoppable pace, we receive calls from customers and concerned tree owners all around town with questions about trees. As arborists receiving all of those calls, we’re fortunate to see patterns that help us quickly determine if an issue is an isolated occurrence or if it’s happening on numerous trees. When we receive multiple calls that describe the same concerns, we immediately consider weather patterns and how they may play into it.
This year we had a very cool and wet start to our spring, not unlike last year. One of those patterns we’ve received numerous calls about is the brown blotches and holes that many homeowners are seeing on their oaks. One half of this relates to the spring weather, the other may simply be more noticeable because of the increased overall unsightly appearance of the leaves.
There are likely two culprits at work here, an insect and a fungal pathogen. The holes you may be seeing in your oak leaves are caused by the Oak Shothole Leafminer. This feeding activity happens as the leaves are still in the bud or as they’re unfurling. Depending on when it occurs, it can even create symmetrical patterns on the right and left sides of the leaf. If we see these strange patterns, we naturally suspect one of two things: aliens, or those darn kids down the street. Alas, it’s just an insect. And a harmless one at that. The holes, while they may look alarming, will not affect the long-term health of the tree and no treatment is needed.
The brown and diseased looking portions of the leaves, usually at the tips or edges, is Oak Anthracnose. This fungal disease is active during the cooler and wet weeks of spring. By the time we see the damage to the leaves, there isn’t anything that can be done. Fortunately, just like with the insect mentioned above, there really isn’t anything that needs to be done. Leaves that are affected significantly enough may fall off prematurely, but most will persist in the tree throughout the season. While the name of this disease sounds alarming, it’s overall effect on the health of an oak is typically a non-issue.
There’s a fabulous online article that covers both of these issues and can be found on the Buckeye Yard and Garden Online website. It goes into much greater detail if you’re itching to understand the science behind what’s at work on your oak tree. Follow the link below for more information: https://bygl.osu.edu/node/1296
The Ohio State University Extension does a fabulous job with updating and maintaining this site. It is a wonderful resource for homeowners and industry professionals alike. I encourage you to explore its wealth of information and see what else you can learn about the trees in your yard and beyond.
Walter Reins | Regional Manager, Russell Tree Experts
Walter has been an ISA Certified Arborist since 2003. He graduated from Montgomery College in Maryland with a degree in Landscape Horticulture, and has called Columbus, OH his home for nearly 20 years. Walter appreciates trees for their majesty and the critical role they play in our world.