I have an (white?) oak about 24" DBH that has lost about 70% or more of...
I have an (white?) oak about 24" DBH that has lost about 70% or more of its new leaves. This has happened in the past week or so. I thought maybe I had accidently poisoned it with some weed killer but upon closer inspection, I found that the leaves seem to have a parasite on their bases. I am enclosing a picture because I cannot find anything on this--sudden enormous leaf loss from a scale or thrip or whatever this is. The picture has two leaves. Note that they are green on the stem when they fall off. The white spot turns buff color after the leaf dries out. Can you tell me what this is and how to control it before I lose my tree? Thanks!
Hamilton County Ohio
Hi. Thanks for sending a photo. Based on that and the symptoms you describe, I think you are most likely dealing with oak anthracnose. Anthracnose is a fungal disease, and in oaks, it is caused by the pathogen Apiognomonia quercina. It affects newly-expanding leaves, particularly during cool, wet springs, which matches the conditions experienced in many parts of the state this year. The leaves in the photo you sent are pretty far gone but, as you note, the stem (petiole) itself seems to be fine; it is just the leaf tissue itself, though virtually all of it is dead (necrotic) and distorted. Although the effects can be dramatic, usually no treatment is warranted except in extreme cases. Note also that the effects often appear worse than they really are because the lower branches are usually most affected by oak anthracnose because they tend to stay cooler and wetter than other parts of the tree; it is likely that fewer leaves in the upper part of the tree are affected. Ohio State U. Buckeye Yard and Garden Online newsletter had this nice post on “scuzzy looking oaks” last year. It discusses some oak issues commonly seen in the spring, including oak anthracnose. This article on oak diseases from the U. of Illinois is also good. You will note that many other oak issues do not show up until later in the growing season, which is another clue that suggest you are dealing with oak anthracnose. It says “Disease management strategies should focus on promoting tree vigor. Large trees can be pruned to improve air circulation. Raking and disposal of infected leaves can be helpful, especially on smaller trees. Proper watering and fertilizing of the tree is recommended to help reduce tree stress and susceptibility. Fungicides are not usually warranted or recommended for ornamental trees unless the disease is a chronic problem on young trees.” Since your tree is well-established, I think you can just focus on cultural practices. This article from the U. of Massachusetts makes similar recommendations about cultural practices that can help with disease management. Unfortunately, weather has a lot to do with the prevalence of the disease, and obviously there is no way to control that! That article also mentions small “pads” (known as acervuli) that are produced by the fungus and are responsible for the production from most of the spores. I suspect that is the white spot to which you refer at the base of the leaves.