Pin Oak Fungus?
We have a Pin Oak tree in our yard, and something seems to be eating the leaves. Here is a photo of some type of hard fungus that is on many of the leaves. Do you know what it is? Is there anything we an do to help the tree? Other than many leaves being eaten, the tree looks to be healthy. It was planted about 30 years ago. Thank you.
These are not a fungus but a type of oak leaf gall.
Leaf galls are abnormal tissue swellings that are harmless to the tree. There are many types.
Here is a page on galls: https://extension.umd.edu/hgic/shade-tree-galls
There is nothing you need to do.
You may have had some feeding from caterpillars earlier in the season, but that is not of consequence either. Both the tree and the caterpillars have evolved together and the defoliation is not harmful on a mature tree.
Well, that is a relief! Thank you. It has got us wondering, though - should we be fertilizing it or doing anything else to ensure it's continued good health?
The best recommendation is to keep the tree well watered during dry periods and make sure mulch is no thicker than several inches and keep away from the base of the trunk.
Established trees and shrubs usually do not benefit from fertilization. Mature trees also do not need fertilizer because as trees age and mature the growth process slows down. In the landscape, woody plants receive nutrients from lawn fertilizer if their roots are adjacent to or growing in turf areas. And nutrients are provided by decomposing organic matter such as fallen leaves, decaying mulch, and minerals in the soil. Overfertilization can make the plants susceptible to sucking insects.
A reason to fertilize is if you notice poor growth, leaf yellowing, etc. Fertilize according to a soil test. Results will give pH and nutrient deficiencies. http://extension.umd.edu/hgic/soils/soil-testing