I have a number of shrubs in my Takoma Park, MD yard that are struggling. Many (most) others are not. Attached are several pictures: #1 - Dogwood - mostly sunny location, very good soil; thriving redbud, viburnum, other shrubs nearby #2 - Witch Hazel - near #1 #3 - Witch Hazel - same plant as #2, but doing well All plants are well watered.
We looked at your photos. There are several species of plants that are affected. This looks like a possible root issue. You did not mention how old the plants are. You may be dealing with poor site conditions like a wet poorly drained area, too much mulch, if the plants are new were the plants root bound in their container before planting etc. Did you add a lot of organic matter to the planting holes, etc. You will have to check the drainage in these areas. See our publication on these types of problems https://extension.umd.edu/sites/extension.umd.edu/files/_docs/programs/hgic/HGIC_Pubs/TreesandShrubs...
We notice a downspout in one of the photos. Check to see that the downspout is not dumping water in the root zone. If so, divert it to the lawn area. Alleviate any soil compaction and hope for drier weather. Do not overwater the plants.
Here is more information on the planting process and post planting care https://extension.umd.edu/hgic/topics/planting-process
All plants are many years old. None are close to downspouts. Only 1-2” mulch, if that. All in woodland environment of native trees, shrubs, and perennials.
Overall your photos show a really nice garden. The photos of the foliage does not look like a disease or insect issue. It looks more environmental in nature but we cannot say for sure what is going on. We notice an interveinal chlorosis on the dogwood and witch hazel foliage. We would like to have more information.
Is this problem new for this year? Did you have water problems last season - The very wet weather we had last year and into this spring has been tough on a lot of plants. In soil that is too saturated, roots do not receive sufficient oxygen and then decline -- which leads to dieback since the plant has less of a root system to take up water; has there been any type of construction nearby; did you do anything to the soil; etc. You can let us know.
In some cases excess water can cause micronutrient deficiencies in some plants. We recommend that you take a soil sample from the plants that show chlorosis symptoms. Take soil samples under the dripline of the plants that are affected and mix together for one sample and send to a soil testing lab. Results will give pH and nutrient deficiencies. See below.
Here is information on nutrient deficiencies https://extension.umd.edu/hgic/topics/nutrient-deficiency
and soil testing https://extension.umd.edu/hgic/topics/soil-testing
No changes other than the soil saturation. All well established - many approaching 20 years. There was a lot of off/on standing water in parts of the yard during the wettest periods. And, of course, the soil is fairly dense clay like our overall area.
I will look into the soil test. Is there a nearby lab?
See the labs listed on the link above. There are no local labs. There are private as well as University labs and they are out of state. Also see the video on how to collect a soil sample.