Trouble on Hydrangea, peewee, quick fire bushes
This is one of the several leaf spot fungi, probably Cercospora. Keeping leaves dry when watering the plants, and redirecting any lawn irrigation that may hit the plants, helps prevent them. Mulch around the plants, keeping mulch pulled back a few inches from the base, to prevent soil containing the fungi from splashing onto leaves
Remove any fallen leaves from around the base of the shrub and remove any spotted leaves during the growing season. At the end of the season clip off all leaves left on the stems and clean up again around the base of the plants.
There are some fungicides available to help manage leaf spot, but for the homeowner, disease management with fungicides is often not warranted because symptoms usually occur so late in the season. However, the use of fungicides may be justified for high-value landscape plantings that develop severe cases of the disease each year. Products containing chlorothalonil, myclobutanil or thiophanate-methyl are most effective when applied preventatively, prior to or at the first sign of leaf spots. These fungicides work best to protect newly developing leaves, but they will not protect new growth that emerges after the application has been made. In order to keep plants relatively free of the disease, multiple applications ( according to the label) will be necessary during rainy weather.
Here is a reference for you-
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I forgot to add, if you would like an exact diagnosia of which fungal or bacertial issue these have, you may submit samples to MSU Plant Diagnostic lab.
They need samples that show disease progressing on a live or partly live branch with some still-green leaves. Include your pictures.
See the MSU Plant Diagnostic lab for fee schedule and instructions: