There are two things going on here. The eaten leaves are most likely showing damage from Rhododendron root weevils. Although the adult eats the leaves, additional damage happens when the larvae eat the roots. There are nematodes you can buy to apply to the soil that will kill the larvae. Some people put crinkled burlap under their plants and after a few days pick it up during the day and shake it out on a driveway, stomping on the weevils that fall out. The adults hide in the burlap during the day after feeding on the Rhody leaves at night. As the website/pdf given in the comment section, there isn’t an insecticide that’s labeled for these pests, but there are other physical controls and using the nematodes will help.
The spots are leaf-spot fungus. This is damage that happened last spring or summer, but is most noticeable after winter ends. Avoid watering broadleaf evergreens from overhead during the growing season and always water in the morning, never at night. If an automatic sprinkler set for the lawn is hitting shrubs, be sure that it’s only going off once a week. You could try an organic fungicide such as sulfur starting now, used according to directions, but that’s never 100% effective for leaf spot fungi and you have a minor amount on these plants.
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