1. Arbutus 2. Rhododendron 3. Arbutus 4. Arbutus Many Arbutus are having disease problems in this area. The term Black Spot is used for the notorious disease of roses and is not what you have. Read about diseases of madrona trees and then decide what to do about yours. Do not spray anything on this - or any other shrubs - in future without knowing exactly what is wrong with it - and what specific approach is recommended. Leaves of madrona trees on my friend's Camano Island property turned almost entirely black this winter. Some years ago there was an entire conference held on diseases of madrona. Blackening of strawberry tree and manzanita (incl. bearberry) also frequent here.

Do you have a photo of a leaf underside? A few yellow leaves overall wouldn't be a concern, but dark spots on leaf undersides sounds more like an insect pest than nutrient issue....one possibility, lace bug.

I'm in Brooklyn, and I've never had any luck with evergreen rhododendrons or laurels. After a couple of years they'd turn black and die. When I put in a couple of deciduous rhodies, they were fine. They're the "Lights" type -- one gold and fragrant, the other white hasn't flowered yet but should be fragrant too. Eve

You don't say where you are, but if they were mine, it would be winter burn. The leaves that are exposed to sun and wind rather than covered by snow or shaded by other leaves are often damaged by freeze-thaw cycles and dry winds and by the lower levels of moisture in the soil even when it isn't frozen. IME they will fall off when the new leaves open or a bit sooner, and if you look closely you can see new little buds waiting to open.