Cotoneaster Leaf - Yellow with black spots
About 5% of the plant is covered with these leaves. Two leaves that were stuck together had some whitish residue that had a cotton-like texture, and a hole suggesting insects. I saw smaller bits of whitish stuff elsewhere. I do think the table was just dirty.
So far this year it was mainly be watered by rainfall. Since the weather has warmed up, I have started hand watering plants--just a hose with a shower style extension.
This is possibly black spot, a fungus. Cotoneaster is a genus in the rose family, which is famous for black spot. Fungal diseases commonly appear in the spring, having overwintered on the plant or plant debris on the ground. Spring rain, overhead watering, inadequate air flow with a plant help to spread the fungus. Your cotoneaster doesn’t appear to have a big problem with air flow but a light pruning to ensure that would be helpful. The affected leaves and the debris on the ground should be removed as soon as possible. Be sure to disinfect your pruners between each cut to avoid spread to a new area of the plant. Dispose of the material in your trash, not in compost. Find more information about black spot here https://pnwhandbooks.org/plantdisease/host-disease/rose-rosa-spp-hybrids-black-spot
The white cotton-like substance you described could indicate an insect pest. If that is the case I still recommend the cleanup process above.
At 5% it seems controllable if action is taken now. I do not recommend any kind of chemical control because we have not definitively identified the problem. Keep watch on the plant and continue removing damaged material. When our clinic at the extension office opens again consider bringing in some samples to be physically examined if the plant is still struggling. You are in Clackamas County so the nearest office to you is the OSU extension office at 200 Warner Milne Road
Oregon City, OR 97045. Call ahead to make sure the office is open and staffed (503-655-8631)
Thank you...I do have roses in the yard and battle with black spot, like most people I imagine. Thank you, Alex