Q. My Euonymus shrubs at the shore are dropping leaves and some have a black sooty substance and some have brownish spots. What is it and what can I do?
It sounds like you may have a case of scale on your Euonymous plants, which is not uncommon for Euonymous. The brownish spots are probably the scale which should be a raised spot and hard and can be moved by a thumb nail. The sooty substance is a fungus that grows on the excretia from the scale. If you spray the plant with ultra-fine oil, which is in most garden centers and hardware stores, the scale will eventually be killed. It might take more than one spraying, but the oil is completely non toxic to us. It works by smothering the scale with a thin layer of oil. The ultra fine oil also will kill the crawling stage of the organism if it is present. I would not spray the plant in the hot sun, but wait for the cool of the evening. The plant should recover and have new growth after the stress of the scale is removed.