Diagnose: Rhododendron Root Rot

1. Scrape the bark at the base of the stem and read the color underneath
2. Stained tissue that meets creamy white tissue at a sharp line is Phytophthora, the root and crown rot most Rhododendron losses come down to. The stain travels upward from the roots, so a cut at the collar catches it even when the roots are still buried. A flat white sheet under the bark that smells of mushroom, with black bootlace strands in the soil around it, is honey fungus instead. Same dead plant, different organism, and a different answer about what you can put back in that ground. White tissue all the way through at the collar means the roots are not the problem. Look at the stem itself for bark chewed or cut through all the way round, and note whether the whole plant went at once or one branch at a time. Brown margins on leaves that are otherwise green and firm are a different problem altogether, and rhododendron leaf scorch covers that one.

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