I have a weird problem going on in a raised bed that has a lot of Echium wildpretti and Echium pininana. All of the plants in a 12-inch radius of one spot are dying. You can see in this photo how just one corner of an Echium wildpretti is dying off, while the rest of the plant appears okay. I lost two Echium pininana completely within this 12-inch area. If I didn't know better, I would say someone dropped some glyphosate into a small area. Maybe a squirrel transplanted it from another garden, who knows.

Does anyone have a guess on possible causes for this selective die-off?