Answer: Delphiniums are plagued by a number of diseases and each has a different cause. From your brief description of the problem, I'd suspect Diaporthe Blight. On plants that are just about to flower the disease takes hold and lower leaves turn brown and die. Brown spots then form on the stems at the soil line and expand upward several inches. The last stage of the disease is development of small, black, pimple-like fungal fruiting structures along the stem. If your plants display the full symptoms of this disease, destroy infected plants and replace the soil or plant your delphiniums in a different spot in the garden. Be sure to use fresh seed rather than seed you've saved from your plants. Best wishes with your garden!
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