Answer: After first deciding the snapdragons have black aphids, it strikes me that what you are seeing on your plants may be fungal spots. Second year snapdragon plants often develop a rust disease and it shows up as either black or rusty colored spots (pustules) on the leaves. If the black spots are not aphids (squish a few to be sure), then the plants have developed a disease. Once completely involved in this disease, the plants cannot be saved. Pull them out of your garden before the fungal spores reach your other healthy plants.
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