Cardinal Flower has no major disease or insect issues. Slugs may periodically eat the leaves but prefer hostas and other plants over this one. Mammals, including deer and rabbits, will generally avoid eating it as well.
Cardinal Flower is a member of the Lobelia genus, and contains an alkaloid called lobeline, which discourages animals from feeding on it. Lobeline is toxic to humans, so be mindful when siting it around children and pets.
An often-cited drawback is that it’s a short-lived perennial, lasting only 2-3 years in a typical landscape. However, proper mulching and moisture can help prolong its lifespan, and the plant can self-seed if conditions are right.