Answer: Amaryllis can be affected by a fairly serious fungal infection called by various descriptive names including "red spot." However, any damage to the tissue can also turn red without being infected so a red mark is not necessarily a sign of the fungus. The disease eventually progresses enough to cause deformed foliage and stems. To some extent it can be controlled by keeping the plant in a spot with full sun, good air circulation, low humidity, and avoiding wetting the top of the bulb, foliage or stem. Sadly, it is not really treatable so a badly affected bulb should be destroyed in the trash -- do not compost it. Here is some more information about the problem.
Please note that the control recommendations in the second publication are only intended to be applicable in the state of Nebraska and even then may be applicable only to professional applicators; I am not able to tell you what might be available, if anything, for homeowner use in your area. You would need to check locally to be sure.
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