Answer: Based on your description I suspect your plants may be affected by the fungal disease Anthracnose, however it is very difficult to make this type of diagnosis long distance. I would strongly suggest you consult with your local county extension to obtain a more specific diagnosis and based on knowing that, determine how to proceed. If the problem is something that would require or respond to a chemical control, they will have the most up to date information on what to use and how/when best to apply it. They may appreciate photos of the overall plant and closeups of the affected foliage to show the discoloration as it begins and progresses, as well as possibly some freshly taken samples kept cool and enclosed in a clear plastic bag.
In the meantime, water only as needed to keep the soil evenly moist like a wrung out sponge (dig into the soil with your finger, if it is still damp do not water yet), avoid wetting the foliage, do not handle the plants when they are wet, clean up any browned or blackened foliage and blooms and put them in the trash to reduce sources of possible reinfection, and do not fertilize them as this can exacerbate the problem.
I am sorry you did not receive a satisfactory response from your nursery. Please understand these are independent retailers that carry Monrovia (and other) products. Perhaps a word with the manager would help, but I can't speak on their behalf.
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