Is it just a fact of life that when yellow and white and most other colors of chrysanthemums turn "brown" a few days after it rains? I can't seem to find any logic to explain it otherwise. Is this some kind of mold that attacks the petals, or what? Maybe it's poor drainage, although I don't think that that is the problem. Thanks.

I am having the same problem with my mums. Have you had any luck getting an answer to the problem?

What you could be seeing is flower blight. All the rainfall we've had lately can create favorable conditions for fungal disease such as flower blight. Chrysanthemums are a species that is commonly affected by this disease. The white and yellow flowered varieties aren't necessarily more suseptible to the disease, but it just happens to be much more obvious because of the light flower color. Flower blight is brought on by overhead watering/rain on the flowers or high humidity.

This disease often precedes and leads to stem rot. The fungus becomes established in the flower petals and under ideal conditions moves from the flower to the pedicel or peduncle, and eventually to the stem. Symptoms appear as tannish, irregular spots on the flower petals. Flowers can also become infected in the bud stage. The buds turn brown and appear to be water-soaked. Infected buds fail to open and may sometimes abort.

chrysanthemums only bloom for a few weeks, so it is also possible that the flowers are simply expiring in their natural timeline. Most white flowers do tend to be more noticeably brown when they expire.

Should the mums be dug up and discarded or is there something that will treat them? Is there a danger of the blight spreading to other plants?

Thanks.