A possibility is Scorch. I copied the below from the attached link. Great source of pests and diseases that affect iris.

Scorch
The cause of scorch in irises is not known, although many horticulturists have studied the problem. Scorch is a pathological condition of bearded irises, but no one knows whether similar conditions in beardless irises are caused by the same pathogen. Scorch is one of the diseases that affects Louisiana irises. Aril and arilbred irises seem to be most susceptible to scorch.
Scorch does not appear to be particularly contagious since it will occur only in scattered spots of large plantings. Scorch begins with withering of the central leaves and within a few days the leaves turn a characteristic rusty red-brown, beginning at the tip and spreading down toward the base. Soon all the leaves are affected. At the same time, the roots rot and die, but the rhizome remains firm for a while after the first signs are noticed. The roots become mushy inside, then dry and hollow. Diagnose the plant at this stage by pulling it out of the ground to inspect the rhizome and roots.
To avoid iris scorch dig up the affected plants and place them in a sunny spot on asphalt paving for a week or two and then replant.
Other iris growers have had good luck if they catch the scorch early and dig the affected plants up, then dry them for about a month until they are ready to grow new roots. If you do this, it may take them two full seasons to bloom once again. In many cases, it will make better sense to discard the diseased plants. Treating the soil with calcium nitrate has helped reduce the occurrence of a similar disease in tulips and gladioli.

Here is a link that might be useful: http://www.herbs2000.com/flowers/i_pests_dis.htm

Thanks for the link. Though it is a possibility, I'd be surprised if it's scorch. It just doesn't seem to match up well with much of anything else, though.

Is it at all common for people to have these sorts of problems with rebloomers when they start sending up scapes right before the frost. I'm wondering if that's giving moisture an entry or something like that....I just don't know.

Thanks again.