First, yes, you spelled it right (the generally accepted way)! I have a hard time accepting the cold-kill argument (especially for the one with no foliage on the larger trunks). It's possible, but hard to accept since you are in such a warm area (zone 8b/9a). We only rarely have significant cold-related dieback (more than a few inches from the growing tips) on crape myrtles here in Tennessee, where it gets much colder. Have you noticed any other symptoms before the total dieback (signs of disease, pests, etc)? Has anything changed (unusual weather, chemical applications, etc)? Have you contacted your local agriculture extension office and asked them for ideas? They may actually be one of your best sources of information, since they should be familiar with your local conditions and be able to take a first-hand look.

Just to help everyone understand this better: Black sooty mold is a by-product of several different kinds of insects. Aphids of ALL kinds, some scale insects, whitefly, even some leafhoppers, planthoppers, and mealybugs. All of the these insects suck large quantities of plant juices and also excrete large amounts! This is what is called honey-dew; it's a clear, sticky, sweet liquid that literally rains on anything that may be sitting underneath the infested plant. Outside, a simple mold feeds on this sweet stuff....this is the black sooty mold. BSM, thus, can grow on lawn furniture, car tops, and even on plants that are not infested with insects. Proper identification of the insect pest is important in successful control of the infestation. The BSM will eventually go away once its food source (honey-dew) is eliminated. By the way, aphids overwinter on Crapemyrtles as eggs. You can do a great deal to prevent another serious outbreak by applying dormant oil sprays two or three times over the winter and early spring.

Sooty mold grows particularly well on plants that produce a sugary exudate, if they are infested by honeydew secreting insects such as aphids, scales and the whitefly, or when infested by insects that suck sap from the host plant. Orthene is the answer.

What about something like Orange Rocket Barberry Bushes? They get max 4' tall x 1½' wide, and are somewhat cylindrical. They are very colorful with coral/orange leaves with lime edges. Many Texans are posting gorgeous photos of theirs on my other garden forum (but they are deciduous, so they lose their leaves after spectacular burgundy color in the Fall, leafing out with lime green leaves in Spring). They seem to do well in Texas. I just ordered some thru Walmart and I'm here to say that they that were some of the best-packed, healthiest plant specimens I have ever ordered from ANYPLACE on-line. Been in the ground 2 weeks and loving the sandy soil at our cabin property in Gause. https://www.walmart.com/ip/Orange-Rocket-Barberry-Live-Deciduous-Shrub-with-Colorful-Foliage/49094501?wmlspartner=wmtlabs&adid=22222222222036989139&wmlspartner=wmtlabs&wl0=e&wl1=o&wl2=c&wl3=10355304266&wl4=pla-1103074146087&wl12=49094501_0amp;wl14=%27Orange%20Rocket%27%20Barberry%20bush%20for%20sale&veh=sem&msclkid=797e9b46446919e2e048c6e69e51fca1. Perhaps these planted alternately with something that isn't deciduous so there would be color and foliage in your median in winter as well. Winter Daphne (nice blooms, evergreen throughout winter) and a lovely scent as well. They're pretty compact, too. https://www.waysidegardens.com/variegated-daphne/p/v1829/?msclkid=bffb8e9c489613230442d33c94b67df0&utm_source=bing&utm_medium=cpc&utm_campaign=Google%20Shopping1&utm_term=4582420873088447&utm_content=Vines%20%26%20Climbers