Ask Mr. Smarty Plants

The reason we were so fast is that we answer very similar questions frequently, and just referenced one of them. We knew it was too easy. The only thing we can think of that would make off with most or all of the leaves on a plant is the leaf-cutter ant. Please read this previous answer, which was from San Antonio; Hays County is close enough to Bexar County that they could have spread there.

Ordinarily, when insects are the cause, they are things like spider mites or aphids that pierce the leaf and suck juices out of them. They make unsightly holes, and can eventually do a lot of damage to the plant, but they don't eat the whole leaf. In fact, they live on the leaves they are sucking on, and raise their children. If you see any ants, they are farming the bugs, collecting the "honeydew" exuded by the bugs. The cutter ant, however, although also a farmer, takes as big a chunk of leaf as he can carry home to the tunnels where the queen is laying eggs. They usually work at night, which might explain why you have seen no bugs. The answer we have linked you to has more information.

Since we are neither entomologists nor plant pathologists, that about empties our stock of wisdom about your problem. As we did in the linked answer, we suggest you contact the AgriLIFE Extension Office for Hays County, and see if they have had other reports of similar problems.