Ask your nurseryman to recommend a product and read the label carefully before applying. Or think of the armadillo as a beneficial creature that will get rid of the grubs for you. Armadillos also eat other unwanted insects. You might try sprinkling the soil with hot chili pepper or bits shaved from a bar of soap. You might spray a bad-tasting but nontoxic repellent found at garden centers.
Barriers can work, especially when submerged several inches.
Remove brush and tall grass, which harbor the creatures. And don't leave pet food out at night since this might attract armadillos. Most, however, use this long-flowering plant as an ornamental. According to some herb books, the Zulus of South Africa plant society garlic around their homes to repel snakes. Mail garden questions to Kathy Huber, garden editor, Houston Chronicle, P.O. Box 4260, Houston, TX 77210.