Ask Mr. Smarty Plants

We hope that your  Mahonia trifoliolata (agarita) doesn't look like these pictures in this website by Bob Harms at the University of Texas, Barberry webworm. The adult form of these larval beasties is a grayish brown moth with about a 2" wing spread that belongs to the family Pyralidae ("snout moth"). This moth and its larva are often connected to members of the Berberidaceae or Barberry family, to which the Mahonias, including agarita, belong. The name of the caterpillar involved is Omphalocera dentosa, so at least when you are swearing at them, you can call them by name. According to this Connecticut Agricultural Experiment Station site Barberry (Berberis), control is rarely needed. In the event of an infestation, they recommend the application of Bacillus thuringiensis var. kurstaki, or spinosad, which are among the compounds registered for control of this pest, to young caterpillars. Consult the label for dosage rates and safety precautions.

The Lady Bird Johnson Wildflower Center recommends neither for nor against the use of pesticides, and you will have to be the one that decides if you need to apply controls. We would suggest you contact the Comal County Extension office and see what suggestions they have, as they are likely  to know more about the situation.

Mahonia trifoliolata