Termites on cacti are fairly common and don’t need to be treated. They are only interested in the dead wood on the outside of cacti and can coexist with these plants.

Courtesy of Michael J. Plagens.

Q: We have a very large/old saguaro in our front yard, as well as some other barrel cacti and other saguaros. About two years ago, we discovered we had the beginning of termite damage in our ceiling (attic space). We had the home treated and no problems since. The termite company said they were subterranean termites and that we may see the termites move and begin to do minimal damage to other wood outside the home. I started noticing what I believe are termite tunnels on our large saguaro. The damage became more evident later as the tunnels turned into craters left on the saguaro. The saguaro seems to be surviving. Now I’m noticing what looks like evidence of termites in the barrel cacti. Should we be treating the termites attacking the cacti or will they cause minimal damage and move on to other sources? Are they also subterranean termites and could you recommend a treatment that would not harm the succulents?

A: Termites on cacti are fairly common and don’t need to be treated. Termites are only interested in the dead wood on the outside of your cacti and can coexist with these plants. They are likely desert-encrusting termites (Gnathamitermes perplexus) rather than the subterranean variety that infested your attic. Termites are categorized as decomposers and they help recycle dead plant material into soil. It’s only when they get into our homes that we should be concerned and you already took care of that part.

Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to tucsongardensage@gmail.com