Q:Â My prickly pear appears to be turning black in places. Also, the saguaro and the tree next to it seem to have a brown substance on the base. Are these termites? If so, how do you treat or is it too late?
A:Â Your prickly pear appears to be suffering from Phyllosticta pad spot, a fungal disease commonly seen in our area. It is spread by wind and rain so it travels easily from plant to plant. You can remove infested pads and plants if you like.
There is no way to prevent it from happening so managing the plant by pruning is really the only option. The saguaro may have termites; it is hard to see from the photo. Typically desert encruster termites (Gnathamitermes perplexus) will colonize the outside of older saguaros where there are dead woody areas. They bring their mud habitat with them so you might see what looks like mud caked on the base of the cactus. Scrape a bit off and you might see the small white termites run for cover. Since termites are only after the dead wood, the live part of the cactus is safe from harm.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Email: plwarren@cals. arizona.edu
