Question
I have a 3 yr old prickly pear in phoenix with small brownish spots that look like rust. We transplanted it 2 weeks ago to a new location. It is about 4 ft x 3 ft.  Any ideas what this could be? Thanks in advance

Answer
Leah,

Without seeing it, it sounds like either "scale insect" or "must" (which is a fungus). Scale insect is normally white, but when they get wet they emit a red color (native Americans used this to make red coloring). Scale insect is very hard to get rid of, picking them off being the most effective treatment.

If it is a fungus, try a commercially available anti-fungal spray (available from Home Depot). I don't know the name, but it will be in the garden section. Hope this helps. Sincerely,

Greg