Q: We moved into this home a couple of years ago in Benson. We have a lot of prickly pear cactus in the yard.Β I just noticed that some of the bigger plants have black spots on them. Is there something we can do to stop or protect the others in our yard from getting whatever it is?
A: The disease you are seeing is called Phyllosticta pad spot. These lesions are commonly seen on pads of prickly pear cacti (Opuntia species) and may be caused by several different pests or environmental conditions. However, the most common pad spot on the Engelmannβs prickly pear in the Arizona desert is caused by a species of the fungus Phyllosticta. The disease is found throughout the desert. Lesions are almost completely black because of the presence of small black reproductive structures called pycnidia produced on the surface of infected plant tissue. Spores produced within these reproductive structures are easily disseminated by windblown rain or dripping water and infect new sites on nearby pads. Pads on the lower part of plants are often most heavily infected since the humidity is higher and moisture often persists after rain. Once pads dry, the fungus becomes inactive. The lesions may fall out, leaving holes in the pads. Severely infected pads or entire plants should be removed from landscapes to prevent fungus spread.
