Water-soaked black and brown spots on plant leaves and stems often indicate a fungal or bacterial disease is the problem. Adjust the watering schedule and do not allow plants to sit in excess water.

Many of the leaves were covered with irregularly shaped brown, dead spots. As soon as we approached the trees I had a pretty good idea what was going on.

However, the most common pad spot on the Engelmann’s prickly pear in the Arizona desert is caused by a species of the fungus Phyllosticta. The disease is found throughout the desert.