Q: Attached is a picture of a barrel cactus in our yard that has begun to turn brown in recent weeks. This is the third one to do this in the last six to 12 months. What might be causing this and what can be done to prevent it? Is there any hope of salvaging a barrel once thisΒ begins?
A:Β It looks like an internal soft rot caused by species of Pythium, a soil borne pathogen that is favored by moist conditions. Pythium species can cause root and/or crown rot if plants are placed in the ground too deeply when transplanted or are wounded and then over-watered.
If a wound occurs before or during monsoon season, it could become infected through exposure to rain water carrying the pathogen. If you plan to replace this barrel with another, please keep in mind that barrel cacti should be planted so that the roots are placed firmly in the soil but no soil is placed around the base of the plant. Since the rot is internal, it is often too late to treat cacti once disease is detected. The best prevention is proper planting and watering.
Peter L. Warren is the urban horticulture agent for the Pima County Cooperative Extension and the University of Arizona. Questions may be emailed to
