The Q&A Archives: Black Soft Tissue On Tip Of Large Senita Cactus

Question: A friend of mine has a large (6ft) senita cactus he is watching for a good friend. The cactus has developed a 2-3 inch mass of soft black tissue at the tip. It has gotten worse in the past three weeks. The black tissue is only at the tip, not at the base. What should he do? Should he cut if off? Does he need to repot? If he removes the spot does he need to cover/protect the open area?

Answer: Your description sounds like bacterial rot also called wet rot. "Desert Landscaping for Beginners" by Arizona Master Gardener Press says the following:

"Wet rot, caused by a bacteria, can affect the stem tissue of cacti. Initially there is a softening of the tissue, which may be slightly darker than the healthy tissue. Infected tissue may become black, brown, red, or orange, and continues to soften. A bleeding or oozing of a dark substance will follow. Treatment involves cutting away the affected tissue with a clean, sharp knife, down to healthy tissue (which resembles a raw potato). Rinse off the area with a 10 percent chlorine bleach solution (9 parts water to 1 part bleach). Allow the area to air dry and heal."

I would not repot at this point, as transplanting is stressful. Good luck!

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