One of the easier plants to grow indoors, cacti do have issues with brown leaf spotting from time to time. Most problems can be solved with a change in environmental conditions. Does this Spark an idea?
Air and Light Requirements
According to the North Dakota State University Extension website, brown leaf spotting may be a sign of light overexposure or dry air. To remedy, move your cactus to a room with more humidity and less direct sunlight, and mist the foliage with distilled water to rehydrate.
Scale Infestation
Scale, an insect often seen on indoor cacti, can cause brown spotting on the leaves. To get rid of the infestation, treat the infected area with a cotton swab of horticulture oil, which cuts off the insect's air supply.
Under- or Overwatering
If your indoor cactus is getting too much water or not enough, brown leaf spotting may occur. Identify the species of your cactus plant to determine how much water is needed. For example, Christmas cacti require drier soil than other varieties, and overwatering may cause leaf spotting and fungal diseases. Other cacti may need more water to survive.
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