Aloe vera is prized for its ability to treat disease, but it is not impervious to disease itself. Although aloe vera is quite hardy, sick, damaged or overly moist aloe vera plants can develop a few diseases. The best cure for most aloe vera disease is prevention. Given satisfactory growing conditions, most aloe vera plants will resist pests and disease throughout their lifetime.
Aloe rust is actually a fungus that causes round brown or black spots to develop on aloe leaves. While unsightly, these spots rarely spread but are permanent. The best treatment is to prevent subsequent infection by preventing water from settling and remaining on aloe's leaves.
Basal Stem Rot
Basal stem rot is a fatal aloe vera disease that is caused by cold, damp conditions. The base of an aloe vera plant affected with basal stem rot will turn dark red or black and then quickly begin to rot. Discard affected plants and amend the growing conditions before planting new aloe vera plants.
Bacterial Leaf Rot
Bacterial leaf rot is caused by the bacterium Erwinia chrysantemi, which causes dark green, water logged splotches on aloe vera leaves. While caused by bacterium, leaf rot is always connected to over-irrigation and high rainfall in the area. Once the tissue has begun to rot, uproot the afflicted plant and discard it.