Aloe mites - also known as Aloe wart mite or Aloe gall mite (Aceria aloinis) can cause severe damage to some Aloes. Related to spiders these mites are very small and are only visible using a microscope. Worm-like in appearance they only have two pairs of legs making them poor crawlers therefore it is believed their primary method of transportation is by the wind. Identification of an Aloe mite infestation is nearly impossible until a plant's responding gall growth begins. These galls are caused by the mite injecting a chemical (a growth hormone regulator) into plant tissues during feeding causing the plant tissues to grow abnormally around the mites like a protective cocoon. The resulting galls are a blister of spindle like fleshy projections - 'masses' - found mainly on the topside of leaves but also occurring on the flower stems and buds. On Aloes these galls severely disfigure the plants and for this reason the name Aloe Cancer is sometimes used.
The damage caused by a gall is irreversible therefore the best method is to remove the galls by cutting them off the plant if possible as chemical treatments applied to the outside of the gall most likely will not penetrate inside the 'mass' to kill the mites. Remove and dispose gall infested part of the plant in a trash bag so as not to spread the mites to other Aloe plants in your garden. Some chemical treatments - pesticides designed to kill spiders because they are related to mites - have little to no effect on the mites after they have been encased inside the gall. For some great info and pictures about Aloe mites visit the Dave's Garden website link below.
Sources:
http://davesgarden.com/guides/articles/view/2145/
http://www.smgrowers.
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