Severe damage to some aloes is caused by aloe mite, also known aloe wart mite or aloe gall mite, a Eriophyid mite known as Aceria aloinis Keifer (syn Eriophyes aloinis Keifer). Eriophyid mites are very small mites that are only visible using a microscope. They are worm like with only two pairs of legs and are poor crawlers with their primary method of population spread being by wind or by being moved by other creatures, such as when people transport infected plants or cuttings, or when pollinators such as birds or bees transport them between plants. Identification of a Aloe mite infestation is nearly impossible until a plant's responding gall growth begins. These galls are caused by the mite injecting a chemical into plant tissues during feeding that causes the plant tissues to grow abnormally. The resulting galls are a blister of spindle like fleshy projections found mainly on the topside of leaves, but also occurring on the flower stems and buds. These galls severely disfigure aloe plants and for this reason the name Aloe Cancer is sometimes also used to describe these galls.
Aloe mites have long been a problem in California and we have been dealing with them at our nursery since the 1980s. Though thought to originate in South Africa, where they are also pests on aloe and related plants, this mite was first identified and named Eriophyes aloinis in 1941 by American entomologist Hartford Keifer in a California Department of Agriculture Bulletin titled "Eriophyid studies XI". Keifer later reclassified it as Aceria aloiiiis in his 1952 article "The Eriophyid Mites of California" in the Bulletin of the California Insect Survey, where he also noted that it had been found on aloe plants in Los Angeles County (in North Hollywood) and San Diego County (in Pacific Beach) in 1940 and in Santa Barbara in 1941.
The first mention we know of in a horticultural journal about the damage this pest causes to aloes was in a 1984 article by Charlie Glass and Bob Foster titled "The ABCs of Cacti and Succulents" in the July-August 1984 Cactus and Succulent Society of America Journal (Vol. 56 No. 4) where the authors noted that an "occasional problem with aloes is aloe-mite. Unfortunately, too many aloe growers diagnose this problem as an interesting malformation related to crests, whereas actually it is the external manifestation of a serious disease. We have had reasonable success treating infected plants with a systemic pesticide, but as these can be dangerous to use, we would recommend that one contact a local, licensed pesticide specialist."
While some pesticide treatments can be quite effective on Eriophyid mites, the damage caused by gall is irreversible. The best course of action is to remove and dispose of the entire gall infested plant, or at least the parts so affected so not to spread the mite to other aloe plants in one's garden. We have been actively controlling this pest at our nursery for the past 20 years through our Integrated Pest Management (IPM) practices that include active pest scouting, removal of any mite infected plants and by using preventative pesticide treatments on all aloes. We are not licensed to advise about pesticide control measures but Curative and Preventive Control of Aceria aloinis (Acari: Eriophyidae) in Southern California", an article by published in the December 2014 issue of the Journal of Economic Entomology (Vol. 107 No. 6), has some good tips on control of this pest.
This page first published to the San Marcos Growers' website in March 2005 and last edited in August 2022.
Another Aloe Mite image