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False Spider Mites on Cacti
Photos by Bob Hammon, CSU Tri-River Extension Office, Grand Junction, CO

{Having found some suspicious patches of orange crust defacing some of my cactus seedlings, I took one of the plants to the CSU Tri-River Extension Office to have the problem identified. It turned out to be an orange mite, as shown in the microphotographs below by Bob Hamman, the Office's entymologist. These mites are visible to the unaided eye only as minute specks. With a 10x magnifying loupe, they are just discernable as creatures. The recommended remedy, which seems to have done the trick, was a couple sprays of all-season oil a couple of weeks apart (1 Tbsp./gallon dilution). The cacti tolerated the oil with no problem (though they were not in full sun).—Tom Burrows}

Comments by Casey Sclar, Plant Health Care Division Leader, Longwood Gardens Inc.:

Looking at the pictures alone, I'm thinking that what you have is probably a tenuipalpid (false spider) mite (Acari: Tenuipalpidae). Possibly Brevipalpus russulus (Boisduval)?

Here's an old description: http://www.freshfromflorida.com/pi/enpp/ento/entcirc/ent188.pdf

Here's what the cacti people are saying: http://cactiguide.com/forum/viewtopic.php?t=19239&sid=ae8dbb743c1caa1fcc5305b27f5bc8b3

Nice drawings and description from New Zealand: http://www.ento.org.nz/nzentomologist/free_issues/NZEnto10_1_1987/Volume%2010-131-133.pdf

There's also a short description in "Mites injurious to economic plants."


Mite damage on Pediocactus simpsonii seedling. This stem is about 1/8" in diameter.
(Click to enlarge: 1280x960)


Mites in situ on Pediocactus simpsonii seedling.
(Click to enlarge: 1280x960)


Mite, isolated.