Tuesday, October 6, 2015

Aloe mite sighting at Home Depot in Morgan Hill, CA

On the way home from the 2015 Succulent Extravaganza I stopped at the Home Depot store in Morgan Hill, south of San Jose. I got excited when I spotted a grouping of large succulents outside the entrance to the garden center. The boxed agaves turned out to be plain old Agave americana—seriously, who would spend money on those? Dasylirion quadrangulatum was tempting for $59.99 in #15 cans but they were no bigger than what I already have. But then there was Aloe ‘Erik the Red’. I already have one, but the flowers are so nice, I wouldn’t have minded another one. Aloe ‘Erik the Red’ was also $59.99 in #15 cans.

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A good price for large plants.

But were they healthy? Not so much.

Even feeble-eyed me spotted the problem right away:

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Take a closer look:

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Nasty-looking, isn’t it?

Gardeners in Southern California are probably familiar with this disease, but here in Northern California is isn’t wide-spread yet.

I’m talking about aloe cancer caused by mites, the scourge of aloe growers in the Southland. Aloe mites are microscopically small spider relatives—arachnids instead of insects. As the mites feed on aloes, they secrete a chemical substance that causes abnormal tissue growth, often resulting in a solid mass (called a “gall”) developing around the mites. This gall protects the mites both from predators and from topically applied chemicals. While the mites and the abnormal growth they produce (often referred to as “cancers”) rarely kill the plant, they can cause wide-spread disfigurement. And what gardener wants a plant that has the horrid-looking growth you see in the photo above?

There are no easy treatment options for this disease. Insecticides don’t work since mites are spiders, not insects. Topical miticides (mite killers) aren’t effective either because the mites hide deep within the misshapen tissue. Some growers says systemic pesticides work because they’re taken up by the roots and spread into the plant tissue so the mites die after feeding, but there’s no consensus on this.

If it’s a plant you can live without, tossing it is the safest option. Otherwise you can cut away the affected tissue with a sterilized knife. Sunbird Aloes uses a new treatment that involves cutting away the cancer, letting the wound dry and then painting it with undiluted formaldehyde (widely available online, including on Amazon).

Lucky me, I haven’t encountered aloe mite damage on my aloes yet. But if—or rather when—I do, I’ll give the formaldehyde treatment a try.

The best option, though, is prevention. Buyer beware, and all that. If you see obvious signs of mite damage, don’t buy the plant and tell the nursery why. I stopped an employee at Home Depot and told her what I’d seen but she seemed rather disinterested. I wouldn't be surprised if the same aloes are still sitting there, waiting for unsuspecting customers.

USEFUL LINKS:

There are many articles about aloe mites on the Internet, but in my opinion, these two cover all the bases:

13 comments:

  1. That is no bueno...perhaps an email to the store manager , linking to this blog post will help ? Chances are the employee you spoke with was not one of the few who work there who actually knows something about plants.Maybe a higher-up would be more concerned about being an agent to spread these mites northward. Not good for the brand !

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    1. I'll see if I can find an email address for the garden center manager of the Morgan Hill store. I was too tired to pursue it when I was there (plus I had another two hours of bad traffic to deal with).

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  2. I can just see that employee rolling her eyes as she walks away from you. Makes me angry!

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  3. Oh my! Where's their quality control checker?....

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    1. I don't know if Home Depot does quality control inspections on plants. But the grower should never have released these plants for sale. The signs of mite infection were obvious from 5 feet away!

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  4. Eeeeewww...! (Kind of related: I've seen some nasty agave mite-infected plants at the local Home Despot.) Buyer beware indeed. Aloe maven Buck Hemenway advised to treat the cut area on an aloe you wish to keep with a 10% bleach to water solution. And Buck always said that if you collect aloes, you will get aloe mite :~( Had one case here, on a little aloe from a cactus club sale. Into the trash it went.

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    1. I'm not surprised. Agave mites are just as much of a problem. Knock on wood, I haven't found any infected plants in my collection yet.

      Thanks for sharing Buck Hemenway's treatment. Much easier than getting formaldehyde!

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  5. A Home Depot garden department employee not caring? Shocked! An informative sheet about Aloe mites (including photo) laminated and stuck on a stick in one of those pots would be a guerrilla option, and I bet it goes unchallenged by anybody in an orange smock.

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    1. I love that idea! I should make up a bunch of laminated signs and have them ready. We even have a laminator somewhere...

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  6. The big box stores generally don't own the plants they sell. The stores rent space to growers, who are responsible for maintaining/restocking. The growers only make money on the actual plants sold. If you go when they are restocking you can see that none of the people taking care of the plants or restocking actually works for the store; they work for the grower.

    Systemic seems to work on gall mite; I had an infestation on my Kumara plicatilis, a plant that was quite large that I didn't want to lose. I cut off the entire fan that was infected, sprayed the cut with Sevin, then gave the plant a dose of Bayer Tree and Shrub Protect And Feed. I've cut off the flowers since then so no bees can be affected, in case the systemic is in the flowers. The plant has been clean since, about 4 years. If it is a small or common plant I just throw it out. I threw out broomii a few weeks ago, not only a bad infestation at the base but the growth point had rotted. Oh, well.

    I'm thinking its a good idea to buy any Aloe small and young and grown from seed is good. Then blast it with systemic at that size, on arrival, then by the time it's large enough to flower, several years on, the systemic should be isolated in older tissue or out of the plant by then and the flowers will be safe for bees. I have read that Hummingbirds can unfortunately spread the mite if the flowers are infected; not sure if that is true or not.

    I once spent quite a lot time looking for information on the internet; it seemed like there's very little significant research being done on gall mite because Aloe is not a food crop.

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    1. Great info, Gail. I didn't know that about the growers "renting" space at the big box stores. Hard to wrap my mind around that way of doing business, but it wouldn't be the first time I can't quite understand the practices of large corporations.

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  7. Yikes! I haven't seen - nor heard of - this. Thanks for the heads-up. Thanks to Hoover Boo as well for the advice on treatment.

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