Red spider mites?

Trouble shoot problems you are having with your cactus.
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Mertzi
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Joined: Mon May 25, 2015 8:55 am
Location: Stockholm, Sweden

Red spider mites?

Post by Mertzi »

I have been spotting very small red dots on some of my cacti and wonder if this could be red spider mites? I did see one of them moving over my l williamsi, so Im certain they're insects and not just terracotta dust which they else could have been, looking at the color. I haven't however seen any webs or typical damage (dry brown scarring between the ridges) caused by spider mites. One cactus is showing a bit of brown dry spots but no webs, otherwise I belive they're all clear (yet).
My question is if there is any other common and non harmful red and very small insectes/mites? Should I wait with worrying and look for damage and webs or make an effort to wipe them out now? I prefer not to use insecticides other than rubbing alcohol and have been looking at predatory mites. Does anyone of you have experience of useing predatory mites in a house or apartment (not greenhouse), Im afraid it might be too dry for them to work effectivly...
jmoney
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Re: Red spider mites?

Post by jmoney »

Yes that is probably red spider mites.
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Mertzi
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Re: Red spider mites?

Post by Mertzi »

:( Do you think it will be enough to drip some isopropanol and keep them in the shade while it dries for the coming couple of days? Any tips for treatment? Preferably without strong toxins (strong to humans)...
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greenknight
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Re: Red spider mites?

Post by greenknight »

Red spider mites don't really look very red, they're very tiny, and don't move around much - the ones you see might well be predatory mites. That could still mean you have a mite infestation. Examine the plants closely with a magnifier.
Spence :mrgreen:
iann
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Re: Red spider mites?

Post by iann »

greenknight wrote:Red spider mites don't really look very red, they're very tiny, and don't move around much - the ones you see might well be predatory mites. That could still mean you have a mite infestation. Examine the plants closely with a magnifier.
Agreed. Any red dots, especially bright red, you spot without optical assistance are not pests.
--ian
Mertzi
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Re: Red spider mites?

Post by Mertzi »

I take it that is with normal eyesight without any 'visual impairments'? Anyway, that's very good to hear and thank you for your answers! I'll quit my isopropanol treatment for a while and keep them under watch for a while to see how they're doing. What color are "red spider mites" if not red? I read both green, red, black when I search... don't know what to look for anymore, the name seems to be slightly deceiving :P
iann
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Re: Red spider mites?

Post by iann »

Mertzi wrote:I take it that is with normal eyesight without any 'visual impairments'? Anyway, that's very good to hear and thank you for your answers! I'll quit my isopropanol treatment for a while and keep them under watch for a while to see how they're doing. What color are "red spider mites" if not red? I read both green, red, black when I search... don't know what to look for anymore, the name seems to be slightly deceiving :P
Be very cautious about anything you read on the internet concerning this pest. Much of it is simply copied blindly from other internet sources and much of that is rubbish. "Red spider mite" is simply three words and could mean anything. It usually refers to Tetranychus urticae but people use it for all sorts of mites, often not even spider mites. T. urticae is also commonly referred to as two-spotted spider mite or glasshouse spider mite. The latin name is slightly controversial and may refer to several different species.

Appearance in summer is a dull translucent straw colour. Adults show a prominent spot on either side of their bodies, actually internal structures seen through the translucent skin. Females often overwinter in hibernation and will turn a dull orange shade in this non-feeding state, but you won't often see them. Full-grown they are about 1mm long (most sources say about half a mm, but they can easily reach 1mm), easily visible to most eyes. They quickly form dense colonies and spin webs, actually just lots of individual strands of silk randomly strung around the plant. They tend to populate new growth on plants, partly for better feeding and partly because they do not grow as quickly in humid conditions, although like all mites they don't do well in very dry conditions either.

Look around on the internet and you'll find plenty of pictures of straw-coloured mites with two spots, which is the appearance you'll likely find in summer. You may also find pictures of some not-exactly-scarlet but certainly quite red spider mites. Some of these will be overwintering females, but generally they are a different species altogether, often Tetranychus cinnabarinus. You can see both on this pages:
http://entnemdept.ufl.edu/creatures/orn ... d_mite.htm" onclick="window.open(this.href);return false;
http://dimetris.com.ua/wiki/%D0%BA%D1%8 ... nnabarinus" onclick="window.open(this.href);return false;

For what its worth I have *never* had two-spotted spider mites infesting any of my globular cacti. Occasionally I've had them on columnars and opuntioids including Tephrocactus, and they are a menace on certain mesembs. I've *never* seen T. cinnabarinus (red feeding adults) on succulents anywhere, but perhaps they do occur. There are a number of other pest spider mites, some reddish and some not, but I'm not aware of them being a common cactus problem. A major problem on cacti is the false spider mite, a tiny orange-ish mite that doesn't spin webs, doesn't form huge colonies (well maybe, but your plants will be long dead by then), and likes to feed around the base of globular cacti. I have *never* seen these on mesembs so mites seem to be quite specific feeders. Orchid growers are very familiar with false spider mites (they call them flat mites), but most cactus growers are blissfully unaware of them and I've lost track of the number of plants I've seen damaged or killed without the owners ever realising they have them.
--ian
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