Some Mammillarias going spineless at the growing point

[David48]

Four of my Mammillarias started to grow in a spineless, like "inermis", manner, after flowering this summer. In two plants there are signs that the spine formation is returning. Does anyone know what has caused this, and the response to treat it? I have had a few other plants get red spider mite, one thought is maybe RSM caused the problem, but only in earliest stages, the plants not seriously succumbing (I have since sprayed the collection against mite. Another thought is that the plants have been exposed to direct sun, possibly UV damage occured, but strange if only these plants were affected. Another thought is that they had all flowered prolifically, could the plants have become short of nutrients? I attach some photos. The affected plants Mammillaria densispina. mmillaria giselae, Mammillaria longiflora ssp stampferi and Mammillaria glassii ssp ascensionis.

17-06-25 Mammillaria longiflora ssp stampferi sick.JPG (161.46 KiB) Viewed 816 times

17-06-25 Mammillaria glassii ssp ascenscionis sick.JPG (173.56 KiB) Viewed 816 times

17-06-25 Mammillaria giselae sick.JPG (139.04 KiB) Viewed 816 times

[David48]

I suspect that the problem most likely has been caused by red spider mite, or a different mite. I have sprayed with a Bug Clear Ultra which advertises control of red spider, and purchased a specific miticide in preparation in case of a return of the problem. Some of the tubercles have started to produce spines later in their development.

[Steve Johnson]

I suspect that the problem most likely has been caused by red spider mite, or a different mite. I have sprayed with a Bug Clear Ultra which advertises control of red spider, and purchased a specific miticide in preparation in case of a return of the problem. Some of the tubercles have started to produce spines later in their development.

Sorry that nobody else has responded to your first post yet, so I'll chime in here...

The coastal microclimate in my part of Los Angeles is too humid for red spider mites, but flat mites certainly have been a problem. I know what their damage looks like, and I don't see any signs of it on your cacti. Red spider mites are much more aggressive, and they've been known to literally eat plants alive in a matter of days -- you don't have red spider mites either. Lack of normal spine formation is usually caused by two things. One will be inadequate light, but that goes along with other signs of etoliation -- skin has an unhealthy-looking pale color and new growth is stretched out. Again, I don't see this on your cacti. The other cause could be root mealybugs, a very pernicious pest because they'll slowly sap the life out of cacti as they suck on the juices of the root system. I'd highly recommend that you unpot one of your potentially affected plants and see if the roots are infested with mealies. If the roots look healthy, I don't know what could be inhibiting normal spine formation. However, if you do have a root mealy infestation in progress, be aware of the fact that it'll spread from pot to pot. If you decide to do a root inspection, let me know what you find.

[Robb]

This often happens to my Mamms. I find that spines just grow in eventually. I don't know why they do this, although it often happens if I fertilize frequently, so it may be because the plants grow faster than the spines can fill in? If your plants don't end up getting any, then definitely look for the pests Steve mentioned.