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I live in the UK and have a Trichocereus bridgesii/Echinopsis lageniformis "monstrose" cactus that I bought from a garden centre 3 years ago. Every year in early summer several new stems grow from sections on the existing stems near to the spines, starting as a bright green colour and growing throughout the summer until they slow down and turn a darker green around September.

Unfortunately I've always found that near the end of this growing period the surface of some sections of the new growth appears to "dissolve" - looking almost as if it has been burnt off by acid - revealing bright green flesh underneath which quickly forms into a white crust. Luckily once the growing season finishes this whole process stops too. Here's a picture:

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I'm not sure whether this is a pest or a fungus or otherwise something to do with the plant itself. It spends most of the year inside and sheltered from the damp cold UK weather with minimal watering during the autumn/winter months and every 2 weeks or so in spring with regular feeding. In the summer I put it outside when it's warm and sunny, and I wonder if it could be getting infected when I do this, but I've never seen any small insects on the cactus. Also the repeated occurence of this white crust every year - as well as the fact it stops spreading when the plant stops growing in autumn - makes me suspect that pests might not be the problem. But I'd like to be able to stop it happening this year because it looks very unsightly and I'm quite fond of this cactus!

If anyone recognises this disease or has experience with this species of cactus and can give me any tips on how to prevent it returning this coming year I'd be really grateful. Thank you!

Alex Saad
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1 Answers1

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What you're seeing there is quite normal callous formation - it's a bit like a scab when you've cut yourself. The cause of the corky callous layers is damage - either from insects, or sudden chilling, physical injury and sometimes, underwatering in summer.

I'm no cacti expert, but it's possible, from your description of some of the new growth 'dissolving' towards the end of the growth period, that it's being caught by colder temperatures, particularly if its outdoors. New growth would be particularly vulnerable to changes in temperature, and that might explain why those areas die back. Once they die back, callous formation is both inevitable and healthy, although, of course, unattractive.

It may also be that you are overfeeding, causing excessive growth which will be particularly weak and susceptible to both sunburn and a drop in temperature - this particular cactus is not a fast grower. As you're in the UK, I'd be inclined to keep it indoors all the time, but somewhere with good airflow, bright daylight and a little winter sun, to avoid both the possibility of anything 'grazing' on the plant, or fluctuations in temperature damaging the plant.

Some info in the link below which might helpful - you will note it talks about this plant being pretty cold hardy, but that's only once its acclimatized, it won't like sudden changes in temperature

http://www.cactus-art.biz/schede/TRICHOCEREUS/Trichocereus_bridgesii/Trichocereus_bridgesii_mostruosa_B/Trichocereus_inemis_mostruosus_inemis_B_penis_cactus.htm

Lastly, cactus can get scale infestation - these look like raised little beigy brown discs or bumps, so you might want to check that isn't a problem by inspecting the smaller areas of damage to make sure there's not an active infestation currently.

Bamboo
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