Trichocereus pachanoi cristata with white spot

[Virginia]

Hi everyone,

I've been growing this Trichocereus pachanoi cristata (also known as San Pedro cactus) for over a year now and it seems pretty healthy except for a white spot that has recently appeared on it, and which seems to be expanding (see image).

t's not soft and that area is not particularly exposed to the sun (in fact, its opposite side receives more direct sunlight). I was wondering if anyone has a remote idea of what could be happening.

Many thanks for your help, and please let me know if more details are needed!

[Steve Johnson]

Hi everyone,

I've been growing this Trichocereus pachanoi cristata (also known as San Pedro cactus) for over a year now and it seems pretty healthy except for a white spot that has recently appeared on it, and which seems to be expanding (see image).

t's not soft and that area is not particularly exposed to the sun (in fact, its opposite side receives more direct sunlight). I was wondering if anyone has a remote idea of what could be happening.

Many thanks for your help, and please let me know if more details are needed!

From what I can see in your photo, you appear to be growing it in a mix that's too rich for desert cacti -- mostly soil with chunks of tree bark. You should lean it out a lot with mineral gravel for better drainage and aeration of the roots. The choices are pumice, Perlite, crushed granite poultry grit, Seramis, and calcined clay cat litter (not regular cat litter!). I recommend that you do the following:

• Unpot the plant and clean the soil out of the roots as thoroughly as possible -- squeaky-clean or at least close to it.

• Soak the roots in 1% Hydrogen peroxide for 30 minutes (longer is fine). This does 2 things -- first it kills any potential plant pathogens that could induce rot. Second, it promotes faster healing of the roots when they settle in after repotting.

• Let the roots dry out completely, then repot the plant in fresh, dry mix.

The soil should be dirt with a minimal amount of organic materials such as tree bark. Picking out all the big chunks is helpful. Avoid potting soils containing
peat -- takes forever to wet and forever to dry out. Since you live in a desert tropical climate, my guess is that the right mix for you should be 60% mineral gravel and 40% soil. Be sure to mix the ingredients, don't layer them. Layering creates a perched water table which causes all kinds of problems. When you repot, let the plant settle in for 2 weeks before you water it. Allow the mix to go from wet to dry top-to-bottom between waterings.

For good or ill, everything starts out in the roots -- if you've been using the same soil for your Pilosocereus, that's probably the reason why its growth point could be either dying or dead.

[Virginia]

Hi Steve,

Thank you so much for your fast and detailed answer - much appreciated! I'll do what you recommend right away.

Ps. No, the Pilosocereus is potted with proper soil - the San Pedro is mine but looked after by my brother (in a different house I mean).

Thank you again, Virginia

[Steve Johnson]

No, the Pilosocereus is potted with proper soil...

See this:

http://www.cactiguide.com/forum/viewtop ... 50#p389668

Don't know about jungle cacti, but desert cacti with roots in the peak of health generally don't get fungal infections. If that's what you're dealing with (and I'm 99% sure that you are), I wonder if you still have too much soil in the mix. I grow my cacti in a soil-less mineral mix and I've never had fungus problems, so unfortunately I can't give you any guidance on whether or not your mix could be a breeding ground for fungal disease.

[Virginia]

Ok, you convinced me I'll repot the Pilosocereus. But maybe wait until it heals from the cut, right?

[Steve Johnson]

Ok, you convinced me I'll repot the Pilosocereus. But maybe wait until it heals from the cut, right?

Right -- there's no urgency about repotting it, so take your time and wait until the Pilosocereus' cut forms a nice, hard callus. If any dirt gets on it when you repot, you can simply blow it off. You'll be fine as long as you do the repot with dry mix as I recommended. One thing I wouldn't recommend is watering the plant before its roots settle in for 2 weeks after repotting. Best way to kill any fungus spores in your current soil is by letting it dry out "to the bone".

Pilosocereus is easy to grow, so if you treat it right in a leaner mix and don't overdo the watering, you should be on a good track for recovery and healthier growth in the near future.