|I don't use poisons to "fix problems". This
information is not reflective of my farm, it is only because
people ask about this topic in email.
Perform a checklist of sorts—
• Is the plant stressed from bad plant care? [light?, heat?,
• Is it getting way too much fertilizer?
• What is the PH of the water? Is it alkaline (bad)? Is it
heavily chlorinated (bad)?
• Is the soil healthy enough that earth worms can live in
• Have you visited a local cactus store to learn how they
care for plants?
You have to first provide healthy conditions for your
plants. Try buying some inexpensive cactus from a garden
center to see if you can keep those growing without being
sick. Establish a baseline of cactus health; otherwise your
plants will show disease because you are making them weak.
|Links to possibly useful
|I do not recommend, reply on, or
use this product. Phyton 27 is a recommended
copper fungicide for controlling root rot in
seedlings (copper kills fungus). Do your own
Phyton 27 = Copper pentahydrate
|I do not recommend, reply on, or
use this product. Sulfur is a traditional
fungicide and is used in organic agriculture. Do
your own research.
|My theory about
Fungal infection introduced through the roots (some type of damage),
or by penetration of the skin. The skin penetration theory is
supported by noticing "black freckles" form on tip cuttings—because
the spines punctured each other. Now, when I harvest batches of
cuttings, I keep them separated with blankets, cardboard, etc. They
do not stab each other and "black freckles" do not appear.
It is very likely that insects, or even wind born debris can also
penetrate the skin; this allows the fungus to enter. Then the plant
has an immune response similar to dermatitis.
What I do not understand is why one plant out of 100 will have a
temporary bout with this (like the example below) and the nearby
plants are not affected.
underneath the skin
Symptom: See my picture at right? Notice the black spot
appears like it is weeping a brown/black liquid down the
plant—spreading the infection. Look where my thumb is—you see a thin
black streak of it. It is under the skin, yet flowing like a
Cure: Leave the plant alone if the infection is minor. The
example at right never progressed. It simply got better by
itself. It turned into a tan colored scar and the plant is fine.
Summary of my experience with this:
1) Minor form: Black freckles under the skin can be benign
and harden to a point where they can be pealed off like a scab / or
they harden into a tan colored blemish. Keep perspective
about blemishes because the plant grows into a 10 foot high shrub.
2) Severe form: I've seen the black "whatever" swelling under
the skin and have seen it spread. On a vertical log I've observed it
flowing under the skin (over several days) like a liquid would if it
were on the surface. With large, swollen pustules, I've even cut
them open and drained the liquid, then flushed out with alcohol.
They always healed and the cactus never died.
However, it is not necessary to operate on them. If your plant is
otherwise healthy (proper range of light, temperature, etc.)
3) Benign: Whatever it is--I've never seen it kill a plant.
It is like a local bruise that heals (sometimes with a scar) and is
forgotten. Healthy plants seem to display this "black scab" symptom
from an injury.
I used to screw around with the black infections and drain the
liquid by cutting them open. Like popping pimples. Then flush with
isopropyl alcohol. Made no difference--they heal up on their own
naturally. From years of seeing this I am about 90% sure it is from
being scratched by the thorns of another plant. I used to get a lot
of it with cuttings until I learned from another nursery to protect
each cutting with newspaper to prevent the spines scratching their
neighbors. Now I get almost none of that. So I'd say it is like an
allergic reaction. The cacti equivalent of being scratched and
If you leave it alone the black sometimes hardens under the skin and
I had picked them off like scabs, revealing clean flesh underneath.
Or they harden in tan color scabs. But always keep in mind that this
is a tree size species! Little blemishes on small tips is nothing to
worry about. Give it a huge pot of compost/sand and let it become a
(below) My plants rarely get this condition. It could be
from a mechanical injury or some other vector of infection.
It stops and heals over.
|A tan colored raised portion remains as a
scar. Stop watering the plant and leave it alone; assuming
it is already in a healthy place (proper air, light,
|(below) Your plant is really sick.
This is a plant that is not getting good soil, the right
amount light, etc., etc. The tall spindly habit and the fact
that it is being held up with a twist tie on a pole proves
that poor plant care is responsible for this.