Cactus vs Fungus

Here are the fungus found normally in cactus.

1. Cactus Anthracnose (fungus – Colletotrichum (Gleosproium) spp): This disease affects several kinds of cacti, cereus, echinocactus, mammillaria, and particularly, opuntia (prickly pear). Infection results in a rather moist light brown rot that shows many light pink pustules on the surface. Spots are small at first, later enlarge, and become covered by the small spore-producing pustules. 
Large areas may be affected, sometimes destroying entire plants. No satisfactory control is available, other than removing and destroying diseased cladodes as soon as noticed. In the greenhouse, soil from infected plants should be removed and benches disinfected. Spraying with a copper fungicide may help in checking this disease.

2. Scorch or Sunscald (fungus – Henersonia opuntiae): This disease is common and

serious on prickly pear cactus (opuntia). Spots at first are distinctly zoned, later enlarging until entire cladodes turn a reddish-brown and finally die. The center of the disease area is grayish-brown and cracked. Other fungi may be present in the diseased area. No practical control has been developed.

3. Cotton Root Rot (fungus – Phymatotrichum omnivorum): Several members of the

cactus family are susceptible to attack by the cotton root rot fungus. Infected plants die.  When pulled from the soil the brown strands of the fungus can be found growing on the root surface. No control practice is available.

4. Scab (physiological): Particularly common on prickly pear cactus. Rusty colored, corky areas appear on the stems. Scab is thought to be a form of edema, resulting from over watering and poor ventilation. Increase light and decrease humidity for control.

What to do when cactus are infected?

•        Quarantine and remove infected plant material.  
•        Repot and cut off the infected area if it’s not severe and it’s possible to cut.  Cut behind the infection so that you can throw the fungus away entirely.  If it’s severe, destroy affected plants and their pots.
•         Set the environment of your greenhouse or garden to be more appropriate for the cactus.  The causes of fungus are sometimes poor ventilation, light or humidity.
•          Dust the both infected and healthy plant with Bordeaux mixture or another fungicide.  

Preventing the fungus 

1. Back the basic, pay attention and take care of your plants closely.  Mostly, the infection can invade your garden when you don’t have time to check or care the cactus.  (This case ever happened with me, too)

2. Get rid of the fungus/infection as soon as you find it.  The earlier to figure the fungus, the easier to control it.

3. Giving more time to spray the fungicide (every one or two weeks), repot and fertilize the plants.

Every plant is same; cactus, succulent, orchid, rose or else.  If you take care of it well, it will grow up greatly and make you proud. 


If you have any comment or question, please feel free to contact me :)

When is the time to repot the cactus???

Normally, we should repot the cactus at least once a year but if you want the cactus to grow faster, you may change its pot every 5-7 months upon the size and age of the plant.

However, somebody who is very lazy (like me) may repot when it’s really necessary.  When is it???  You can notice the good time to change the cactus pot when

Hard top soil

•  Cactus size is too big for the pot 
• Cactus is growing slowly
•  The top soil is so hard 



Root on top soil

• Cactus root’s is on the surface of the pot because there is no more food/fertilizers at bottom of pot.  (Sometimes, it’s true but I have an experience: one of my cacti grown on the surface.  At that time, I changed its pot and its root was still on the surface again.  I re-potted again and its root was still on the top of the pot.  I asked my cactus advisor and she said that’s the habit of that cactus.)

my Pachypodium

However, you should know about the dormant period of each cactus & succulent.  For example, my Pachypodium always leave its leaves and stop growing since October. It will have new leaves and grow up again at the beginning of rain season (about May).  So I repot it before May.  Dormant plants are weak and can't really defend themselves against infection.  Meanwhile, any damage done to the roots during repotting will be dangerous to the plants.

Right Season to do it

Normally, I’d recommend before or at the beginning of the rain season because it’s not too dry or too wet.  And the new pot can support the plant growth in the rainy but you should be careful about the infection and being rotten if you repot during the rain season.  So please change the pot before the rain comes.

However, that’s the general suggestion.  You should understand your plants well.  There are some species that can tolerate every thing you’ve done with them, but others could not truly tolerate any stress.  So please pay attention and time to observe your cactus.