I live in Minnesota. I have an outdoor cactus garden in which I've grown prickly pear cactus the past few years.
They have been thriving. But, suddenly in the past few days I saw that a couple of them are turning black from the ground up. I have not been watering, and it hasn't rained for several days. The blackness starts at ground level, eventually moves upward and engulfs the entire plant.
Questions:
Is this caused by too much water in the soil?
If it is caused by moisture, why would it suddenly occur when there hasn't been much rain?
If it isn't caused by water, what is the cause?
How can I rescue the affected plants?
If one plant is suffering from this, can that plant infect the others around it?
If I break off and plant a still unaffected pad off the main plant that is turning black, will I be able to salvage that pad?
Thanks for all your help!
DN
Opuntia turning black
This sounds like a soilborne organism - fungus or bacteria - is causing your symptoms. Obviously, the root system supporting those blackening pads has died. Were the plants recently transplanted or has the soil been waterlogged? You may still be able to save part of the plant(s) by salvaging the top pads. If the plants are outdoors it would be more difficult to replant in the same spot, because the pathogen is soilborne. For pot grown plants I would suggest disinfecting the pot and replacing the growing medium with a coarse mineral cactus mix. If the culprit is a fungus and the plant is in the ground maybe periodical use of a systemic fungicide after planting and a soil soak before replanting will work.
Harald
Harald
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templegatejohn
- Posts: 1198
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Hi, Harald is most likely correct. It is certainly what I would have thought. The only other thing I could think of is that the roots of the plant have had too much water for whatever reasons, Heavy rain, overwating etc. This would also cause 'black rot' and a quick operation on the pads that are not black will save a terminal case.
John
John
Last edited by templegatejohn on Tue Jun 27, 2006 2:39 pm, edited 1 time in total.
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Bill in SC
- Posts: 2544
- Joined: Thu Jun 16, 2005 5:17 am
- Location: South Carolina, USA
Thanks for all the feedback.
These plants have been in their spots for at least a couple years now. Just prior to the pads turning black it had not rained for several days. However, now that I think about it, it had rained a lot about a week or so before the dry days. So, it could be that they got a lot of water.
These cactuses are outside, not in pots. How can I determine if the problem is from a soil-borne organism or fungus, or if the problem is too much water? If I have to use a systemic fungicide, any thoughts on which ones work better, if there are any differences?
For pads that are turning black, would I likely have better luck leaving the pads as is and hope the advancing blackness stops at some point, or should I cut off the end of the pad that is still green and try sticking it in the gravel?
Thanks again.
These plants have been in their spots for at least a couple years now. Just prior to the pads turning black it had not rained for several days. However, now that I think about it, it had rained a lot about a week or so before the dry days. So, it could be that they got a lot of water.
These cactuses are outside, not in pots. How can I determine if the problem is from a soil-borne organism or fungus, or if the problem is too much water? If I have to use a systemic fungicide, any thoughts on which ones work better, if there are any differences?
For pads that are turning black, would I likely have better luck leaving the pads as is and hope the advancing blackness stops at some point, or should I cut off the end of the pad that is still green and try sticking it in the gravel?
Thanks again.
Hello dn,
as I already stated in my previous post, it looks like the root system of the pad turning black is dead. Is the blackened area soft? It is very difficult to diagnose a disease without having a look at the specimen. If the problem was caused by just too much water, the organism, be it bacterial or fungal, is most likely not a very virulent kind, but an opportunistic pathogen. In that case you should think about changing the growing conditions of the plants, e.g. raised beds, amending the soil with sand, weathered granite (rhyolite), etc. in order to improve drainage and prevent another mishap. Cutting off the pad an inch or more above the darkened area, letting it sit in the air for a week or so for scar tissue to form, and then transplanting it - possibly after dipping it in rooting hormone with a fungicide like "Rootone" - will work. If, on the other hand, you have a highly virulent vascular pathogen, things are a bit more difficult. A plant without roots will not be able to uptake a fungicide and the only option I see then would be to soak the soil at certain intervals with a fungicide or - better yet - to let the sun sterilize it by first wetting it down and then placing black plastic on the wet spot. After that, you could plant the cactus. I know it would work here, because our sun is awfully strong. However, I would first look at improving drainage, if that is what caused the plant to become water-logged and the root system to drown. If you do not do anything, the black area will most likely expand until it reaches the top of your plant, and nothing can be saved at that point. You could go ahead and dig up the sick plant(s) and take a look at the root system. Most likely the roots have rotted away. If the plant is oozing you may have a bacterium that is present in it, but a fungus can cause similar symptoms and you may not see any mycelium or fruit bodies in below-ground parts.
Harald
as I already stated in my previous post, it looks like the root system of the pad turning black is dead. Is the blackened area soft? It is very difficult to diagnose a disease without having a look at the specimen. If the problem was caused by just too much water, the organism, be it bacterial or fungal, is most likely not a very virulent kind, but an opportunistic pathogen. In that case you should think about changing the growing conditions of the plants, e.g. raised beds, amending the soil with sand, weathered granite (rhyolite), etc. in order to improve drainage and prevent another mishap. Cutting off the pad an inch or more above the darkened area, letting it sit in the air for a week or so for scar tissue to form, and then transplanting it - possibly after dipping it in rooting hormone with a fungicide like "Rootone" - will work. If, on the other hand, you have a highly virulent vascular pathogen, things are a bit more difficult. A plant without roots will not be able to uptake a fungicide and the only option I see then would be to soak the soil at certain intervals with a fungicide or - better yet - to let the sun sterilize it by first wetting it down and then placing black plastic on the wet spot. After that, you could plant the cactus. I know it would work here, because our sun is awfully strong. However, I would first look at improving drainage, if that is what caused the plant to become water-logged and the root system to drown. If you do not do anything, the black area will most likely expand until it reaches the top of your plant, and nothing can be saved at that point. You could go ahead and dig up the sick plant(s) and take a look at the root system. Most likely the roots have rotted away. If the plant is oozing you may have a bacterium that is present in it, but a fungus can cause similar symptoms and you may not see any mycelium or fruit bodies in below-ground parts.
Harald
Harald's explanation is very thorough and I can't add much to it.
After reading your last post, I would say excess moisture is most likely the cause. When you say it rained a lot before, that is an important clue. It takes some time for the damage to occur as the roots start to take up the moisture just after the rain and then it slowly works its way up into the tissues. If the "water intake pipeline" (not a scientific term
) gets full and there is still plenty of water available, it keeps pumping and the cells start to burst like over-filled balloons. Then you have all this dead organic material ready to start rotting like a basket of fruit that has been left out too long.
It is important to note that this can continue to happen even after the plant is uprooted or cuttings taken. I think you are out of the woods after a few weeks, but I've had cuttings I've taken from plants that got water-logged and they continued to have a problem for days afterwards even though I gave them no water.
Daiv
After reading your last post, I would say excess moisture is most likely the cause. When you say it rained a lot before, that is an important clue. It takes some time for the damage to occur as the roots start to take up the moisture just after the rain and then it slowly works its way up into the tissues. If the "water intake pipeline" (not a scientific term
) gets full and there is still plenty of water available, it keeps pumping and the cells start to burst like over-filled balloons. Then you have all this dead organic material ready to start rotting like a basket of fruit that has been left out too long.It is important to note that this can continue to happen even after the plant is uprooted or cuttings taken. I think you are out of the woods after a few weeks, but I've had cuttings I've taken from plants that got water-logged and they continued to have a problem for days afterwards even though I gave them no water.
Daiv
All Cacti are succulents, but not all succulents are Cacti