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Pests and diseases in cacti |
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| I think as collectors of cacti we are lucky as we have very few pests and diseases to worry about with these plants. Touch wood I have never seen a vine weevil in the green-house, even though I have seen them hanging about outside munching the semperviviums and enjoying a few bedding plants. |
So who are the main pests? |
1. Red Spider Mites
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I really think these are the worst pest of all, the damage they do so quickly is devastating, you do not even realise its happening until it is too late.
The mites, that multiply at an amazingly fast rate, attack the skin (epidermis) of the plant sucking the sap and leaving your plants with a skin that is brown and disfigured, almost as if burnt. Once this has happened there is no way to remedy the damage. These are not the little red spiders you see about an 1/8th of an inch across, that appear in the summer. These mites are near invisible to the naked eye. The first clue you will see is the fine web covering the plant.
If it is a tall growing plant, then the damage is permanent. If a low growing plant, then in a few years the damage can be grown out.
With this pest we spray regularly with "Spider Mite Control" to prevent them ever getting a hold. Also during the summer months we mist the plants every evening to keep a humid atmosphere in the green-house, as spider mites thrive in a dry atmosphere and will not like this at all and it seems to keep them at bay. Should you be unfortunate and suffer an attack to your plants treat with "Spider Mite Control" (Organic control) or "Multi Rose". (If Multirose then use the ready mixed one as I don't think the mix-it-yourself one is as effective). This product is amazing and to me is the best off-the-shelf remedy by far. The mites love soft-skinned plants: Mammillarias, lophophora, echinocereus and while attacking one of these will strangely ignore the plant right next to it. |
2. Mealy Bugs
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Mealy bugs are next on my list and although not in my opinion as bad as spider mites, they are close.
These guys are always somewhere in the green house and I am beginning to believe they might be indestructible and increasing their numbers. I am seeing them on more and more plants (none cactus). We even had them arrive in the house on a bunch of grapes from a well know supermarket.
They are easy to recognise: they look like tiny pink woodlice and their nests and eggs look like tiny pieces of cotton wool. They are not shy and will make nests all over the plants.
They are also clever. If like me you mist in the evening (I do not think they like water too much) they will simply nest and breed at the back of the plant! You see a clean plant from the front, then one day you will have reason to move the plant and the back will be covered in the little mites. They make the plant grow soft where they attack and also attack the roots leaving the plants unable to function properly.
The good news is they are easy to remove. I find once treatment has been carried out the plants are soon back to good health without any lasting damage.
I treat a bad attack by removing the plant from its pot, then take the plant outside (in a perverse way I quite enjoy this bit), I hold the plant in newspaper then blast them all away with a medium fierce jet of water from the hose pipe. I also wash all the soil from the roots, this is so satisfying. If the attack is bad you will be amazed at the amount of fluff, eggs and bugs that go down the drain (the fluff and stuff float as they all have a waxy coating). After the washing is finished leave the plant to sit for a few days then re-pot. If you want to make sure they are gone give the root and body a spray over with a systemic insecticide. If the attack is light then just spray the plant with "Multi Rose" or "Buzz Off".
I have heard of other methods like dabbing them with methylated spirits but this never gets the bugs on the roots and takes ages.
I have a large crassula (money tree) that had mealy bugs on it for years; I dabbed, jetted and stabbed them, until last year I never got rid of them. This plant if sprayed with most insecticides will drop all its leaves. For those of you that have or are suffering this problem I do have the answer...You guessed it "Multi Rose"!, for the first time since I acquired the tree it has been completely clear for 2 years. Repeating the treatment over a month and pouring a capful into the soil did the job and not one leaf fell!
I just wonder how long it will be until they become immune to this spray? |
3. Slugs and Snails
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Although not a huge problem, something you should take precautions against.
I never used to have a problem with these guys in the green-house but over the last few years they seem to be sneaking in more and more. From bitter experience, I can tell you a medium sized snail can devour a 4cm aztekium hintonii in a single course. It is hard to believe that with all the wonderful flowers and plants outside to munch they take the trouble to climb up the sides of the green-house, through the vents, over all the cactus spines, until they find a cactus that cannot defend itself, to nosh! However, they will and do....you have been warned! A handful of pellets among the pots once a year usually puts a stop to this nonsense. |
4. Leaf Cutter Bees
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Quite a new one for me, I have had more of them arriving over the last few years, maybe it is something I have put in the garden that has attracted them.
They do not do that much damage intentionally but the damage is caused by their attempts to make their homes. In my green-house they like to nest in the clumping plants and in the bottom of hanging plants. They start by excavating small round holes then as the holes progress they fly off, cut some leaf, return, and start to line the hole which is quite an art. Its actually quite entertaining watching them: if while they are away collecting you move their chosen plant pot they go straight to the area where they were building and have a look around surrounding pots, then if the pot is in the green-house they will seek it out and continue their work. I do feel a little guilty destroying their hard work, but when tunnelling they go straight through everything including soft plant bodies and roots. These damaged areas can easily turn rotten; being under the soil, the wounds are easily affected by water and damp and create the perfect conditions for mould to form followed by rot.
What to do if you discover them: The first time I found one I removed the leaves from the hole then puffed the hole full of yellow sulphur hoping this would protect any wounds and deter my visitor. I left thinking this would have done the trick, I returned after a few hours to find a bee covered in sulphur, digging like a small dog retrieving a bone! It was removing all the sulphur from the hole. I watched in amazement as he then flew off, returning 5 minutes later with a new leaf, then started to line his tunnel again! I removed the leaves again and he replaced them again! Drastic action was called for! I filled a pressure sprayer with water, sat and awaited his return. I did not have long to wait! He returned with a nice piece or rhododendron leaf, as he went towards the plant I squirted him full on. He did not like it at all and retreated, but soon came back for more, after a few more squirts he left and I did not think I would see him again.
The following morning I hurried out to see if he had returned! There he was digging away and lining his tunnel again, at this point I was very tempted to squish him. In the end I removed the plant to another green house, he hung around for a while looking for it, he then was bored and started on another plant, but this time his heart was not in it and he left and never returned.
Therefore, what can be done? If you see one making a home in your plants you could squish him and that should be that, or if they become a problem hang a fine net over the vents and stop them entering. |
5. Scale Insect
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Small limpet like bugs.
I am pleased to say I have never had this particular pest in the greenhouse, so no first hand experience with it on cacti. I have had it on orange trees in the garden and sprayed with a good all-round pesticide. The problem was quickly cleared up. I can see no reason why this should be any different with cacti. |
6. Cats
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| One to watch out for here. If, like me, you leave the green-house doors open for ventilation in the summer months, beware, as cats like nothing more than using that seed tray full of three year old ariocarpus you left on the floor, under the staging, in the shade - as a litter tray. If not that, then they also find them extremely comfortable to lay in!
If you leave the door open put up a cat barrier, I use a bit of trellis across the opening. |
7. Rot
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Very few diseases attack cacti. Most are caused by bad plant care. The most common rot being caused by over watering at the wrong time of year.
Here are a few of the reasons for rot:
Watering a newly potted plant with damage to the roots.
Repotting plants in a very wet compost.
The roots failing because the soil has turned sour (a problem if a plant is left in a peat-based compost for two long).
Rot entering a wound from a cut or insect attack.
The plants getting too cold.
Sometimes it seems for no obvious reason at all.
If you have a tall growing plant that rots at the base you can simply cut off the base removing all the rot (it will be black or orange). Leave the cut part to callus for a week, then insert in new compost not too deeply and it will soon start to grow new roots again. This method will also work on globular plants if you catch it in time.
I occasionally have plants lose their roots, this happens to me with the odd astrophytum
or ferocactus. The plant feels loose in its pot, does not seem to be growing and if you give it a small tug, it will leave the soil easily. When this happens I simply wash off the base to make sure that its only the roots that have rotted, then place the plant on top of a pot of fresh compost, stabilize it with a half inch of gravel and treat it as normal. This always seems to work fine.
With lophophora I find occasionally they will develop an orange rot at ground level and if caught in time the affected area can be cut out then dusted with sulphur powder. As long as all the rot is removed this should provide a cure.
Wounds, however caused, should be treated with yellow sulphur powder to dry and disinfect them.
When cutting the plants and removing rot always use a sterile blade. As I work I dip my blade into meths or surgical spirit.
© Divine Cactus 2006
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| If you have any experiences that you would like to share and think will be of use to others, please email them to me. If I have the space, I will add them to this section. |
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