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My succulents get a rubbing alcohol spray quite regularly to kill them
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Thermoman wrote:After a long and frustrating battle with red spider mite – mainly of the false variety – victory finally came into sight this summer (short as that may have been). Then the mealy bugs moved in and a new battle started against both normal and root varieties. I can sympathize with the correspondent who felt like giving-up growing cacti as a result of these pests.
A major difficulty proved to be finding something to deal with the blighters. Several contributors to this forum have complained that virtually everything that has proved effective in the past has now been withdrawn. Some cactophiles even admit to keeping secret hoards of unmentionable banned substances. Provado is still around but I must admit that, like others, I have found it to be less than effective – and expensive!
The break-through came while I was working my way though a collection of partly-used insecticides I found in my wife's greenhouse, amongst which was a bottle of Wilko's Rose & Flower Bug Killer. This proved to be the Corporal Jones solution. Red spider mite and mealy bugs most certainly 'do not like it up 'em'.
Alerted to surfactants I next tried Savona. It was effective but, as another frustrated contributor to this forum pointed out, its efficacy almost guaranteed its withdrawal from the market, which I believe has now happened, or is planned. Remaining stocks are, perhaps inevitably, now blighted with profiteering. What was available just a few months ago for £17 per litre is now fetching nearly £40 per litre but perhaps that's an advantage. It spurred me on to find an alternative.
'Potassium, or Sodium, salts of long-chain fatty acids' are more commonly known as 'soap'. So, I bought a bag of soap flakes – just ordinary soap flakes, not the much dearer horticultural variety. The made-up insecticide it produces costs about 1 or 2p per litre, depending on how much you pay for your water. That's roughly one thirtieth to one fortieth of the cost of Savona, which, incidentally, also suffers from the fact that it stains. Some of your prized white-haired or white-spined cacti may turn yellow. That seems to wear off eventually but I still have a few mammillarias that appear to have misjudged the effect of a bottle of hair dye.
Make an 0.25% solution, or thereabouts, by dissolving 10 grams of soap flakes in hot water and topping-up the resulting solution to 4 litres. That's roughly one ounce in a 12L bucket of water. The exact dilution is not critical but if you add much more soap you will finish up with something resembling a bucket of snot.
Soapy water appears to be lethal to adult RSM and MB. You can use it as a spray or a douche but you will need to reapply it in order to deal with any adults subsequently emerging from unaffected eggs. However, at the price I quoted, you can afford to be generous, even profligate, with the stuff. I sprayed and soaked every one of my 1200 or so plants. If it is cheap enough to dispense by the gallon you won't be tempted to skimp. I suspect that, had I lightly and/or selectively sprayed one of the much more expensive products, I might have observed much less effect than I did. The secret seems to be to hit the lot and hit 'em hard. If you can't see RSM or MB on a plant that does not mean that they are absent. Don't give them the benefit of the doubt or wait a couple of weeks to see whether your assessment was correct.
A handy tip is to save the unusable 'fag-ends' of your old soap bars and pop them into a jar of water. Then, when you want insecticide, you will have a useful 'free' supply to hand!
To deal with root mealy bug, immerse the whole plant, pot and all, into a bucket of soapy water. Leave for no longer than half and hour, then lift out and drain. You may have to repeat this in a week or so but do not overdo it. There appears to be evidence that roots should not come into contact with surfactants too often, irrespective of which, over-watering can be a potent cactus killer in its own right.
If you are of the 'catch 'em and kill 'em' school of natural control, and maintain that the plant bodies and/or roots should not be sprayed or treated, as at least one contributor seems to suggest, then the best of luck. Using tweezers to remove big fat juicy mealy bugs from the body of a cactus is one thing. Catching 'crawlers' or red spider mite in this way is quite another. In any case, if you imagine that picking off everything visible is sufficient then ease your plant from the soil a bit and see what is lurking on the underside of the body. You will often get a nasty surprise, even with ordinary mealy bugs. If you have the root variety then I would be very interested to learn how to eradicate them with a pair of tweezers.
Informative post. Thanks you....