Mealys....

[Murph]

Well, i finally upturned my pots and found all of my cacti infested with root mealys. After freaking out, i removed all soil and have been giving them a soap bath every day.
My question is, can i use a systemic pesticide that isnt a drench (just a spray) that will kill them, or does it have to be a drench?
And, how to i keep these guys away from the roots? I dont want to have to keep uprooting my cacti in the future, and i dont really want to keep buying pesticides for the rest of my cacti-growing life. Man i hate Mealys...

[parodias]

We have some indoor gardening stuff here which is called "plant pins" .. In fact they are pieces "cardboard" (carton) that are saturated with some systemic insecticide. Just "plant" one or two of those near the stem of the plant and wait ..
Conditions for success are a) soil must be moist for insecticide transport and b) plant must be growing as a stagnant sap stream will not transport nor take up any insecticide (which is the case for any systemic of course, no growing no effect!)
HTH

[YumAz]

I have several different kinds of cactus, they have a foamy stuff on them I was wondering what natural something I could spray on them to kill it

Answer

Your cacti probably have a pest called mealy bug.
Go to the drug store and buy a bottle of isopropyl alcohol. Also buy, if you don't have one, a 32 oz. capacity spray bottle, the plastic type is fine.
Fill with warmish water and mix in a couple of tablespoons of the isopropyl alcohol. Spray the plants thoroughly with this and it will kill the bugs. I like to rinse the plants after although the alcohol will do not damage because it evaporates quickly.
Once you have mealy bugs "on" the plants, they often are found in the soil too. Water the alcohol/water mix right through the soil as well.
If the infestation is severe you may have to unpot the plants, remove as much soil as possible from the roots and thoroughly wash the plants and the roots with warm water under the tap.
By the way, never use insecticidal soap on cacti. In time it burns the skin on the plants. I have not only had this experience myself, I've had reports from many hobbyists who had the same problem again and again.
(excerpted from)
http://www.theamateursdigest.com/sfsq&a.htm

[hegar]

Hello Murph,
you probably read what I posted about mealybugs. At first I tried warm - almost hot - soapy water. It did kill a substantial number of the pest, but left enough alive to start a re-infestation. Man, those guys are prolific breeders! Isopropyl alcohol will also kill them on contact. I have not used it as diluted as described by YumAz. What I do not know is, whether or not all stages of the insect will be killed. All it takes is the survival of a few of their tiny eggs and within a a few weeks or so you have the population thriving once again. Because my plants are out of the ground and not growing because it is almost winter here, I am now inspecting the cacti almost daily and manually killing any mealies I can find. I do have plenty of time to accomplish it because the cacti will not die anytime soon. For growing plants the best way is almost certainly the application of a systemic insecticide. But even with that method you might not get 100% eradication or some of the mealies could become resistant to the treatment. You can then switch to a systemic formula that is different and hopefully wipe them all out.
I have never noticed these critters on cacti before, but they seem to be a formidable foe that is exceedingly hard to get rid of once established.
I wish you the best of luck with your eradication efforts.

Harald