I was googling neem oil and came across a few interesting, scattered posts and links:
Neem Extract as an Insecticide
In India mainly, but also Asia and Africa, grows a tree all plant enthusiasts should be aware of, Azadirachta indica, commonly known as the "neem" tree, and a relative of mahogany. Extracts from the tree’s seeds contain azadirachtin, a relatively safe and effective naturally occurring organic insecticide. Let me preface the comments following, by reminding you that the terms "naturally occurring and/or organic" do not universally mean safe. Pyrethrums, rotenone, and even the very dangerous nicotine are all organic insecticides that should be handled with great caution. Neem extracts, on the other hand are very safely used in a wide variety of cosmetics, as a topical treatment for minor wounds, as an insecticide in grain storage containers, bins, and bags, and a whole host of other applications, and have extremely low mammalian toxicity. I'll limit this discussion to its use as an insecticide.
Neem works in many ways. It is effective both in topical and a systemic applications. It is an anti-feedant, an oviposition deterrent (anti-egg laying), a growth inhibitor, a mating disrupter, and a chemosterilizer. Azadirachtin, a tetranortriterpenoid compound, closely mimics the hormone Edison, which is necessary for reproduction in insects. When present, it takes the place of the real hormone and thus disrupts not only the feeding process, but the metamorphic transition as well, disrupting molting. It interferes with the formation of chitin (insect "skin") and stops pupation in larvae, thus short-circuiting the insect life cycle. It also inhibits flight ability, helping stop insect spread geographically
Tests have shown that azadirachtin is effective in some cases at concentrations as low as 1 ppm, but some producers use alcohol in the extraction of neem oil from plant parts which causes the azadirachtin to be removed from the oil. Some products touting neem oil as an ingredient actually have no measurable amounts of azadiractin. I use what is referred to either as cold pressed or virgin neem oil. You may also occasionally find it referred to as "raw" neem or "crude" neem oil.
Neem oil is most often used in an aqueous (water) suspension as a foliar spray or soil drench. Commonly, it is diluted to about a .5 to 2% solution, but the suggested ratio for use in container plant culture is 1 tsp. per quart of warm water. A drop or two of dish soap (castile or olive oil soap is best) helps keep the oil emulsified. The mixture is then applied as a mist to all leaf and bark surfaces and as a soil drench to the tree's root system. It should not be applied as a foliar spray on hot days or in bright sun as leaf burn may occur. Remember to agitate the container frequently as you apply and do not mix anymore than you will use in one day. Neem breaks down rapidly in water and/ or sunlight.
Some users of insecticides feel the need to observe the instant results of their efforts in order to be convinced of the effectiveness of what they are using. The application of neem derivatives does not provide this immediate gratification. There is virtually no knockdown (instant death) factor associated with its use. Insects ingesting or contacting neem usually take about 3 - 14 days to die. Its greatest benefit; however, is in preventing the occurrence of future generations. It is also interesting to note that in studies it was found that when doses were given, purposefully insufficient to cause death or complete disruption of the metamorphic cycle, up to 30 surviving generations showed virtually no resistance/ immunity to normal lethal doses, so it appears that insects build no ‘resistance’ to azadiractin.
I have been using neem oil for five years as both a preventative and fixative and have had no insect problems on my container plants. Applications of cold-pressed neem oil are most effective for use on mites, whitefly, aphids, thrips, fungus gnats, caterpillars, beetles, mealy bugs, leaf miners, g-moth, and others. It seems to be fairly specific in attacking insects with piercing or rasping mouth parts. Since these are the pests that feed on plant tissues, they are our main target species. Unless beneficial like spiders, lady beetles, certain wasps, etc., come in direct contact with spray, it does little to diminish their numbers.
Neem oil does have an odor that might be described as similar to that of an old onion, so you may wish to test it first, if you intend to use it indoors. I've found the odor dissipates in a day or two. As always, read and follow label instructions carefully.
Neem oil can be purchased from many net or local sources. My favorite brand is Dyna-Gro pure, cold-pressed neem oil. If you have trouble locating a source, you can contact me via the forum or directly.
http://http://www.discoverneem.com/neem-oil-insecticide.html
http://http://www.growsundews.com/neem_oil.html
---------- Post added at 08:35 AM ---------- Previous post was at 08:31 AM ----------
I haven't done anything with it yet, other than look at the ingredients and instructions. It does not mention having any
azadirachtin. So I'm not sure how effective it will be for aphids. I have no idea how to obtain azadirachtin (yet), either. I can easily try it on a capensis first.
Andrew, did you follow the recipe as listed in the instructions or did you dilute it? Did you spray the leaves only or not at all and/or the soil?
---------- Post added at 08:50 AM ---------- Previous post was at 08:35 AM ----------
I just googled Green Light and found their website. I then asked them right out, in an Email about azadirachtin, dish soap, and dosage for CP's.