What are the plants?

tj

Neem IS a horticultural oil.....it is just plant based rather than petroleum based. Do your plants have any issues currently? There may not be a need to do or use anything. Neither is particularly prophylactic.

FWIW, all my houseplants summer outside and the only treatment they get returning indoors is a good spray down at the kitchen sink.

That clears that up. I am just wanting to avoid pests entering my home from box stores.

Something I wrote more than a decade ago about neem oil and how it works:

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. Neem is very safe for use around birds & mammals. 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 disruptor, and a chemosterilizer. Azadirachtin, a tetranortriterpenoid compound, closely mimics the hormone ecdysone, 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.

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pH is based on a logarithmic scale from 1 to 14. Where a pH of 7 is neutral, a pH of 6 is 10 times more acidic than a pH of 7. Many insecticides are sensitive to pH levels because of something called hydrolysis, which is a chemical process whereby larger molecule with insecticidal properties are broken (cleaved) into smaller (ionic) particles that may lack any insecticidal properties when they recombine with other smaller particles. How much effect hydrolysis has insecticides depends on the insecticide's chemistry, water pH, water temp, exposure to sunlight, and how long the mixture has been in the spray container.

Neem oil is susceptible to alkaline hydrolysis, which means that a pH greater than 7.0 causes degradation, so adjusting your spray water to a pH from 5.5 - 6.5 for neem products is beneficial; whereas some pesticides are affected by acid hydrolysis at pH levels below 7.0, so they should be mixed with water adjusted to pH levels from 7.5 - 8. In either case, the sooner you use the spray mixture, the more effective it will be. White vinegar or citric acid (from a wine-making supply store) are very effective at reducing water's pH.

Al

Your writing is so helpful, dry AND readable. Thank you for this -- it is just packed with data informed by experience! I learned some things I was not aware of, and now plan to test my tap water for pH level. Again -- THANK YOU, Al!

Thank YOU. I appreciate your evaluation and the kind words!

Al

Neem oil is a natural product made from the Neem tree. It is used to control pests and diseases in gardens and crops. Horticultural oil is a synthetic product made from petroleum. It is used to control pests and diseases in gardens and crops.

^^^ Sorry, but the above is not correct. Horticultural oil is any oil used for horticultural - plant growing - purposes. Hort oils can be both petroleum based or plant based (like neem) and are of more or less equal effectiveness. Vegetable or plant based hort oils are becoming more common as many gardeners steer away from 'non-organic' control methods, even though petroleum based hort oils are fully approved for organic gardening usage.

One interesting note is that cottonseed oil is reputed to have the greatest insecticidal properties of any of the plant based oils.

Colorado State extension has a good publication on horticultural oils and insect control: https://extension.colostate.edu/docs/pubs/insect/05569.pdf

And Wikipedia has a good explanation on the various types of horticultural oils and their recommended usage: https://en.wikipedia.org/wiki/Horticultural_oil.