I've never used neem oil as our area has an abundance of lady bugs and they think aphids are just decadent.
However I'm really replying because it seems neem was discussed here previously and someone pointed out it was poisonous or a carcinogen or something along those lines. Anyway definitely search this forum for neem and see what comes up.

I will, thanks Grizz!

OK, so I searched the site (I don't know how to just search THIS forum) but from what I have read it seems that it's safe! It has an odor that some find overpowering, and they say not to ingest it if you're pregnant, but say that the residue is safe. I saw nothing about poison or cancer, even in my google search.

So I'd still like to know if it will effect my system. Since it's topical and seems to evaporate fairly quickly, I'd like to assume it's not going to have a huge impact, if any. Thoughts?

Here is a link that might be useful: One of the sites I checked

I think the issue had to do with it leaching into your nute solution (vs traditional dirt gardening). I don't remember exactly.
To search this forum only, on the main hydroponics page, scroll down the page below the thread list. you'll see a search box and button and a preselected bullet that says "This Forum". Hope that helps.

Neem oil is VERY safe to use. It is a foliar spray so unless you use a garden hose to spray your plants, I don't see any perceptible amount getting into your nutes.

You can spray with Neem today and eat a tomoto from the plant tomorrow, though I would wash it.

Mike

Thank you Grizzman, that DOES help! And that was exactly my thoughts about it leaching and then being absorbed. I knew topically I could wash whatever residue was left, but my concern is absorption.

I'll keep searching. Thanks!

Yes, Neem is safe, especially because the main toxin azadirachtin is not UV resistant and degrades (is said to) in less than 24 hours. Thats the downside as well, as neem oil needs indeed to be applied more than once and preferably in 48h intervals to be effective. Also, it is more like a repellent and a reproduction inhibitor than a poison. Unfortunately it is not effective against thrips and some other more robust parasites. I generally recommend lowest doses with frequent foliar spraying.

I would not recommend any systemic treatment against insects with Neem products by default. Neither with hydroponics nor with soil culture. There are certainly some beneficial effects beyond the insect repellent effect, but efficiency of systemic treatment against insects is not proven, except for soil born parasites. Foliar spray (if applied by the book) on the other hand has proven to be effective and as it confirms my own experience, I would recommend to stick with it only.

To avoid any interference or "messing" with your nutrient solutions, simply avoid getting it into your system. Over cautious people may on top of that, make a treatment before the next nutrient change.

Only If using a more robust and non-sterile system like compost tea feeding as in "aquaponics WITHOUT fish", with drip to waste, in gravel-sand beds or similar, you may take the risk to add some Neem oil combined with a non toxic emulsificator directly into your system. This would be a systemic implementation. This option is a possibility, not a recommendation of mine -on your own risk and with best knowledge of possible consequences, of course. ;-)

Btw: young leaf sprouts of Neem tree as well as berries are part of some regional Thai cuisine ;-)

Note that Luc said "WITHOUT fish". I assume that emphasis was due to neem's toxicity to aquatic life. Something good to know, especially if you have a pond close to the system. It's been recommended that if you do have a pond close to the garden, you should consider sponge applications over spray.

I hope you don't mind, but rather than answer I'd like to make a suggestion. With aphids, you can easily remove them or just squish them on the plant. One way to remove them without squishing them with your finger is to wrap some masking tape with the sticky side out around a couple of fingers. Use it as a disposable sticky trap and throw it in your compost (or trash if you don't compost). It's generally not too sticky for the plant, but sticky enough to get the aphids, mites, or other bad little bugs you may encounter. No worrying about your nutes/pH or about clogging the stomata on the leaves with an oil.

Spraying leaves is a common technique and simply the most practical and effective method. From a certain (even low) number of plants you can't avoid it anyway. And, you don't only want to remove a few specimens, but have your crops completely free of them and protect not affected plants from invasion as well. Which clearly makes sense with a repellent, - doesn't it? and how would you control or inhibit the reproduction with such surgical intervention?

I have used Neem oil extensively in the past and leaves don't seem affected at all, even with frequent spraying. There are no reports of any problems with "clogged stomata" due to Neem oil, as far as I know, - except sporadic speculations about the possibility ;-)
In fact "Neem oil" used in relatively low doses in combination with an emulgator (preferably with a wetting agent) isn't that oily.

I guess the portion that MAY get into your system or nutrient solution is simply neglectable in most cases and hence wouldn't affect it.

An alternative (with regular aphid visits or an exposed/affected area), like here in the tropics is in fact protecting the crops with a smaller aphid net application or an aphid net house.

PS: the remark about "aquaponics without fish" was in fact a play upon words. It was meant as an allusion to the fact that the term aquaponics doesn't actually contain any hint about fish. One more "new term" that sounds cool but isn't very descriptive or from the shoulder at the end. A bit like bio or "bio-dynamic" that became "organic" eventually - which don't actually describe nor differentiate properly. Because these plants and products don't distinguish from other cultures as described, as others aren't less dynamic nor non-biologic and certainly not inorganic.

I know this is going a bit off-topic but the latest slogan I discovered displayed at the entry of some local super market that mainly provides imported food for expatriates was: "ORGANIC AWARE SHOP". Not sure (doubt it actually) that this was invented here in Thailand, but what the heck does that actually mean? Are they truly "aware" people, - or do they officially admit that they have finally passed the state of denial, regarding a movement they can't oppose for ever?! A new form of the "argument of conversion"? LOL

Just thinking loudly, ignore O.T. if not interested in some of my thoughts....