The label should list any restrictions. Different brands of Neem have different concentrations of the oil so while one concentration might not hurt anything, others may burn leaves and kill beneficials.

Dave

Good points aniaja - so what pests specifically Don? And which type of mildew? Neem is a contact pesticide only so only works on some pests and only when sprayed directly on them but it can harm some beneficials with even indirect contact. Plus it has very limited effect as a fungicide.

Too many times inexperienced gardeners think that just because something is "organic" it does no harm. That isn't true. Organic controls can be abusive just as easily as synthetics.

Dave

I've found neem oil to be fairly safe and effective for many pests (including beetles and mites) on most plants. I used 1 ounce of 100 percent unadulterated neem oil mixed with a few drops of Ivory soap in a gallon of water. I don't spray open blossoms and I only spray plants at dusk to avoid hurting pollinators. Never spray in direct sunlight to prevent burning due to photo sensitivity.

I've heard that a non-toxic oil, e.g. vegetable oil, helps with mildew. A teaspoon of it in a pint of water, well shaken. I suspect neem oil might work not because it is neem, but just because it is oil. In any case, neem oil is not the agent of choice in mildew prevention.

I don't think neem is a contact insecticide, as in, kill-on-contact. The insects actually have to eat it.

Neem doesn't have to be ingested to work Dan. In fact ingestion is usually the last and slowest method of delivery. The oil suffocates simply by coating soft bodied insects and can be absorbed through the non-shelled part of the skin of other insects (and people) and prevents hormone function and blocks neuro-synapses. Scientific research into its long-term effects lags simply because there
are too many different active substances in neem oil and every insect
species reacts differently to neem insecticide.

So used inappropriately or excessively there are potential negative side effects.

Dave

I read the label - several times. 99% of products do not like to mention their problems, the 1% that do are not around long....

Using it for spotty mildew, cabbage lopers and cucumber beetles.

Well, the active ingredient in neem oil is azadiractin. (Though there are others as well.) This is what the BPIA says about it. http://www.bpia.org/biochemical-biopesticides/insect-growth-regulators/

"Azadirachtin is one of the most widely used botanical insect growth
regulators. Because of its structural resemblance to the natural insect
molting hormone ecdysone, azadirachtin interrupts molting,
metamorphosis, and development of the female reproductive system.
Immature insects exposed to azadirachtin (mainly by ingestion) may molt
prematurely or die before they can complete a properly timed molt. Those
insects that survive a treatment are likely to develop into a deformed
adult incapable of feeding, dispersing, or reproducing.

Since beneficial insects, predators, and pollinators do not feed
directly on the treated foliage, biopesticide insect growth regulators
are considered “soft” on beneficial insects such as honeybees, lady
bugs, green lacewings, and the parasitic wasps."

So ingestion might be the last and slowest method of delivery, but it sounds like that's how it usually works.

"I read the label - several times. 99% of products do not like to mention their problems, the 1% that do are not around long...."

If you truly believe that then it is probably best to not use anything on your garden food. Federal regulations on pesticide labeling are so over-whelming and so specific that the label usually ends up being bigger than the bottle the product is in.

You don't mention the brand you are using but I pulled up the labels from the three common brands and every single one of them lists hazards to humans and domestic animals, environmental hazards, first aid, precautionary warnings, etc. including warnings about the hazards to bees and other beneficial insects.

http://www.bonide.com/assets/Products/Labels/l024.pdf

http://www.biconet.com/botanicals/infosheets/70NeemOilLabel.pdf

http://www.fertilome.com/ProductFiles/40712%20Neem%20Approved%2005-15-12.pdf

The primary ingredient in the product sold for home garden use is 40-70% Clarified Hydrophobic Extract of Neem Oil. Azadiractin is but one component of the tree Melia azadirachta L. foliage and bark. The extraction process used determines how much of that particular compound remains in the oil once processed.

Dave

And returning to the OP's initial question, the labels also list species with known sensitivities to Neem compounds.

My grapes seem to be sensitive to neem

Neem oil could burn, use it in the evening

The only neem oil worth using is the 100% it must have the ingredient Azadiractin. It will say if it has somewhere on container most times on the front. If you use too strong a dose it could burn leaves depending on what plant., so it may be best to first test an out of the way portion of plant. Go easy on the dose first till you know.

Has anyone here used Neem oil as a systemic soil drench for indoor plants? I am battling scale and trying not to have to throw plants out.

Can you scrap-off the scale? That and alchol are the best.

I've heard of neem being used as a soil drench, but be aware that the active ingredients break down pretty quickly in the soil. After a week it is pretty much gone.