Copper sulfate is one.
https://geneticliteracyproject.org/2018/03/20/far-more-toxic...
Does it sound more organic if I call it ‘Bordeaux Mixture’ (before pointing at the all the people that died of copper poisoning)?
Say you have a fungus that eats at your corn, maybe there is another one that just eats that fungus but leaves the corn alone. Or maybe you have some insect that eats your wheat, and some naturally occurring compound exists that is bad for the exoskeleton of that insect; put compound (found naturally or replicated synthetically) on the wheat, insects will be sad/dead/gone, there ya go, organic pesticide.
Those natural, or, organic pesticides usually evolved with some specific target in mind, while man-made pesticides are more like chemo therapy: kill as much as possible without killing the produce we want. This has the downside that killing as much as possible actually kills things we don't want killed.
Obviously, and sarcasm apart, the difference is nuanced. Organic Farming revolves around what is apparently natural, and in practice there is just a list farmers must respect.
I've been paraphrasing myself a lot these days, only to avoid saying the same thing many times. But in my humble opinion as a farmer, Organic Farming is a secular kosher for urban people. It has nothing to do with better farming practices, and everything to do with a sense of control over purity - purity in terms of what is closer to the urban conception of what constitutes True Nature.
Better farming practices involves the rational use of pesticides, synthetic or otherwise, used only as a last resort and having always in mind the effects to Nature (soil, water and wildlife) and human beings (farmers and consumers). In Europe all of these considerations are contemplated under an official standard called Integrated Farming - Organic Farming's big sister, as I call it.
No one has been able to demonstrate health effects due to pesticide residue. Even studies purporting to show health effects for glyphosate do so at concentrations associated with handling the chemical in bulk, not at concentrations associated with consumption of residue.
Do more well-accepted organic pesticides have these kinds of problems with bulk handling? Because otherwise I feel like this should be reason enough to avoid it.