Will IMO help kill pest caterpillars?

I don't have space or permission for chickens, ducks etc. so need to use sprays and predators I suppose.

Brassicas (kale, Chinese vegetables) never survive in my yard because caterpillars just decimate them or damage them which stunts their growth. It's the only pest problem I have year round, along with aphids in summer. I'd be fine sharing the produce but they leave nothing for me; if I plant 50 kale seedlings throughout the yard in random spots I'm lucky to have 1 survive to adulthood.

I just read elsewhere that IMO spray can help annoy pests (hopefully caterpillars); is that true? How about chilli water spray? I don't want to harm good insects either.

Capsaicin in a spray bottle will do the trick for most damaging insects. You want to use a blender to make this spray and you need Habanero thru ghost peppers to get a best result.

Twenty or more habanero, serrano or ghost peppers in a blender with water to fill, blend to puree then filter through a paper coffee filter into spray bottle, spray plants and their surrounding soil. (you can dilute it more, to one gallon with water)

Here is a recipe from the SF web site.

Put 1/2-pound fresh habanero or Scotch bonnet hot peppers in the blender. (ghost peppers work super too)

Add 2 cups of water. Liquefy the peppers. (I use puree for two minutes)

Pour the mixture into a bucket. Use a long-handled spoon to stir in 1/2-gallon of water. (use a metal spoon, wood will soak up capsaicin and never let it go)
Cover the bucket tightly with aluminum foil and allow the solution to steep overnight.
Strain the mixture through cheesecloth or coffee filters into a 1-gallon container.
Add 1 teaspoon of non-degreasing liquid dishwashing soap and enough water to fill the container (milk jug works great). ( I like Palmolive dish soap for this part)
Cap it tightly and upend it several times to gently combine all the ingredients without creating suds.
The soap serves as a surfactant and increases the solution’s ability to adhere to the plant.

Funnel the pepper repellent into a plastic spray bottle.

Spray your plants generously with the solution to coat all surfaces thoroughly.
Apply it on a calm day during the morning or at dusk when the temperature isn’t expected to exceed 85 degrees Fahrenheit.
This will prevent the leaves from sustaining sunburn.
Homemade pepper repellent will kill any insects that you happen to spray it on directly, and will effectively repel newcomers even after it dries.

Repeat the application once weekly throughout the growing season.
Reapply it after rainfall in between weekly treatments.

As mentioned above (can't really stress this part enough)
You want to use this either early in the morning or about an hour before dusk (wet leaves in the south will mold if not dry before sundown) so you don't blister your plants leaves by sunburn.