The last thing you want to do is fill your garden full of toxic chemicals. It is counter-productive, the bugs get resistant to them, and you'll end up with more that it won't work on! Plus it kills beneficial insects too, and you run a risk of poisoning pets or even your kids, with this stuff around. Plus, who wants to eat food laced with pesticide? There are lots of things you can do to lessen the impact the smaller visitors to your garden may have, mostly preventative, but once they're are here, if they've gotta go, try to do the least harm possible
Ants won't walk across certain things. You can make a barrier with cream of tartar (yes, the one you bake with), red chili powder, paprika, or dried peppermint leaves. Two things that will actually kill ants are diatomaceous earth and borax. Be careful with borax, it will harm your plants.
This was my greatest challenge last year on my roses. They turned the leaves to lace. I was vacuuming them off, picking them off, burning them off, you name it. Finally found this solution:
Mix this together and spread it around the base of the tree affected.
Slugs, Snail, Earwigs
Kill them with kindness. Place dishes of beer around the garden, they fall in and die happy
Bugs that chew and suck, Mildew, Leaf Spot, Rsut, and Spore Disease
3 cloves garlic
Blend this and steep for 10 minutes. Strain. Dilute this "tea" with one part water to 4 parts mixture before spraying
Aphids, June Bugs, Black Spot, and Rust
6 rhubarb leaves
Steep rhubarb leaves in boiling water. Strain and stray. This is VERY poisonous to humans too, keep out of reach of children.
1 cup chopped horsetail
Boil horsetail in water for 20 minutes. Cool and strain. Spray as required
Red Spiders, and General Houseplant Pesticide
Soak onion trimmings in water overnight and wash affected leaves wth this. Soap sprays are also very effective. Garlic planted in a pot will keep red spiders and many other mites away