I have effectively used a combination of neem oil and dr. bronners soap sprayed on powdery mildew, works really well. Garlic, onion, chillis can all be blended up with water, or steeped and strained and sprayed as all purpose deterrent. Neem oil actually disrupts the life cycles of the bugs, they forget to eat and screw. If you want to get really gnarly with an invading hoard of the same type of bug, hand pick a bunch of them, toss em in a blender w/ water, make bug juice and spray it on your plants. soaking cig butts or some tobacco in water overnight and spraying that on bugs will definitely kill them, very potent stuff. Oh yeah, another good product to use is neem pellets, made from the pressing of the oil and sold as an organic fertilizer. Mix that into your holes and not only are you adding nice nutes, you are adding a slow release bug defense system that actually gets uptaken into the plant! There are many,many more organic pest solutions, dig into whatever problem you are having and surely you will find some organic way to deal.
However, my personal opinion gained through experience is that the best defense against bugs and diseases are HEALTHY PLANTS. Make sure that your babies have rich organic soil, ample moisture, and are generally well taken care of. Pests attack plants that have compromised immune systems and defenses, just like us humans. Grow big strong plants and the bugs will pick on someone else!