Keep them guessing
Our most important defense against insects and disease is crop rotation - that is - moving types of vegetables from one place to another each year. That way, a bug that found the cabbages last year will have zucchini to work with this year -- and chances are that that won't be their cup of tea. Insects that we see we just pick off, and a bit of soap water does the trick on most diseases. Very simple and non-toxic - that's the way we like it.