You may want to read some of my other answers and referenced sights. Here is a quick answer of just a few of the very many, natural and organic approaches. Remember, this is but a few. And remember, if you also use synthetic chemicals with these natural approaches, they tend to kill and put out-of-wack the natural, healthy systems of plant and soil life. Otherwise, the organic approaches will not be as effective because you are killing or altering natural, healthy processes by applying synthetic fertilizers or chemicals. Cornmeal fights all kinds of fungi. You will see some data if you click my name. Garlic tea (and sometimes you can mix in some pepper tea with a bit of ginger) will inhibit all kinds of bugs and diseases and fungi. Even skim milk diluted with water can be sprayed as an antifungal. Lots of plants and their extracts inhibit mosquitos and bugs. See some of my posts. Diatomaceous earth (d.e.) [food grade...that is important] not only will help handle fleas and roaches and such, but actually adds some great trace minerals to your soil. Read my posts on it. Adding amendments to your soil like molasses (dried or wet -- you can get dried molasses at most feed stores) will improve the microbe activity and go a long ways towards a better soil and mineral content. Other amendments include lava sand (the paramagnetic properties have a profoundly good effect on plants and soil --and, by the way, this is not an esoteric mystical thing, but a physics interaction well researched), greensand (ancient ocean deposits of all kinds of minerals...often found in different localities of the country), and most important!!...Compost. Soil is very much "alive" with billion of microbes and healthy soil in itself fends off pests and diseases and weeds. It is just a fact of nature that healthy, active soil helps to grow healthy, strong plants. Healthy strong plants handle stresses well and innately fend off disease and insects. Plants in stress attract disease and insects. It is a fact of nature. If something is weak, nature takes it out. This can even be applied to the human body and system. If it is in an unhealthy condition from lack of nutrients or from toxins or from antagonistic people, the stress sets up the body towards all kinds of ailments. It is nature's way. There are many, many other things that one can do to help control pests and diseases.