Answer: You are asking an interesting question. In some cases a healthy soil life will be able to displace harmful bacteria and so on. An improved soil structure due to adding ample amounts of organic matter will also allow the soil to hold healthier amounts of water and air. All of these factors would also contribute to healthier root growth and overall plant vigor making the plants less susceptible to disease in general. Some plants are of course more likely to develop root rot type problems, and some such as rhododendrons are very susceptible especially if planted in a heavy clay soil that does not drain well. Any efforts at improving the soil structure and in selecting plants suited to the native soil will be more likely to succeed. Finally, if you are composting at home, it is very difficult to build a pile that will reach and hold or maintain the extreme heat needed to kill off many diseases -- the piles are usually just too small. For this reason it is important to avoid adding diseased material to the pile. This is a routine precaution that should be taken to minimize the risk of introducing those problems into the compost and spreading them around the garden when the compost is applied. So in answer to your question, it has to be helpful, but whether or not it will eliminate it depends on a wide range of factors. I am so sorry you are experiencing problems with this, it is certainly disheartening.
I apologize for the delay in answering your question.
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