wood ash- potash is something that peach, nectarines, apricots need more of that most trees to stay healthy. If a tree has too little it is very prone to leaf curl etc. It may or maynot be on the premise that a healthy tree is more capable of fighting off attack. As, I understand the problem, this is one disease you want to prevent as it is very hard to control once it starts. Since, the little varmints hide in the soil, maybe it is at that stage that wood ash is helpful, keeping their initial numbers down. I would love to know more about the article.