Pathologists investigating the recent death of many oak trees in northern California have concluded that the problem is due to a new plant disease, dubbed sudden oak death (SOD), caused by the fungal pathogen Phytophthora ramorum. While not disputing that P. ramorum is involved in the final demise of many oaks, there are a growing number of experts who do not agree that this pathogen is the fundamental cause of the decline. They point out that most of the dying oaks in SOD-affected forests show no expression of P. ramorum. Instead, they suggest that acidic conditions create mineral imbalances and deficiencies in soils that weaken the trees, raising their susceptibility to secondary pests and pathogens. Here I present evidence that, due to fire suppression, there has been progressive acidification of oak forests, leading to greater incidence of disease. This helps us understand both why the SOD phenomenon is occurring now and what can be done to solve the problem.