[Root and butt rots of trees: a well-kept secret] Root and butt rots are hidden tree diseases. During a long part of their life cycle, these pathogens are mostly invisible in spite of their catastrophic final impact on trees. In Quebec, data on wood volume loss caused by root and butt rots are sketchy. A report from the Canadian Forest Service divided forest loss caused by diseases from that caused by insects in Quebec to respectively 36% and 64%, without mentioning root and butt rots. In comparison with data from Ontario where root and butt rots have been studied, the percentage of losses caused by diseases is around 65%, which is the opposite of the situation reported in Quebec. Moreover, losses through root and butt rots in Ontario could be underestimated as they are often reported under defoliators or windthrows. Forest treatments may increase the impact of root rot pathogens. For example, pre-commercial thinning in conifer stands has promoted the development of root rot pathogens on residual trees with a result opposite to the one expected. By cutting these trees, we are creating a new ecological niche that does not occur naturally, i.e., stumps. These stumps are colonized by several fungi including pathogens. For example, thinning of red pine stands favours stump colonization by Heterobasidion annosum if these stumps are not treated. Spruces can become infected by Inonotus tomentosus if these trees are under stress, e.g., in a stand of high stem density or because they are planted on a low quality site. Finally, Armillaria root rot on stumps of hardwood may kill conifer seedlings planted nearby.