Pythium root rot produces less distinctive diagnostic symptoms that included root rot and dieback. Even trees that have appeared to recover are still at risk for infection by a group of opportunistic pathogens, members of the genus Armillaria . These fungi are the causal agents of shoestring root rot. There are hundreds of species of Armillaria, some of which are virulent pathogens and others of which act only as contributing factors to tree death. Although drought is usually considered the inciting agent that allows Armillaria to establish itself and infect, flooding has been implicated as a factor of Armillaria root rot in oak, chestnut and larch.
Flooding is but one of the many injurious factors trees face over the course of their lives.
Proactive maintenance of tree health is the best way to contend with periodic flooding. As the tree recovers, it needs to replenish food reserves. To increase tree vigor, the US Forest Service recommends application with a low nitrogen fertilizer, aerating the soil, mulching, and watering if soil conditions become excessively dry after the flood. Dead or cankered branches should be removed. Prune trees only when bark surfaces are dry or during the dormant season to minimize infection by opportunistic pathogens.