Disease and pest management. The Container Tree Nursery Manual. U.S. Department of Agriculture Agric. The water mold fungi, species of Pythium and Phytophthora, are commonly occurring pathogens that cause serious root diseases in many plants. Although both of these fungal genera have been consistently linked to root rot of ornamental container stock, only Pythium is a serious pest of forest tree container seedlings.
All seedlings are susceptible to root rots caused by water molds.
Water mold fungi cause wilt symptoms, followed by chlorosis and stunting. Water molds are so named because they have motile spores that swim in water and therefore thrive in damp soils. Unlike many other fungi, they have no airborne spore stage. Both Pythium and Phytophthora are favored by wet, poorly drained media and cool temperatures. These root rots are more easily prevented than controlled.