The Dutch elm disease fungus, Ophiostoma ulmi, grows and reproduces in the xylem of elm branches and stems. The fungus blocks water movement to tree leaves, which causes the leaves to wilt and turn brown. Elm bark beetles (Scolytus multistriatus) use weakened and diseased trees to reproduce. Beetle offspring emerge from diseased elms and fly to healthy elms to feed; however, before leaving diseased trees, spores of the fungus attach to them. When these fungus-infested beetles feed on healthy tree branches, they make small wounds in the wood; the fungus enters the branch directly through these wounds. Once the fungus is in an elm tree, it can move through the root system of a diseased tree into the root system of adjacent healthy elm trees. Wilting and leaf color change are symptoms of Dutch elm disease that occur during the spring and summer, but usually start to appear one month after trees leaf out in the spring. Leaves at the end of large branches appear to be most affected. Dead branches without leaves may indicate mortality in the previous year. Dutch elm disease kills individual branches and eventually the entire tree within one to several years.