Relative importance of root grafts and bark beetles to the spread of Dutch elm disease

Root-graft transmission of Dutch elm disease (DED) is sometimes ignored in both research studies and city programs to control DED. Our results indicate that elms adjacent to 1-, 2-, or 3-year-old stumps have a disease rate three to five times higher than elms not adjacent to stumps. We conclude that in Detroit, which has elm plantings typical of many United States cities, root grafts were probably responsible for more than 50 percent of the DED transmission in 1973.