WW-03765     1993  

History of Dutch Elm Disease in Minnesota

Success Stories, and Failures Too

Emphasis should have been on saving the largest possible population of elms, many of which were 60 to 80 years old

---

Tree losses in Minneapolis have been previously presented to show how effective the control programs were and how, even with a late start, it has been possible to save a large proportion of the elms (Table 3). The Minneapolis record would have been even better were it not for the drought conditions of 1976 which led to massive beetle attacks that fall, and if they had not had major problems organizing sanitation programs in 1977. It took a great deal of effort to find enough qualified contractors to remove the large number of trees that had to be dealt with in that year.

Minneapolis is not the only city to effectively deal with Dutch elm disease. A very similar story can be told for Robbinsdale, a northern suburb of Minneapolis. It is assumed that their total number of elms prior to Dutch elm disease was about 8,000. As was true for other communities, their losses were minimal until 1976. (Table 6)

Table 6. Controlled annual elm tree losses in Robbinsdale, presented as an example of a Minnesota city that dealt effectively with Dutch elm disease.

Year	Number Lost
1972 1973 1974 1975 1976 1977 1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988 1989 1990	7 unknown 42 64 493 995 514 188 108 223 153 115 170 149 105 76 116 220 260

In 1977, for the same reasons discussed previously, the incidence of Dutch elm disease in Robbinsdale jumped to 995. With state funds and improved management of the program, losses dropped to 514 in 1978. Since then losses have been fewer than 260 each year. Obviously the sanitation program was effective and the city has saved many of its elms.

Entire streets were quickly denuded of their mature shade tree elms because property owners and municipalities failed to recognize the presence or the seriousness of Dutch elm disease. Improved disease indentification techniques were one positive outcome of early control activities in St. Paul, Minnesota.

In an unfortunate contrast, St. Paul bore the brunt of the disease attack. There were many factors that caused St. Paul to be further down the road of disease progress than other cities. This included the fact that the fungus was introduced to St. Paul early, around 1960 (and possibly earlier if the existence of some circumstantial evidence is to be believed).

The more rapid development of the disease in the southeastern section of St. Paul was in stark contrast to what happened elsewhere in the state. In this portion of St. Paul there were large concentrations of wild elms that were difficult to access because of the river and adjoining lowlands. Periodically for years the elms and other species suffered extensive flooding which provided many dead and dying elms where bark beetles developed large populations to spread into adjacent areas of St. Paul and the suburb of South St. Paul. One of the major disposal sites was also located in this same area, not far from Pigs Eye Lake which is part of the Mississippi River Bottom environment. Elm debris hauled to the dump was supposedly covered daily, but daily drives by this site clearly showed that the debris was not covered completely and that beetles had no problem escaping from the site.

The political climate in St. Paul also worked against control. The city had a treasurer who was reluctant to spend money on Dutch elm disease, and indeed received many letters from the public supporting his inclination to not waste money on trees. At that early stage many people failed to appreciate what was in store.

Researchers at the University of Minnesota warned St. Paul officials that to do nothing would still be costly, because hazardous dead trees had to be removed. The University had also emphasized that St. Paul’s practice of using more salt on their streets in the winter than was customary for other cities was contributing to the numbers of dying and dead elms throughout the city. In traveling between metropolitan area cities drivers were aware of a safer feel of driving on St. Paul streets, however the salt was damaging elms, especially along main thoroughfares and at intersections.

A few years ago it was pointed out to then St. Paul mayor George Latimer, that he would go down in history as being mayor when all of St. Paul’s elms would be gone. It was unfortunate for him because he was in no way to blame. The stage had been set and the disease well entrenched before he took office. In fact, under his guidance, St. Paul made a heroic last effort to save the situation. Despite budgeting $3.7 million to fight Dutch elm disease, St. Paul’s cumulative losses had already climbed to 28,000 trees, with an even higher 35,000 future projection. In fact, the city’s loss of elms passed 50,000 that year.

Prior to 1977 the city of St. Paul had 105,941 elms and had officially lost 46,754 or 44.13 percent of them. The losses dropped in subsequent years, largely because there were substantially fewer elms but also because of better sanitation. (Table 7)

Table 7. St. Paul continued to lose elms after the disastrous year of 1977, though at a much lower rate because there were so many fewer elm trees left, and because sanitation efforts improved.

Year	Number Lost	Percent Lost
1978 1979 1980 1981 1982 1983 1984 1985 1986 1987 1988	15,076 6,069 3,746 5,561 4,029 4,627 7,461 4,331 2,348 2,679 3,029	14.23 5.73 3.54 5.15 3.80 4.37 7.04 4.09 2.22 2.53 2.86
Total	58,956	55.56

In effect, St. Paul served the state as a testing ground for learning what to do to control Dutch elm disease, and from this standpoint aided all other Minnesota communities. For instance, spraying with methoxychlor in the spring was tried, only to learn that there were more problems than benefits. The city tried benomyl (the insoluble form), for which there had been claims of great success, only to learn that it was a waste of money.

St. Paul also learned early that detection was the achilles heel of their control program. When people who were selected for survey work could not even properly recognize elms, and marked ash and poplars as elms, detection efforts obviously suffered. But the failure demonstrated how important it was to hire people who knew something about trees and cared about what they were doing.

St. Paul supported early work in improved identification techniques, leading to an effective aerial detection system using 35 mm photography and a helicopter. St. Paul also learned early about the problem of spread through common root systems and tried, though unsuccessfully, to develop techniques to stop this means of spread.

Despite the magnitude of problems in St. Paul, the city did save a portion of their mature elms, and a planting program was begun to help the urban forest recover.

Many in Minnesota considered new planting to be a control measure for Dutch elm disease. This was very unfortunate. The emphasis should have been on saving the largest possible population of elms, many of which were 60 to 80 years old. It will be a long time before any new trees reach the size of these mature elms. A basic principle overlooked by many is that it is better to save what you have, what is already established, than hope that the newly planted will replace what is being lost.

---

In Partnership...

Produced by Communication and Educational Technology Services, University of Minnesota Extension.

In accordance with the Americans with Disabilities Act, this material is available in alternative formats upon request. Please contact your University of Minnesota Extension office or the Extension Store at (800) 876-8636.