WW-03765     1993  

History of Dutch Elm Disease in Minnesota

Dutch Elm Disease in Wild Elms

Surprising to many, the wild elms are of value even in Minnesota

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Most of the information available on elms in Minnesota refers to trees located within communities. Little is known about our native so-called wild elm population.

Surprising to many, each of several varieties of wild elms are of value even in Minnesota, where they are not generally as large as in other regions of the country. The rock elm, for instance, was a highly desirable species that had historically been selectively harvested by farmers for buildings and later for ship building.

For better or for worse, there has also been an export market for the wood of various species of elm. It is widely suspected, in fact, that it was exported rock elm logs that carried the more virulent strain of the Dutch elm disease fungus to England about 1976. The transfer of this more virulent strain back to Europe resulted in catastrophic losses of elms in southern England. This aggressive strain then moved from there into mainland Europe, threatening more serious losses than previously encountered in those countries.

The slippery elm, also known as red elm, is another highly desirable exportable species. Red elm lumber is sold for veneer logs in the European market. Historically, many of these trees have been harvested in southern Minnesota. The wood of red elm is far more desirable and easier to veneer than the American or white elm. The American elm is, however, used for furniture.

Companies which export elm tree logs for use as veneer are especially concerned about the impact of Dutch elm disease, as it takes a long time to grow an elm to a size suitable for veneer.

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Rural data rare, disease impact extensive

In spite of the value of wild elms, very little effort has been expended in dealing with Dutch elm disease in rural areas. Even the accumulation of data on rural tree losses is inadequate to be certain of what has happened. There is no doubt, however, that the losses have been substantial.

In 1975 and 1976 the incidence of Dutch elm disease in the rural areas was determined in evaluations of random plots scattered throughout Minnesota. The distribution of these plots was skewed, with more being in the southern sector than in the middle third of the state. No rural plots were established in the northern portion of the state because of the paucity of elms in groups suitable for a plot.

Losses to Dutch elm disease were substantial, and the peak losses in 1977 paralleled the urban pattern (Table 8). In the southern sector, the research plots established had tree counts ranging from 17 to 63. Only a few large trees over 60 cm (measured at a height 54 inches up the trunk) were present. Six plots were established in the central region, with number of trees ranging from 12 to 76. Again trees more than 60 cm were uncommon.

Table 8. The incidence of Dutch elm disease in rural Minnesota in 1975-1977 was determined by tree counts in random scattered plots.

Southern Region:		Central Region:
Year	Percent	Year	Percent
1975	5.7	1975	0.9
1976	15.0	1976	11.4
1977	73.0	1977	23.0

The losses in urban communities in the same regions were significantly less. The comparable losses in urban situations were 2.7 percent and 8 percent in 1975 and 1976 contrasted to 3.4 percent and 13.3 percent for rural trees.

In a separate study, 19 randomly located plots were defined in 1979 in a band running from north to south through the middle of the state. In the 1979 baseline examination, the percentage of diseased elms averaged 14.3. By 1981 that average had increased to 28 percent. Actual incidence of Dutch elm disease varied greatly between plots, ranging from none to as high as 90 percent. The losses were highest in the south and least in the central sector.

Between 1979 and 1981, the percentages of Dutch elm disease on farmsteads with elms, from Mankato to Tracy in southern Minnesota, increased from 88 percent to 94 percent. By 1983, nearly all of the elms on those farmsteads were estimated to be lost, and by 1985 it was thought likely that close to 90 percent of the wild elms over four inches in diameter were probably lost.

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

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