History of Dutch Elm Disease in Minnesota

Minnesota seems to have been the
target of many attempting to sell the
latest cure for Dutch elm disease

A city councilman of one Minnesota city once confidently informed the University of Minnesota forest pathologist that the answer to Dutch elm disease was the systemic insecticide Bidrin, and that for a bit more than a dollar a tree the elms could be saved. His authority was a story in Readers Digest. Bidrin, a toxic material, would be delivered in sealed plastic containers with recommended cautions of avoiding contact with the chemical. A user would have to guess the health of an elm to judge the amount to use. Too much would severely damage or kill the tree; not enough would fail to kill the bark beetles until after they had moved on and inoculated other trees. The University never recommended its use in Minnesota. Ultimately a brief news release by the U.S. Forest Service announced that Bidrin was not effective.

A more recent control candidate was the bacterium, Pseudomonas syringae which has been known for some time to inhibit the growth of many fungi. Many species of bacteria are inhibitory to fungi, but claims and publicity for this approach to dealing with Dutch elm disease went far beyond both the available data and the opinions of the people involved in its testing. Some of the promoters, overly anxious to solve the problem, suggested that a group of scientists could solve Dutch elm disease in two years if turned loose on the problem, and that the bacterium was one of the answers.

Influenced by early reports on its potential, people were anxious to obtain the bacterium and inject their trees. It was claimed that even a tree with 45 percent of its crown wilted could be saved. The statement was made “that the results are too good to be true.” Publications offering data on the effectiveness of the bacterium were scanty, however, and it was difficult to determine just how well the bacterium performed, especially on mature shade trees.³

A major company became involved in the work on Pseudomonas syringae and invested resources to learn whether injecting the bacterium into infected elms would indeed save those trees. They also worked on related procedures for manufacturing the bacterium, storing it, and bioassaying trees that had been injected so as to determine whether the bacterium remained in the trees. There were also problems to overcome in selecting the correct strain of the bacteria, as only certain strains had a high level of activity against the particular fungus that caused Dutch elm disease. Although there were some reports indicating some reduction in disease symptoms in the year of injection, most of the treated elms did not recover and died. Enthusiasm for this control has disappeared.

The principle of using bacteria to reduce the activity and damage caused by a pathogen is, however, valid. Undoubtedly, in the future we will learn how to use living antagonists to control diseases such as Dutch elm disease, but considerable research on the subject is still needed.

Other suggestions for biological controls included using pheromones, a sex attractant, to draw the beetles carrying the fungus into traps containing cacodylic acid to kill them. The U.S. Forest Service ran major research projects in Colorado, Detroit and Minneapolis to evaluate pheromone traps as a way to reduce beetle activity in an area. In Colorado, entire cities were used to evaluate the effectiveness of these traps, with multiple rows of traps placed around the community to be protected. The researchers concluded that the system was only useful for monitoring beetle populations. The reduction in Dutch elm disease was not significantly better than in areas without traps.

Trees injected with cacodylic acid are killed by this arsenical compound, and beetles which are attracted to these trees will not survive. Another compound, potassium iodide, was also found to be potentially even more effective. A forest pathologist in Illinois demonstrated its value even before research on cacodylic was begun in Minnesota. But despite its potential, EPA approval of potassium iodide was never obtained and it has had only limited use in control programs. It instead became an example of a potential research find which never progressed beyond publication of an academic paper: the bridge between research and application often is either not present, or cannot be crossed for any number of reasons.

Minnesota seems to have been the target of many attempting to sell the latest cure for Dutch elm disease. A product called “Elm Arrestor” was sold in at least four states, including Minnesota. “Elm Arrestor” actually, as far as we know, had different compositions over a number of years, and there was no data supporting the efficacy of any of its various formulations. At different times its active ingredients were mercuric chloride (.12 percent) and methyl alcohol (95.65 percent), or inadequate amounts of Arbotect.

Antibiotics called aureofungin and KT were tested in Georgia, Kansas, Kentucky and Minnesota. On the Minneapolis campus of the University of Minnesota, treated trees that were known to be infected with Dutch elm disease died. The value of these antibiotics has not been supported with data. Some of the same people involved with promoting the antibiotics later obtained EPA approval of a product labeled as Phyton-27, again with no data supporting its value for the control of Dutch elm disease.

There have been claims for a product called Fungi-sol [2-(2 ethoxyethoy) ethyl-2-benzimimidazole carbamate]. No data on its effectivness is known to have been published, and only the company’s statement that the chemical is effective against Dutch elm disease is available.

In the early 1970s a product called “Treegard” was proposed as an answer to Minnesota’s elm problem. The promoter stated that over 1,000 elms had been treated and every one of them had survived. This was followed by “Elm Guard” (sodium salt of 2, 2'-methylenebis (4-chlorophenol) [dichlorophenl] which was demonstrated to be ineffective.

In the mid ’70s, the fungicide BRW-101, a derivative of vanillin 3-methoxy-4-hydroxy-5-chlorotoluene, was proposed for injection into trees with Dutch elm disease. The University of Minnesota injected 63 trees with this compound, again without any success in saving the trees.

Another material for injecting diseased elms was offered as M-62. Again, in spite of some positive statements about its ability to save elms from Dutch elm disease, there were no supporting data.

For many years copper nails have been recommended as the solution for many tree problems. Copper nails are actually toxic to the tree, and the copper is unlikely to be sufficiently distributed in the tree to be effective against a fungus. In fact, both copper and zinc nails have been promoted for the control of Dutch elm disease, though it’s difficult to understand why people would expect four rows of nails at three-inch spacing at a convenient height to have impact on a fungus.

Other proposals

An interesting approach to reducing beetle populations was suggested to be the parasitic wasp Dendrosoter protuberans, which supposedly will search out and parasitize larvae. These wasps were imported from France. The suggested plan was to release about 5,000, obtained from Michigan State University, along the Mississippi River. Rumors expanded that release to boxcar size loads. The release is not known to have ever occurred. Where they were introduced in other parts of the U.S., it was found that the wasp parasitized larvae under thin barked portions of tree. The important overwintering population in Minnesota survives under thick barked portions of the tree. The idea has not led to any major known effort in control here or elsewhere.

Another unusual proposal came from a florist and an allergist in Michigan. Hearing that the fungus kills by causing the tree to plug its own vascular system, they developed a decongestant liquid which they suggested could unplug the tree’s water transport system. They did receive national news coverage for their idea.

A dentist recommended mineral supplements, so the tree would be healthier. The Dutch elm disease fungus will, however, do as well in a healthy as in an undernourished tree. A medicine man from a South Dakota reservation suggested that St. Paul pay him $1 million to inject their elm trees with an unspecified ancient Indian medicine. From New Ulm, Minnesota, came a suggestion to use a mixture of carp, seaweed, and other ingredients. And “pyramid power” would cause bark beetles to veer away from elms, it was suggested, if a properly constructed pyramid was placed in the stand of trees to be protected. Another proposal prescribed seven applications of giberrellic acid mixed into other chemicals, along with background music and a high frequency emission from a tweeter. Supposedly two cities had contracted to have over 150,000 trees treated by this process.

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