Check out this neat time-lapse video of our elm grafting process! Created by our very own J.W. Fillmore...and featuring American elm roostocks from our friends at Three Rivers Parks District Nursery.
Recently in dutch elm disease (DED) Category
Last fall I had the opportunity to join Mr. Don Willeke in observing the removal of a large 'Iowa State' American elm at his neighbor's house in the Dean Park area of Minneapolis. This large tree was planted in 1978, shortly after Don grafted it onto a wild American elm seedling. Unfortunately, the tree had developed major defects over the years (it had already been cabled and braced) and required removal for safety purposes.
Don is a local elm aficionado and has been "speaking for the trees" since the 1970s. He has been my host on many visits to the forest of elm trees (amongst other species) in and around his Dean Park home.
'Iowa State' was discovered and screened by Prof. Sandy McNabb at Iowa State
University from the late 1960s to early 1970s where it proved to be quite resistant to Dutch elm disease (DED) when inoculated with the fungus.
While not widely released (at least to my knowledge) this tree remains
an important reminder of those lucky escapes - native American elms with
high tolerance to DED. Unfortunately, the structure of this tree is less than ideal as it has a tendency to form weak branch unions due to inclusions and very acute angles of attachment.
In my ongoing efforts to make-lemonade-outta-lemons I worked with Don and Jay Linn from Log and Limbs Company (who was performing the removal) to collect some prime cuttings material for cloning of this now rare tree.
By the end of the removal process Don and I were able to collect some vigorous vegetative shoots from the very top of the tree, which I brought back to the University for propagation and inclusion into our elm program.
Now, weeks later, I transplanted some of the first rooted cuttings of 'Iowa State' and can now add this tree to the growing collection of elms at the University of Minnesota.
Plants are also slated for distribution to the USDA National Arboretum in Maryland for inclusion into their continuing work on the American elm.
This week's tree of the week is the London Plane Tree (Platanus x acerifolia). The London Plane Tree is a stately shade tree growing to a height of 70 feet tall. The mature bark is a stunning pale grey with exfoliating brown bark. The leaves resemble the look of a maple having a palmately lobed leaf. However, unlike a maple leaf, the London Plane Tree has a fussy back, giving it a unique character.
Being a zone 5 tree, The London Plane Tree is not commonly seen in Minnesota as it is not hardy to the northern climate. However, there are a few London Plane Trees scattered throughout St. Paul and Minneapolis. The slightly warmer temperature of the cities is often just enough for the London Plane Tree to survive the harsh Minnesota winter.
In the team tree fields, we have three varieties of London Plane Tree, Exclamation!™, Columbia, and Bloodgood. All three varieties grew extremely well this season! It was exciting to see the trees grow from small 4-6 foot whips to a sizable 1" caliper trees (left image). This fall, we dug out most the London Plane Trees to prepare to plant in root trapper containers next spring!
The image bellow shows two of the four rows of London Plane Tree at the nursery. The lush, 12 foot strips of grass like plants growing in between the rows of trees are cover crop that team tree uses in all fields to keep the soil as healthy as our trees. The cover crop is a mixture of millet and buckwheat, both fast growing plants. The cover crop is used to maintain moisture in soil, reduce weed population, prevent wind erosion, and finally, increase soil organic matter. Often times, nurseries keep the soil bare by continuously spraying for weeds throughout the season to reduce the competition for resources. However, the benefit cover crop provides for the soil far out weights the marginal decreased caliper growth.
The vigorous growth of the London Plane Tree is quite typical for the tree. The London Plane Tree is often used as street trees in warmer climates due to the vigorous growth and ability to withstand high compaction and atmospheric pollution. The number of tough tree species for urban situations is becoming less with the loss of American elm to Dutch elm disease and the more recent loss of Ash species to emerald ash borer. Both American elm and ash trees were extremely common street trees due to similar tough qualities the London Plane Tree has. With fewer and fewer street trees to withstand the tough street conditions, it is important to test the winter hardiness of different tough trees like team tree is doing with the London Plane Tree.
Elm trees on the research plot begin life as a cutting from an older elm tree. To get material to make new trees, we prune the old ones. Jonathan, myself, and Lara our volunteer cut off all of the lower branches from one plot of the elms. After taking the branches off, we took them to be processed.
Jonathan, Lara and I are all working our pruning technique. It is as much science as an art form, and to get material to make cuttings from, we are able to practice our cuts. We made a red permanent marker marking to outline the cut. When removing a limb, the aim is a cut that is perpendicular to the branch. The cut should be as close as possible to the collar of the branch without breaching it. The collar provides a physical and chemical barrier to disease entering the main stem of the tree, and nicking it or the trunk of the tree with a saw is the sure sign of a beginner.
During processing, we removed the new growth from the woody growth from last year. The newer the cutting, the more likely it will sprout roots. We cut the new growth into sections of around 6 inches, or the distance between an extended pinky and thumb (think "hang loose").
After they are in 6 inch pieces, we remove all but two or three leaves from the very top of the cutting. The bottoms of the cuttings are then dipped in a hormone solution that causes the cutting to sprout roots.
Fast forwarding 10 years, the elm trees in the plot are inoculated with Dutch elm disease. This disease wiped out much of the elm population, and now we are working to propagate the most resistant varieties. The trees that prove resistant to the disease are then trimmed down again, and another generation of elm trees is produced.
Kris Bachtell's presentation on New Elms for American Cities at the Minnesota Shade Tree Short Course was simply outstanding!
If you didn't get enough at the Short Course, take a look at handouts from the presentation, below!
Kris is V.P. of collections and Facilities at The Morton Arboretum in Lisle, IL.
- PDF of Slides (view online or right-click and select "Save Link As...")
- PDF Guides (view online or right-click and select "Save Link As...")
Researchers in Robert Blanchette's Forest Pathology Lab at the University of Minnesota have been working side-by-side with our scientists to inoculate selections with the DED fungus.
Outstanding specimens like this American elm located in Eden Prairie, MN may offer new options for trees in our increasingly threatened urban forests.
Photograph courtesy of Jeff Cordes - City Forester, Eden Prairie, MN