Swedish Columnar Aspen

Description:

This slender Swedish Columnar Aspen (SCA) is a broad leaf deciduous tree; a part of the willow family. Originally found in Europe and Asia, it has been cultivated in Canada. There are 5 young SCAs altogether in the bed that contains our particular subject. They share a willowy stature and close knit, upward sprouting branches. Leaves are simple, toothed, and diamond shaped. European Poplars are, "European poplar are much more coarsely toothed and sinuous," (New England Wild Flower Society). Their bark is a greenish gray, peppered with small white markings. Our subject of focus, who we'll call 'Bork' for convenience sake, stands out from its companions in a few ways (which you'll notice in the attached images): - Bork's height and bud growth are slightly below the average of its cohorts. - Bork's spread is also less than its friends, though its bark and branch appearance is similar. -Most significantly, Bork's foliage is much sparser and it's leaves are almost completely a dull brownish red, compared to the bright green and yellow of its fellow Swedes. Horticulture expert Kim Wickwire of Olds College suggested it may be Bronze Leaf Disease (BLD). A disease that commonly affects fast-growing Columnar Poplars according to Tree Care's Michael Allen (see links). Columnar poplars can be prone to other pests and disease, among them: carpenter worms, Hypoxylon fungal disease, and Cryptophaeria Fungal Canker Disease (Allen). While something has definitely been munching on the leaves, it is not rampant, and there are no irregular holes in the bark suggesting this pest. The bark is also devoid of yellowish-orange blisters that characterize the Hypoxylon and Cryptophaeria diseases. It would seem the most likely candidate for disease is BLD due to the brownish coloration of the leaves, with the rest of the tree appearing relatively healthy. However, there are some discrepancies in the diagnostics. BLD patterning usually begins in the base of the foliage continuing upward (James Burrow, Lead Integrated Pest Management, City of Calgary, video), and Bork's foliage is almost completely brown, which would suggest that it's had the disease for 2-3 years (it was planted in the summer of 2016 according to the accession notes on Histree). Furthermore, I did not notice browning under the bark, though there were some dead branches at the base of the tree. Not all of it's leaves show the springy green veins and dark border common to BLD (James Burrow). Poplars are also sensitive, according to the Lone Pine book, "Trees and Shrubs of Alberta", and as Allen point out fast growing trees often experience growth stresses. Accession notes from Histree state that it was 'drought stressed when planted; not watered that night; played catch up but look[ed] okay' when the whole plant was planted on 7/15/2016, which would add to the vulnerable status of the tree. A snow storm that blew in Monday, October 2nd, could have had further damaging impact on sensitive Bork. Also from Histree: Height: 395 cm Spread: 133 cm Circumference: 15 cm Diameter @ breast height: 4.77 cm Estimate of current year's growth: 2.2 cm

Habitat:

Bork lives in the recently installed Wetlands Treatment area of the Olds Botanic Garden. As mentioned in our assignment outline the Wetlands are home to diverse species and many trees are still in shock from recent planting, as our dear Bork is. This makes them more vulnerable to pest and disease. According to the New England Wildflower Society, "European poplar has a very patchy distribution in the U. S., and in New England is only recorded from Hampshire County in Massachusetts". Olds, Alberta, is North West of that range with a much colder, drier, windy climate that might add to the stress of this species. Bork shares its bed with 4 other SCAs, which all seem to be doing well. The soil is most, but well-drained with plenty of mulch on top, which Poplars like (Trees and Shrubs of Alberta, pg. 68).

Notes:

My diagnosis is that Bork has Bronze Leaf Disease, based on my observational and research data (though I welcome a second opinion!). BLD is a fungal disease is making a comeback in Alberta (Burrows), and once accurately diagnosed, I would alert Agriculture and Forestry. The disease spreads via spores washed/blown in the spring (and/or systemically), which are accelerated by moisture and warmth. The disease typically develops in summer showing symptoms in August. (Alberta Agriculture and Forestry). I would check the surrounding SCAs and prune any that show signs. Diseased branches can be pruned 20-30 cm into healthy wood. All tools must be thoroughly disinfected, and cuttings put in the garbage, as opposed to the compost where disease might spread. Because Bork's foliage, from base to crown, is about 80% brown, I would not recommend pruning off the disease, as it would not leave enough leaves for photosynthesis, and severely weaken and already impacted tree. If the symptoms of the disease become apparent in surrounding trees, Bork might have to be taken out completely. Citations: Bronze Leaf Disease Parks - http://www.calgary.ca/CSPS/Parks/Pages/P... Bronze Leaf Disease - Government of Alberta, Alberta Agriculture and Forestry, Corporate Services Division, Extension and Communication Services Branch, Alberta Ag-Info Centre - http://www1.agric.gov.ab.ca/$department/... Michael Allen, T. C. (2009, September 20). Standing tall. Winnipeg Free Press (MB). p. D5. Populus tremula L. https://gobotany.newenglandwild.org/spec... Wilkinson, K. (2010). Trees and shrubs of Alberta. Edmonton: Lone Pine.