Five cultivars and two populations of wild-type seedlings of American elm (Ulmus americana), 3 and 4 years old, were examined for differences in their abilities to compartmentalize and resist infection by artificially inoculating with Ophiostoma novo-ulmi.Morphological characteristics of tree defence, often referred to as the compartmentalization of decay in trees model, were used as a conceptual framework, with particular emphasis on the limiting of tangential spread of infection within the xylem and barriers that limit spread outwards to cells formed after infection. To investigate the change in functional xylem over time, 3-year-old trees were assessed at multiple time points following inoculation for hydraulic conductivity. Three and four-year-old cut trees were placed in 0.1% w/v safranin O for 18 to 24 hr to indicate functional xylem. Transverse sections of the stained stems were used to calculate per cent of sap-conducting xylem area and the per cent of circumference conducting of first formed cells and later formed cells. At each collection time, trees were assessed for disease severity on a 1-12 scale, based on the percentage of permanent wilt in the crown. There was considerable variation between cultivars in disease severity and their capacity to localize and resist infection. "Prairie Expedition," which had the lowest disease severity rating in 2015 and the second lowest in 2016, consistently limited the spread of infection into newly formed xylem and had functional xylem around the entire circumference of the stem at 90 days post-inoculation. "Valley Forge" in 2016 had the lowest overall disease severity ratingand was the only cultivar to consistently limit the tangential spread of infection within extant xylem. This research identifies key characteristics that some cultivars have to resist and limit infection and provides new information that can be used in disease screening programmes to evaluate other cultivars and older plant material.

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Wind loading events vary in their intensity and degree of damage inflicted on urban infrastructure, both green and gray. Damage to urban trees can begin with wind speeds as low as 25 miles per hour, especially when those trees harbor defects that predispose them to structural failures. The tree damage triangle integrates the three main factors that influence tree failures during wind loading events, namely the site characteristics, the (wind) loading event and any defects of the trees in question. The degree of damage that trees experience is generally a function of these factors overlapping each other. For instance, when the potential damage from wind loading events is exacerbated by poor tree architecture and compromised site conditions, the likelihood of significant damage is realized. Two studies on the damage to urban trees and the predictability of damage are reviewed; one study is a longterm gathering of wind loading events and accompanying damage to trees while the other is a case study of one storm in one city on one day. Both studies revealed critical pre-existing conditions that left trees vulnerable to whole tree losses: large trees in limited boulevard widths and severed roots as a result of sidewalk repair.

Grass, intercropped with nursery stock, is beneficial to the long-term productivity of a field due to decreased erosion of topsoil and increased soil organic material. The primary disadvantage of using grass as an intercrop is supposedly due to a reduction in nutrients and water available to nursery stock. In the spring of 1999, Fraxinus nigra ‘Fallgold’ trees were planted in herbicide strips with no intercrop (cultivated soil), an intercrop of untreated ryegrass, an intercrop of mowed ryegrass or an intercrop of ryegrass treated with a growth regulator. Half of the trees in each treatment were irrigated and half were not. Growth measurements were taken over two, growing seasons. There were no significant increases in growth with the addition of irrigation with the exception of trees grown with an intercrop of growth regulated ryegrass where the addition of irrigation resulted in greater tree height. Trees grown with no intercrop had the greatest increase in both caliper and height. Trees grown with grass treated with a growth regulator and irrigated did not show significantly different growth from non-irrigated trees grown without intercrops. Trees grown with untreated or mowed grass had the lowest increase in caliper and height.

Pot-bound Tilia cordata Mill. and Salix alba L. ‘Niobe’ were planted in a Waukegan silt loam soil in June 2003 at the University of Minnesota TRE nursery in St. Paul, Minnesota. Before planting, the root balls of the container-grown plants were mechanically disrupted using one of three standard root pruning practices recommended to correct circling roots: scoring (slicing), butterfly pruning, or teasing. Root balls on the controls were left undisturbed. The trees were harvested in October 2004. Roots growing beyond the original root ball were counted and measured for diameter growth to assess the effectiveness of the root pruning techniques in encouraging root growth outside of the original root ball. All root disruption treatments resulted in increased fibrous root growth, but no mechanical root disruption method was significantly better than root balls left undisturbed.

Establishing the effects of planting depth on tree stability and growth is critical in understanding the role nursery production plays in planting depth issues at the landscape level. In this study, bare root Whitespire birch (Betula platyphylla var. japonica ‘Whitespire’), green ash (Fraxinus pennsylvanica), Snowdrift crabapple (Malus × ‘Snowdrift’), and bicolor oak (Quercus bicolor) were grown for 17 weeks in a container production setting with four levels of substrate over the first main-order root: 0, 5, 10, and 15 cm. Birch demonstrated the greatest instability of all species, leaning significantly more when planted at 0 cm than at 15 cm. In ash and crabapple, there were no significant differences in either the number of trees leaning or the amount of lean in all treatments throughout the study. Oak stems bent excessively, invalidating lean measurements. Stem caliper increase was significantly greater in ash planted 0 and 5 cm deep than 10 and 15 cm deep. There was no significant difference in stem caliper increase between planting depths in other species. Birch planted 0 and 5 cm deep had greater root volume increase than those planted 10 and 15 cm deep. Root volume increase in ash, crabapple, and oak did not differ significantly between treatments. Infrequent windthrow events were observed, but appeared random and apparently unrelated to planting depth. The perceived benefit of planting trees deep in containers to improve stability was observed in only one species (birch) at one depth (15 cm) and was at the expense of significantly reduced root volume increase.

Container production of ericaceous plants requires maintenance of a long-term substrate pH of 4.0 to 5.5. The objective of the study was to examine the effects of incorporated elemental sulfur, ferrous sulfate, and aluminum sulfate on long-term pH suppression in an acidic container substrate irrigated with highly alkaline water. ‘Northcountry’ blueberry liners were planted into a peat/pine bark based container substrate containing one of six different commercial amendments for pH reduction at three different rates of actual sulfur: 0.89 kg S/m3 (1.5 lb S/yd3), 1.78 kg S/m3 (3 lb S/yd3), and 2.67 kg S/m3 (4.5 lb. S/yd3). After fourteen weeks, only one elemental sulfur treatment had a substrate pH significantly lower than untreated substrate pH. Elemental sulfur particle size played a role in ability to control substrate pH.

Plants that have been grown in containers for a long period of time frequently develop roots that grow in circles, following the contour of the container in which they have been planted. This condition is commonly referred to as “pot-bound.” It is considered common knowledge that if a pot-bound plant is transplanted without any treatment, its roots will continue to follow the contour of the now-removed container. There are, however, a number of transplanting techniques that are intended to reorient the roots in a direction that will be conducive to helping roots to grow out of this potentially harmful situation. These techniques include: butterflying, or slicing the rootball into two halves before planting; scoring, or making inch-deep slices around the rootball at 90° increments and an X-shaped slice across the bottom; or teasing, where roots are manually pulled out of the shape of the container in a direction perpendicular to the stem. Severely pot bound Salixalba and Tiliacordata were treated with one of the three treatments previously listed or as a control and were transplanted into an experimental field and grown for two full seasons. After two seasons, the trees were harvested and the number and size of roots escaping from the pot-bound region were recorded. None of the treatments allowed roots of any size to escape the pot-bound mass more effectively than the control.