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- Author or Editor: Michael A. Arnold x
Interest in chemical modification of root systems of container-grown trees has increased in recent years with more widespread recognition of implications of root system architecture of container-grown trees on subsequent landscape performance. Initial research on Cu-based latex materials for application to interior container surfaces to avoid circled, matted, and kinked roots at container wall: media interfaces began with small forest tree liners in the late 1970s and early 1980s. Transfer of this technology to horticultural crops followed from the mid-1980s to the present. Testing has spread to a wide range of temperate and tropical landscape trees, shrubs, herbaceous annuals and perennials, interior foliage plants, and vegetable transplants. Inhibition of root elongation after contact with treated container surfaces is via a mild Cu toxicity, frequently resulting in a stimulation of lateral root proliferation proximal to the inhibited root tip, but responses vary with species, cultivar, media composition and pH, and Cu concentration and formulation. Early reports on root architecture effects were predominantly qualitative in nature. Quantitative studies on root architecture within treated containers have been less consistent in responses among species. Improvements in root regeneration, shoot growth, and water relations during post-transplant field establishment of trees grown in Cu-treated vs. non-treated containers have been documented for several species. Ecological (Cu leaching potential), technological (new applications), and economic (profitability) questions have arisen with increased use and availability of Cu-based container treatments and will be discussed.
Shumard oak (Quercus shumardii Buckl.) were grown in 2.3-liter (#1) containers painted on interior surfaces with Spin Out™ (100 g Cu(OH)2/liter, or not. Seedlings were transplanted to the field and root observation boxes in June and October. The effects of two mechanical root-pruning techniques, traditional (cutting roots on exterior rootball surfaces) and butterfly pruning (splitting and splaying the rootball apart), to correct circling roots were compared with Spin Out-treated seedlings. Only the Spin Out-treated seedlings and fall-transplanted nonpruned controls had a net increase in height and caliper after 2 years in the field. Few roots >1.5 mm in diameter were severed in June with mechanical pruning techniques, while butterfly pruning severed roots up to 8.5 mm in diameter in October. Root regeneration shifted from predominantly small roots ≤0.5 mm in diameter in June to roots of between 0.5 and 1.5 mm in diameter in October. Spin Out-treated seedlings regenerated substantially more roots with diameters <1.0 mm at both transplant times. While midday water potentials were similar among treatments, Spin Out-treated seedlings had the least negative predawn water potentials, suggesting better recovery from midday water stress, particularly following October transplanting.
Quercus shumardii Buckl. seedlings were grown for 3 or 7 months in 2.3-liter black plastic containers. Containers were either treated or not on interior surfaces with 100 g Cu(OH)2/liter latex carrier. Trees were transplanted in summer or fall to quantify post-transplant responses to mechanical correction or chemical prevention of circling roots. Four treatments were used at each transplant date; nonpruned seedlings from Cu(OH)2-treated or nontreated containers, and seedlings from nontreated containers in which two mechanical root pruning techniques were used, traditional severing of circling roots on the rootball periphery or splitting and splaying the bottom two-thirds of the rootball at transplant (butterfly pruning). Traditional root pruning severed more small-diameter roots (≤0.5 mm), while butterfly pruning severed more large-diameter roots. During the first 21 days following transplant most root regeneration was via elongation of intact root tips. Cu(OH)2-treated seedlings regenerated substantially more roots ≤1.0 mm in diameter and a greater root mass than mechanically root pruned or nonpruned seedlings. Both corrective mechanical pruning techniques resulted in greater predawn water stress during immediate post-transplant (21 days) establishment in October than seedlings chemically treated to prevent circling root development. Treatments that severed more roots and/or removed greater root mass were associated with decreased field performance and increased post-transplant water stress. Increased numbers of small- to medium-diameter new roots were associated with reduced post-transplant water stress and improved post-transplant shoot growth. Nonpruned and traditional root pruned seedlings grew little during the first two post-transplant growing seasons regardless of transplant date. Butterfly pruning resulted in severe dieback of shumard oak seedlings. Cu(OH)2-treated seedlings were the only ones to exhibit a gain in height or stem diameter after 2 years in the field.
Plant trialing and promotion programs have become popular in recent years with many state and some regional programs emerging. Successful implementation requires considerable labor, facilities, and monetary resources for evaluation of large numbers of taxa over several years to ensure that plants are well adapted to the region of interest. Research and development funds and cooperator commitment to trialing programs can be limiting during the early years of these programs prior to production of tangible benefits. Dedicated facilities for program activities are usually not available. Mechanisms for development of facilities and procurement of labor to augment trialing program resources, while enriching undergraduate and graduate teaching and research programs, will be presented.
Pilot trials were conducted to explore the potential for use of Helenium amarum (Raf.) H. Rock as a bedding plant in Texas. Bitterweed is an annual wildflower native to the eastern U.S. It occurs on disturbed waste sites, along railroad tracks, roadsides, and in heavily grazed pastures. Bitterweed varies in form from a 15-cm-tall spreading mound to an upright oval crown 60 cm tall. Early growth is in a rosette form. Later foliage is bright green, highly dissected, and attractive. Profusely borne yellow single daisy-like flowers occur from spring to frost, peaking in late summer and fall. The species can survive intense drought and heat. Production responses were tested in 0.06-, 0.13-, 0.16-, and 0.51-L containers in the greenhouse during Summer 1998; then seedlings were transplanted to landscape beds and monitored through fall 1998. Other seedlings from 0.13-L containers were planted to the landscape to determine spacing requirements. Plants were also grown in an outdoor nursery in larger 2.3-L containers to test responses to pine bark- and peat-based media. Seedlings from 0.16- and 0.51-L containers were more effective throughout the growing season in the landscape than seedlings from 0.06- and 0.13-L containers. Seedlings grown in 2.3-L containers in a 4 pine bark: 1 sand media were larger, flowered more rapidly, and reach a marketable size in a shorter time than seedlings grown in a peatmoss-based media.
Five species of trees, Fraxinus velutina Torr., Pistacia chinensis Bunge, Platanus occidentalis L., Quercus virginiana Mill., and Ulmus parvifolia Jacq., were first grown in 0.45-L conventional black plastic liner containers, then transplanted to 25-L black plastic containers and grown to a marketable size. The same species were grown in similar-size, open-bottom, air-root pruning, cylindrical, aluminum (Accelerator) containers filled with the equal volumes of media. Plant growth characteristics, root-zone temperatures, and media moisture status were measured. Growth of Q. virginiana was reduced in Accelerator liner containers compared to conventional black plastic liners. Accelerator liners did eliminate circling and deflection of roots at the bottom of the liner containers. Growth of U. parvifolia, F. velutina, and Q. virginiana were similar in the larger 25-L Accelerator and black plastic containers, while growth of P. chinensis and P. occidentalis were greater in Accelerator containers than in conventional black plastic containers. Root-zone temperatures, particularly at the periphery of the rootball, were significantly reduced on warm days in Accelerator containers compared to those in black plastic containers. Media in Accelerator containers were slightly drier than that in black plastic containers.
Bare-root 17.5-inch-tall (44.45-cm) `Sarah's Favorite' crapemyrtle (Lagerstroemia indica L.) liners were grown in #3 [2.75-gal (10.4-L)] black plastic containers and trained to one, three, or five trunks by one of two methods. Half of the plants were established from multiple liners with each trained to form one of the trunks. The others were established by planting a single liner in each container, pruning them back to within 2 inches (5.1 cm) from the substrate surface, and then training elongating buds or adventitious shoots to the desired number of trunks. Once plants reached a marketable size they were transplanted to a landscape for two growing seasons to determine the effects of the treatments on trunk survival or growth uniformity in the landscape. The study was replicated in time with containerized `Basham's Party Pink' crapemyrtle liners, but only grown in the field for 1 year. Growth and quality differences were minimal at the end of nursery production for either clone, thus favoring recommendation of whichever treatment would be most economical to produce the desired growth form. However, in the landscape phase, survival of `Sarah's Favorite' crapemyrtle and growth and uniformity of `Basham's Party Pink' crapemyrtle were greater for several growth measures when multiple trunks were produced by training stems of the same plant as opposed to planting multiple liners. Trunk survival was generally good for three or fewer trunks, but significant losses often occurred when the planting units had five trunks, especially when grown from multiple liners. Growth and survival differences among treatments were more pronounced with increasing trunk number and the longer the planting units were in the field (landscape).
Across horticultural crops the trend is to transplant larger plants to achieve the intended landscape effects or to produce the desired yield without the long wait associated with direct seeding or small transplant technology. Consumers want immediate gratification (a landscape design that produces the desired aesthetics without the wait for plants to grow to mature sizes). This trend extends from the use of large herbaceous plants for instant landscape color, transplanting of vegetable plants already in fruit to the home garden for early yield, to transplanting larger shrubs and trees to effect the impression of an established landscape. This trend logically culminates in the transplanting of large, mature specimen trees to create the appearance of a fully mature landscape. This workshop will explore the potential benefits of this approach and the challenges associated with successful transplanting of large trees.