Scientific Research Journal Update

Susan Switras and Jeff Gillman

The recent months have brought a wide variety of nursery-related articles, focusing on such issues as cold hardiness, pest control, container production and even wastewater reclamation. Propagation and growth regulation were also subjects of published study. Several articles have been summarized here, and each is followed by a full citation. We recommend looking up these articles for yourself if you have any questions regarding the research. Some of these studies were conducted in places with different conditions than Minnesota.

We are reporting the results of other peoples' research and neither endorse nor refute the methods which they use or the results which they report. In many of these articles information regarding a particular compound or pesticide is given which does not necessarily follow label recommendations. We strongly discourage the use of these compounds and pesticides in a way that is inconsistent with the label.

·        The connection between specimen age and cold hardiness was the subject of a study out of the Minnesota Landscape Arboretum in Chanhassen. Steve McNamara and Harold Pellett evaluated the cold hardiness of seedling and mature Sakhalin corktree (Phellodendron sachalinense Friedr. Schmidt) during their fall acclimation period. Seedlings aged 10-, 22-, and 34- months were hardy to -4EC (24EF) on October 9 while their 35-year-old parent was hardy to -12EC (10EF). Seventeen days later, the parent and 34-month-old plants were hardy to -16EC (3EF). In January, the 10- and 22-month-old seedlings had died back to the snowline while the other plants showed no winter injury. The seedlings attained comparable hardiness to the adults after their fourth season of growth. (1)

·        Another study concerned with cold injury came out of Kansas State University. Alice De Luc, Linda Parsons and John Pair looked at the connection between winter severity, landscape exposure and survival and growth of three boxwood cultivars: 'Winter Gem' (Buxus microphylla Sieb. & Zucc.) and 'Green Velvet' and 'Green Mountain' [B. sinica (Rehd. & Wils.) Cheng var. insularis (Nakai) M. Cheng H B. sempervirens L. 'Suffruticosa' L.]. Plant performance for all cultivars was better at the northern exposures (N, NNE, ENE, NNW, WNW) than at the southern exposures, regardless of USDA hardiness zone. At the colder site, 'Green Mountain' and 'Green Velvet' performed better at the southern exposures than 'Winter Gem.' Lows during this experiment were -25EC with 24-hour temperature drops of 31-32EC. (2)

  • To address the problem of irrigation sources during drought periods, R. Gori et al. out of the University of Florence in Italy evaluated the response of Abutilon 'Kentish Belle,' Weigelia florida 'Bouquet Rose' and Viburnum tinus 'French White' to irrigation with reclaimed wastewater (RW). They found that the wastewater was a source of low levels of nitrogen, phosphorus and potassium. The salinity, conductivity and calcium content was also higher in RW than well water. After 23 weeks of irrigation, the viburnum and weigelia showed increased shoot growth in plants watered with RW over plants watered with RW over plants watered with well water. The RW increased the shoot/root ratios and leaf area was also increased. RW-treated plants also showed increased foliar nitrogen and potassium and decreased foliar iron. (3)

  • Ursula Schuch, Dennis Pittenger and Phillip Barker of the University of California Riverside published a study on container effects on root systems and subsequent field performance of two nursery species. Brazilian Pepper tree (Schinus terebinthifolius Raddi.), a coarse-rooted species, did not perform well in tall, narrow containers, so biomass production was lowered during nursery and field establishment. The ficus (Ficus retusa L. 'Nitida'), with its fibrous root system was unaffected by container shape and size. During the nursery phase, rootball quality of both species was improved by cupric hydroxide (as Spinout) applied to the inner surface of the container. (4) While neither of these species are hardy in our area, these results may have implications on other species with the same root type.

  •  Seaside alder (Alnus maritima [Marsh.] Nutt.) is a rare North American species that has garnered recent interest as a new nursery crop. James Schrader and William Graves at Iowa State University evaluated the use of softwood cuttings in seaside alder propagation. Cuttings from Oklahoma performed better than cuttings from the Delmarva Peninsula across IBA treatments. Cuttings rooted best when collected early in the season and treated with 8 g/kg-1 IBA. (5)

  • Scagel and Linderman, at the USDA-ARS Horticultural Crops Research Laboratory in Oregon, looked at the effect of root treatment with plant growth regulators (Hormogel, Stimroot, ethrel alginate) on bareroot conifers. Stimroot and Hormogel increased the height growth in western larch (Larix occidentalis Nutt.), Douglas-fir [Pseudotsuga menzesii (mirb.) Franco.], and lodgepole pine (Pinus contorta Dougl.) while ethrel increased the height of Englemann spruce (Picea englemanii Parry). Larch stem diameter was increased by all treatments, lodgepole pine diameter was not increased by any treatment, and Stimroot increased stem diameter in the other two species. All treatments increased IAA content in the roots of western larch, Englemann spruce and Douglas-fir. IAA content in lodgepole pine was only increased by treatments containing IBA. (6)  IAA and IBA are auxins, which stimulate root growth.

1. 1.McNamara, S. and H. Pellett. 2000. Cold hardiness of Phellodendron sachalinense Friedr. Schmidt seedlings increases with age. HortScience 35(2):304-305.

2. 2.Le Duc, A., L. R. Parsons and J. C. Pair. 2000. Growth, survival, and aesthetic quality of boxwood cultivars as affected by landscape exposure. HortScience 35(2):205-208.

3. 3.Gori, R., F. Ferrini, F. R. Nicese and C. Lubello. 2000. Effect of reclaimed wastewater on the gorwth and nutrient content of three landscape shrubs. Journal of Environmental Horticulture 18(2):108-114.

4. 4.Schuch, U. K., D. R. Pittenger and P.A. Barker. 2000. Comparing effects of container treatments on nursery production and field establishment of trees with different root systems. Journal of Environmental Horticulture 18(2):83-88.

5.

5.Schrader, J. A. and W. R. Graves. 2000. Propagation of Alnus maritima from softwood cuttings. HortScience 35(2):293-295.

6. 6.Scagel, C. F. and R. G. Linderman. 2000. Changes in root IAA content and growth of bareroot conifers treated with plant growth regulating substances at planting. Journal of Environmental Horticulture 18(2):99-107.