Select a title from the list below to see an abstract of the article. For information about ordering reprints of complete articles, contact ISA at (217) 355-9411 or isa@isa-arbor.com.
Abstract. Several fungicides and chemical combinations were sprayed on southern magnolia trees to improve leaf condition and tree appearance. Leaf spot and leaf scorch symptoms, induced by the fungus Glomerella cingulata, were reduced significantly by sprays with benomyl, chlorothalonil, propiconazole, myclobutanil, or copper hydroxide. Addition of a non-ionic surfactant in sprays resulted in phytotoxicity, visible as a ring spot or faded brown patch on leaves. Tank mixing of copper hydroxide with other fungicides also increased phytotoxicity and did not improve disease control or leaf condition. Benomyl and propiconazole treatments were among the best in improving overall tree appearance.
Abstract. Tree wounds are often accompanied by the dieback of uninjured cambium at the edges of the wound. Dieback increases wound size and lengthens the time that xylem is exposed and susceptible to colonization by decay fungi. Wrapping new wounds with polyethylene plastic sheeting (PEP) can reduce dieback and promote the formation of callus tissue. Fresh wounds on aspen and maple wrapped with PEP had significantly less dieback than unwrapped wounds after 14 weeks. When PEP treatment was delayed 1 week or longer after wounding, there was no difference in wound size. Fresh wounds of aspen wrapped with PEP for 1 week were significantly smaller than unwrapped wounds after 15 weeks. In maple, 2 weeks of wrapping with PEP was required to improve wound closure. The use of PEP on wounds of birch did not affect wound size. Wounds of aspen continuously wrapped for 2 years with PEP did not have more colonization by decay fungi than untreated control wounds.
Abstract. Paclobutrazol 2SC (PBZ) was injected into the soil at the base of the trunk at 2 g a.i. per inch dbh. Surface fine root densities near the base of the trees were naturally higher than in the rest of the root system and were adequate to absorb the compound. PBZ treatment was effective in stimulating fine root development in pin oaks (Quercus palustris) and white oaks (Quercus alba). Pin oak fine root densities were increased significantly in high-quality topsoil. White oak fine root densities were increased significantly by PBZ alone and in combination with high-organic replacement soils. The treatment may be effective in stabilizing declining trees with insufficient fine root development.
Abstract. Forty flowering dogwood trees were subjected to 1 of 5 defoliation levels (0% , 25%, 50%, 75%, and 100% defoliation). Defoliation impact was assessed by measuring changes in diameter, twig extension growth, and electrical resistance of the cambium. Electrical resistance in the cambium increased for plants that were totally defoliated. Circumference growth of flowering dogwood was reduced 50% by total defoliation when compared to defoliated plants. Twig extension growth of defoliation stressed trees was reduced á35% as defoliation levels reached 75% and 100%. Both increases in circumference and twig extension growth are affected by defoliation stress. Twig extension growth is the best measure of defoliation stress because it has the advantage of not requiring wounding when used to assess the impact of defoliation stress after the fact.
Abstract. Canada's national tree planting program, Tree Plan Canada, recently underwent a major change. In 1995, funding ended for tree planting projects by small groups and local organizations. This paper summarizes the Northwest Region's planting of 8.5 million trees in 347 projects. After 1 to 3 years, 74% of the trees per project were in healthy condition. The program involved 93,000 people directly in new tree planting activities. The maximum potential for sequestering carbon with this program was estimated to be 4000 tonnes per year.
Abstract. Experiments were designed to determine how moisture content of aspen trees is related to infection and expansion of Cytospora cankers, whether Cytospora chrysosperma propagules are found on or in aspen bark, and if there is variation in virulence among C. chrysosperma isolates. Cankers were significantly larger on drought-stressed trees than on nonstressed trees. In the spring, wounds on drought-stressed, potted aspen trees, Populus tremuloides, were susceptible to infection by C. chrysosperma for at least 10 days after wounding. Wounds on nonstressed trees were susceptible for about 4 days. Resistance to canker initiation, as measured by the number of expanding cankers, was expressed about 7 days after wounding on stressed trees. Resistance in nonstressed trees was observed within 2 days. Cytospora was not found on asymptomatic trees as an inner bark inhabitant but was found on bark surfaces. Virulence of C. chrysosperma isolates was significantly different among isolates from 8 different hosts and 5 isolates from aspen when inoculated on aspen.
Abstract. Computer models have shown that proper placement of trees around climate- controlled buildings can significantly contribute to energy conservation by lowering cooling requirements in summer months and heating requirements in the winter. A study conducted in a residential neighborhood of Ann Arbor, Michigan, uses electric and natural gas utility company records to examine energy demand for homes in 3 areas with distinctly different levels of tree stocking. Field measurements quantify the density of vegetation that casts shade directly on homes, and aerial photo interpretation is used to evaluate potential wind shielding offered to individual homes by vegetation and adjacent buildings. Statistical analysis of data indicates that variability of structures, including different levels of insulation, infiltration, and efficiencies of space-conditioning appliances mask the effects of vegetation on energy use. Analysis is further complicated by a wide range of energy use habits of individual homeowners. However, trends are observed that suggest proper placement of trees with regard to seasonal solar gain and wind patterns may yield substantial savings of energy. Improper placement of trees may yield a significant increase in net levels of energy used for space conditioning.
Abstract. One-gram a.i. flurprimidol tablets (Cutless Tree Implant) were inserted into the trunks of golden shower trees (Cassia fistula) on August 8, 1993. Plants were topped in June 1994 and again in December 1994. Regrowth after each topping was measured. There was no consistent influence of flurprimidol on growth of C. fistula. Paclobutrazol (Profile ) applied as a basal drench reduced growth of Queen palm (Syagras romanzoffiana) and Manila palm (Veitchia merrillii) 11 months after application.