Published by the International Society of Arboriculture.
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.
By D.W. Burger, G.W. Forister, and R. Gross
Abstract. Short-term (aerated solution culture and container nursery) and long-term (landscape) experiments were conducted to study the effect of treeshelters on the root and shoot growth of several ornamental trees (Sequoia sempervirens (D. Don) Endl., Quercus lobata Née, Quercus agrifolia Née, Lagerstroemia indica L. 'Watermelon Red', Ginkgo biloba L., Platanus racemosa Nutt., Fraxinus latifolia Benth. and Populus euamericana cv. Giacometti). In general, plants grown in treeshelters were taller and some had reduced caliper growth. Treeshelters reduced top dry mass of F. latifolia, P. racemosa, Q. agrifolia, Q. lobata and P. euamericana and also reduced root dry mass, root:shoot ratio, total root length and total root area for all species/cultivars except Q. agrifolia. The results are explained on the basis of the microenvironment in/around treeshelters, photosynthetic partitioning and immobilization of plants growing in shelters. Management challenges and potential usefulness of treeshelters in landscape transplanting are also discussed.
By David W. Onstad, David J. Nowak, and Michael R. Jeffords
Abstract. The gypsy moth, Lymantria dispar, will soon become established in much of the Midwest. If an outbreak with extremely high population levels of this serious defoliator is allowed to occur in the Chicago area, what kind of damage can be expected? A model for defoliation, refoliation and mortality was developed based on the number of trees and associated leaf biomass for each tree species classified according to its attractiveness to or probability of infestation by gypsy moth. Data for eight land uses in the Chicago metropolitan area were used in the model. Vacant lands, institutional lands dominated by vegetation (e.g., parks, cemeteries, golf courses), and residential areas have the highest tree densities and other characteristics that make them valuable as well as vulnerable to gypsy moth infestation. The highest percentage of most-preferred tree species and highest percent defoliation is predicted to occur on vacant lands, followed by institutional lands dominated by vegetation, and residential areas. The potential defoliation by gypsy moth in the Chicago area is relatively modest, ranging from 14% in Chicago and suburban Cook County to 26% in DuPage County. Localized defoliation can be higher, however, particularly on institutional lands dominated by vegetation and vacant lands, where defoliation estimates range between 23 and 40%. Less than one- tenth of one percent of the total number of trees in the entire Chicago area are predicted to die because of gypsy moth defoliation during an outbreak.
By Karen Jetter, Dr. Karen Klonsky, and Dr. Charles H. Pickett.
Abstract. The ash whitefly (Siphoninus phillyreae) was first identified in California during 1988 and caused widespread defoliation to its primary hosts, ash (Fraxinus species) and ornamental pear (Pyrus species) trees. The ash whitefly caused higher levels of damage to trees in regions with hotter summers and lower damage to trees in regions with cooler summers. In 1990 a parasitic wasp, Encarsia inaron (=partenopea), was released into urban communities in California to control the ash whitefly infestation. By 1992 the wasp had reduced ash whitefly populations to undetectable levels and preserved the aesthetic benefits of the affected trees. The loss in aesthetic benefits due to ash whitefly damage was estimated using a standard tree appraisal technique, the Trunk Formula Method. The benefits were estimated as the change in the average appraised value of a susceptible tree due to ash whitefly damage times the number of each affected tree species for each region. The total benefits of the biological control program range from $324 million at wholesale values to $412 million at retail. The direct costs of the program were just over $1.2 million. The net benefits are between $323 million and $411 million. The respective benefit to cost ratios are $270:1 and $344:1.
By Janelle W. Johnson, Mark L. Gleason, Sharon K. Parker, Ellen B. Provin, Jeffery K. Iles, and Paula H. Flynn.
Abstract. Saplings of Pinus sylvestris were subjected to drought stress periods and inoculated with Sphaeropsis sapinea in a greenhouse experiment. Six wk after inoculation, saplings that had low needle water potentials for 14 to 21 days after inoculation exhibited more dieback and developed significantly (P < 0.05) longer cankers than saplings that had equivalent water stress for 3 to 4 days after inoculation or unstressed saplings. The results indicate that drought stress increases susceptibility of Scots pine to Sphaeropsis canker and that canker growth can be suppressed by watering drought-stressed trees.
By Mark L. Gleason, Sharon K. Parker, Tiffany E. Engle, Paula H. Flynn, Helen M. Griffiths, Mark A. Vitosh, and Jeffery K. Iles
Abstract. Green ash in nine cities in Iowa and Wisconsin were surveyed in August and September 1994 for occurrence and impact of ash yellows (AshY) phytoplasma infection. In each city, the survey included 12 arbitrarily selected trees in each of three crown condition categories: less than 10% crown dieback, 11 to 30% crown dieback, and more than 30% crown dieback. Up to four trees per community with witches'-brooms were also sampled. Occurrence of phytoplasmal infection in sampled trees lacking witches'- brooms ranged from 3% to 19% among the cities in the survey. The number of trees that tested positive for phytoplasmas, or that exhibited epicormic sprouts, deliquescent branching, basal bark cracks, or basal shoots, did not differ significantly among the crown dieback classes sampled. Trees that displayed witches'-brooms or basal shoots were significantly (P<0.005) more likely to be infected with phytoplasmas (54%) than trees lacking these symptoms (13%). The presence of epicormic sprouts, deliquescent branching, or basal bark cracks was not significantly associated with presence of phytoplasmas. Trees infected with phytoplasmas had significantly (P<0.0001) less radial growth than noninfected trees from 1973 to 1994.
By John Houde
Abstract. Preservation of trees on public property is becoming an important issue with demolition of existing houses and the construction of new homes on existing house lots. In the Chicago area, Glencoe, Highland Park, Park Ridge, Winnetka and others have experienced this redevelopment process. Glencoe as a case study offers us an insight into steps that can be taken to preserve established parkway trees from construction damage. This article describes how to structure the bureaucracy of municipal government to successfully preserve street trees in older established towns or neighborhoods.
By Tom Dierauf, Joel Artman, John R. Elkins, S. Lucille Griffin, and Gary J. Griffin
Abstract. The American chestnut [Castanea dentata (Marsh.) Bork.] was greatly valued as a landscape and forest tree in the eastern United States until the chestnut blight fungus [Cryphonectria parasitica (Murr.) Barr] killed all but a few trees during the first half of this century. Some of the large American chestnuts that survived the blight epidemic have been found to have low levels of blight resistance (2). These trees typically have had several to many limbs killed by blight. Most of these surviving trees were found to be infected by virulent (killing) strains of the blight fungus and also by strains of the chestnut blight fungus that had low virulence (hypovirulence) (2). Biological control of chestnut blight with hypovirulence has potential (3). In general, however, a high level and long-term control of chestnut blight using hyporvirulence (inoculation of cankers with hypovirulent strains) has not been successful in the eastern United States. The present investigation was undertaken to document a high level of chestnut blight control on grafted American chestnut trees, derived from large survivors, which had been inoculated with hypovirulent strains 13-14 years earlier.