ARBORICULTURE ARBORICULTU & CONTENTS URBAN FORESTRY Volume 38, Issue 2, March 2012 Formerly the Journal of Arboriculture, 1975 – 2005 (Volumes 1 – 31) ® www.isa-arbor.com Adrianna Szczepaniec and Michael J. Raupp Effects of Imidacloprid on Spider Mite (Acari: Tetranychidae) Abundance and Associated Injury to Boxwood (Buxus spp.) ...................................................................................................... 37 Abstract. Boxwoods are one of the most widely used woody shrubs in managed landscapes, but they suffer frequent attack by the boxwood leafminer (Monarthropalpus flavus). The neonicotinoid insecticide imidacloprid is highly efficacious in reducing the abundance of M. flavus when applied as a foliar spray or a soil drench. Recent reports of elevated populations of spider mites following applications of imidacloprid to other species of woody plants prompted an investigation to determine the effects of imidacloprid on abundance of a specialist spider mite, Eurytetranychus buxi, and the resultant damage it causes. Boxwoods treated with imidacloprid housed significantly more E. buxi and sustained more discoloration than untreated boxwoods. Moreover, there was a direct relationship between the abundance of E. buxi and the amount of associated injury. Arborists and landscape managers should be aware of the potential for elevated abundance of spider mites on boxwoods and greater levels of discoloration following applications of imidacloprid. Key Words. Buxus spp.; Eurytetranychus buxi; Imidacloprid; Injury; Monarthropalpus flavus; Secondary Pest Outbreak. ® Joseph J. Doccola, William Hascher, John Joseph Aiken, and Peter M. Wild Treatment Strategies Using Imidacloprid in Hemlock Woolly Adelgid (Adelges tsugae Annand) Infested Eastern Hemlock (Tsuga canadensis Carrière) Trees ........................................................ 41 Abstract. Due to the widespread establishment of hemlock woolly adelgid (Adelges tsugae Annand) (HWA) across the range of eastern hemlock (Tsuga canadensis Carriere), woodland trees may be infested for many years before treatment is made. Symptoms of prolonged infestation include extensive dieback and thinned canopies. Imidacloprid, a systemic neonicotinoid insecticide, is a useful and effective tool to manage HWA. In this study, mature, large diameter trees in poor condition were treated with imidacloprid. Trees were treated once by trunk and/or soil injection in Asheville, North Carolina, U.S. Following application, changes in tree growth, HWA density and imidacloprid residues were measured for three years. Trees treated with imidacloprid recovered, whereas the untreated trees continued to struggle. Trees injected with imidacloprid accumulated compound in the canopy, facilitating refoliation and the imidacloprid persisted for three years. This extended activity of trunk-injected imidacloprid was attributed in part to slow upward movement through the restrictive tracheid vascular system and to perennial needle retention. The imidacloprid soil injection was slower to act systemically, but has potential for longer-term activity. Researchers suggest the combination of tree and soil injection for immediate and long-term (4+ years) activity as an effective and economic strategy to protect high-value trees. Key Words. Eastern Hemlock; Hemlock Woolly Adelgid; Imidacloprid, Soil Injection; Tree Injection. Evan M. Keto, Melissa R. McHale, George R. Hess, Bronson P. Bullock, and Gary B. Blank Design Choices and Urban Forest Characteristics in Raleigh, North Carolina, U.S. Parking Lots ................................................................................................................................... 50 Abstract. Trees provide important environmental, economic, and social benefits that can help to offset the negative effects of parking lots. Many cities recognize that adding space for trees in parking lots is beneficial and have created regulations that dictate minimum requirements for tree planting. However, it is not clear if tree plantings in parking lots achieve the urban tree canopy goals initially imagined by these com- munities. The study authors sampled parking lot trees in Raleigh, North Carolina, U.S., to determine how species composition and urban for- est structure vary with respect to parking lot size, shape, and design. Using a two-stage cluster sampling scheme, Raleigh’s parking lots were found to contain 44,000 ± 24,000 trees (95% confidence interval). No differences in tree compos tion were explained by the size or shape of the parking lots. Planting spaces within the parking lot that were preserved during construction were found to have more trees, canopy, and basal area per hectare than designed planting spaces in which the number, spacing, and species of trees were prescribed. Among designed planting spaces, large, linear rows had greater canopy and basal area per tree but fewer trees per hectare than smaller, circular islands. These results sug- gest that decisions made during the design process may have lasting effects on the structure and function of this portion of the urban forest. Key Words. Automobile; Car Park; Environmental Impacts; Parking Lot Design; Transportation; Tree Planting; Tree Preservation; Urban For- est Structure. ©2012 | International Society of Arboriculture | ISSN:1935-5297
March 2012
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