ARBORICULTURE ARBORICULTU URBAN FORESTRY Volume 32, Issue 4, July 2006 & CONTENTS ticide. Gregory A. Dahle, Harvey H. Holt, William R. Chaney, Timothy M. Whalen, Daniel L. Cassens, Rado Gazo, and Rita L. McKenzie Branch Strength Loss Implications for Silver Maple (Acer saccharinum) Converted from Round-Over to V-Trim ........................................................148 Abstract. Trees converted from round-over to V-trims could develop a canopy of potentially weak watersprouts growing on parent stems with a high probability of decay. This study was conducted to determine if the conversion from round-over to V-trimming predis- poses silver maple (Acer saccharinum L.) trees to failure, and if decay is more likely to occur in watersprouts arising aſter heading cuts than in branches arising from lateral buds. Watersprouts were mechanically pulled from converted trees and found to be 49% weaker than nor- mally occurring branches. Branch strength at failure (stress) decreased as watersprouts grew in size, and decay was present in over one-half of the watersprout at the point of failure. The conversion from round-over to V-trimming appears to predispose silver maple trees to failure. Key Words. Decay; Line Clearance; Round-Over; Silver Maple; Strength Loss; Stress; Topping; Utility Arboriculture; V-trimming; Water- sprout. Formerly the Journal of Arboriculture, 1975 – 2005 (Volumes 1 – 31) www.isa-arbor.com Ian F. Spellerberg, Nils E. Eriksson, and Vincent St. A. Crump Silver Birch (Betula pendula) Pollen and Human Health: Problems for an Exotic Tree in New Zealand ......................................................................................................133 Abstract. Silver birch (Betula pendula) is commonly used as a street tree in temperate climatic regions. However, the medical litera- ture contains a wealth of reports on the health effects of pollen from silver birch. In many countries such as New Zealand, silver birch is the main tree that causes allergic symptoms, including seasonal hayfever, asthma, and other health conditions such as food aller- gies (the oral allergy syndrome). Exposure to pollen from silver birch is more likely to occur in cities because of the numbers of the trees and the human population density. Even if there were doubts about the extent of the problem and the costs associated with the problem, the precautionary principle should apply. The healthrelated problems of silver birch should be promulgated and trees should be removed. Key Words. Allergies; Human Health Problems; Silver Birch Pollen. Jamee L. Hubbard and Daniel A. Potter Managing Calico Scale (Hemiptera: Coccidae) Infestations on Landscape Trees ............................................138 Abstract. Calico scale, Eulecanium cerasorum (Cockerell), an invasive pest of shade trees, has reached outbreak levels in landscapes and on horse farms in Kentucky, U.S. We evaluated efficacy and timing of conventional and reduced-risk foliar insecticides as well as trunk injected or soil-applied systemics for managing E. cerasorum. Acephate, bifenthrin, carbaryl, cyfluthrin, and pyriproxyfen killed young settled crawl- ers on individually sprayed shoots. Whole-canopy pyrethroid sprays, however, gave <66% control, underscoring the difficulty of reaching settled crawlers within large shade trees. Horticultural oil and insecticidal soap were relatively ineffective even with full spray coverage. Pre- ventive sprays with bifenthrin or pyriproxyfen in mid-May, at first egg hatch, intercepted crawlers before they settled on leaves. Dormant oil failed to control overwintered nymphs or reduce subsequent numbers of adults or crawlers. A plant antitranspirant applied in late March pro- vided 33% suppression. Trunk-injected imidacloprid was ineffective, whereas dicrotophos (bidrin) gave at best <50% control. Soil injection with imidacloprid in November, December, or March failed to reduce subsequent densities of adults on branches or crawlers on leaves. Rea- sons why it is difficult to eliminate calico scale in mature landscape trees are discussed in the context of the pest’s feeding sites and behavior. Key Words. Calico Scale; Eulecanium cerasorum; Integrated Pest Management; Microinjection; Plant Health Care; Scale Insects; Systemic Insec- ©2006 | International Society of Arboriculture | ISSN:1935-5297
July 2006
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