ARBORICULTURE ARBORICULTU & CONTENTS URBAN FORESTRY Volume 43, Issue 6, November 2017 Formerly the Journal of Arboriculture, 1975 – 2005 (Volumes 1 – 31) ® www.isa-arbor.com Fredric Miller and Donna Danielson Relative Susceptibility Among Arborvitae Cultivars to Arborvitae Leafminer, Argyresthia thuiella (Lepidoptera: Argyresthiidae). .......................................................................................205 Abstract. Eighteen Thuja species and cultivars were evaluated for ovipositional preference for, and relative susceptibility to, feeding by the arborvitae leafminer. Thuja occidentalis ‘Hetz Midget’ and ‘Hoopesii’ were least susceptible; T. occidentalis cultivars 'Gracilis', 'Holmstrup', 'Spiralis', and 'Techny', and T. plicata 'Fastigiata', were intermediate in susceptibility; Thuja occidentalis cultivars 'Aurea', 'Douglasii Aurea', 'Globosa', 'Hetz Wintergreen', 'Smaragd', 'Umbraculifera', 'Wagneri', 'Wareana,' and 'Waxen', and species T. occidentalis, and T. plicata, were highly susceptible to ALM feeding. Short trees suffered significantly less feeding compared to tall trees, with number of infested branch tips (IBTs) increasing with tree height. Short trees (<4 m) had significantly more feeding damage in the upper canopy zone and tall trees (>4 m) had greater damage in the lower and middle zones. Trees with very dense canopies had significantly fewer IBTs compared to trees with sparse, medium, and dense canopies, with IBTs decreasing as canopy density increased. There were no significant associations between num- ber of IBTs and canopy aspect. Plant height, growth habit, and canopy zone and density appear to influence infestation levels and possi- bly ovipositional preference. These findings suggest some important ALM management guidelines for the nursery and landscape industries. Key Words. Arborvitae; Arborvitae Leafminer; Argyresthia thuiella; Insect Ovipositional Preference; Susceptibility; Thuja. Michael Marcotrigiano Elms Revisited ...........................................................................................................................217 Abstract. Until Dutch elm disease (DED) was accidentally introduced into the United States around 1930, the streets in many states were lined with American elms (Ulmus americana). This review highlights the aftermath of DED, and updates read- ers on the advances in our knowledge of the pathosystem, which consists of a tree, a fungal pathogen, and an insect vector. Conven- tional breeding has produced new cultivars of American elm that are more disease-tolerant, although still not resistant. Suitable DED-resistant hybrid elms have been bred using species from Europe and Asia. The discovery of diploid populations of American elm may open new opportunities in elm hybridization and genome analysis. Growing knowledge of resistance mechanisms reveals a complex interaction of anatomy, physiology, environmental factors, and tree age. The beetle’s role is largely understood but appears not to be a viable point of attack in the war on DED. The genome of the fungal pathogen has been sequenced, and gene expression studies are well under way. There is a renewed interest in understanding the evolution, genetics, and physiology of the DED pathogen. The genetic engineering of elms has been demonstrated but not with the specificity and vigor as has been reported for genetically engineered American chestnut. Elm yellows, caused by a phytoplasma, are still a deadly problem for elms, although outbreaks are more regional than for DED. Germplasm resources are critical to elm improvement, and the first comprehensive survey of living elm species, hybrids, and cultivars growing in America is presented in tabular form. Key Words: American Elm; Dutch Elm Disease; Elm; Elm Bark Beetle; Elm Yellows; Germplasm Storage; Ophiostoma novo-ulmi; Transgenic Tree; Tree Breeding; Ulmus. ©2017 | International Society of Arboriculture | ISSN:1935-5297
November 2017
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