Information on emergent insect associated tree diseases including epidemiological studies of drippy blight disease of oak and thousand cankers disease of walnut
Date
2017
Authors
Sitz, Rachael A., author
Cranshaw, Whitney, advisor
Stewart, Jane, advisor
Argueso, Cris, committee member
Koski, Tony, committee member
Journal Title
Journal ISSN
Volume Title
Abstract
Two emergent disease complexes called drippy blight and thousand cankers have become injurious to hardwood trees in communities across the urban corridor of Colorado. In order to better understand these disease complexes, studies were initiated to identify the causal agents, symptomology, and epidemiology of drippy blight disease as well as determine if multiple fungi were involved in thousand cankers disease. Chapter I, published in the Journal of Arboriculture and Urban Forestry, provides information on the basic biology of drippy blight disease. This article explains the signs and symptoms of drippy blight, and shows that the bacterium Lonsdalea quercina subsp. quercina is able to cause the disease. Finally, it was noted that a kermes scale insect was abundant on all diseased oaks, but its role as a vector is unknown. Overall, this research documents the microbe and insect causal agents in this disease complex. These findings are biologically significant as the isolated bacterium was able to produce disease on several species of sapling red oaks. This, taken into consideration with other diseases caused by Lonsdalea quercina, implies that this bacterium has the potential to become widespread. Chapter II provides a detailed life history of Allokermes galliformis, the insect causal agent in drippy blight disease. Management decisions to mitigate the effects of insect damage are largely based on an understanding of the life cycle. This research documents periods when A. galliformis may be most exposed and vulnerable to controls and notes areas of the tree where it inflicts damage when feeding. Therefore, the information provided in this chapter can serve as a guide for more informed decisions when considering management of drippy blight-affected trees. Chapter III considers what insects may be involved in the dissemination of Lonsdalea quercina subsp. quercina from oaks with symptoms of drippy blight disease. Although kermes scales are the most consistent and abundant insects found in association with drippy blight disease, other more mobile insects are frequently observed on diseased trees and it was hypothesized that these may play a role in spreading the bacterial pathogen within trees and to new trees. After testing insects collected on diseased oak trees for bacterial contamination, various insects were documented to carry the bacterium, providing insight into ways the disease may move in a population of susceptible hosts. Chapter IV, published in Plant Disease, involves a tree disease characterized by an insect and fungal pathogen interaction, thousand cankers disease of walnut. This study investigates whether genetically distinct isolates of the fungal pathogen Geosmithia morbida vary in pathogenicity. Also examined was whether Fusarium solani, commonly found on diseased trees, may contribute to production of thousand cankers disease. A range of Geosmithia morbida isolates were tested alone and in combination with a Fusarium solani isolate to determine the relative contribution of each fungal pathogen to thousand cankers disease. Importantly, in Colorado Geosmithia morbida does not interact synergistically with F. solani. Overall, this research is the first to describe the emergent disease complex drippy blight and provides information to better understand the bacterial and insect causal agents. Furthermore, the investigations of drippy blight of red oak and thousand cankers disease of walnut, improve our understanding of the epidemiology of woody plant diseases that involve both arthropod and pathogen partners.