Treesearch

Since 2005, we have been studying the spread and development of Phytophthora ramorum at a Christmas tree farm near Los Gatos, California. This research has shown that distance from infected plants, predominantly California bay laurel (Umbellularia californica) (referred to as ?bay? throughout), is an important factor relating to the infection of Douglas-fir (Pseudotsuga menziesii) and grand fir (Abies grandis) Christmas trees at our research site. This abstract reports two case studies involving the possible role that bay inflorescences and mistletoe may play in the spread of P. ramorum.

The invasive Phytophthora ramorum, P. kernoviae, and other aerial Phytophthoras are causing bleeding lesions on the trunks of mature trees, especially beech (Fagus sylvatica), in Cornwall, southwest England. The relationship between the results of host susceptibility tests using wound inoculation of excised logs in the laboratory and field observations in Cornwall has generally been good. However there have been some discrepancies. For example European sycamore (Acer pseudoplatanus) is moderately to highly susceptible to Phytophthora ramorum and P. kernoviae in the lab tests but is rarely...

Increasing numbers of studies are finding that humans can facilitate the spread of exotic plant species in protected wildlands. Hiking trails commonly serve as conduits for invaders and the number of exotic plant species occurring in protected areas is often correlated positively with visitation rates. Despite such evidence linking human activity to the spread of exotic plants, few studies have addressed this possibility for plant pathogens.

Sudden oak death, caused by the water mold Phytophthora ramorum, is a plant disease responsible for the death of hundreds of thousands of oak and tanoak trees. Some foliar hosts play a major role in the epidemiology of this disease. Upon infection by P. ramorum, these foliar hosts express non-fatal leaf lesions from which large amounts of inoculum can be produced and spread to neighboring host individuals, including oak species. Umbellularia californica (California bay laurel) may be one of the most important foliar hosts of sudden oak death due its observed ability to produce inoculum and...

Soil samples were collected from quadrats marked out below the canopies of two rhododendrons, one infected by Phytophthora ramorum (Site 1) and the other (Site 2) infected by Phytophthora kernoviae and P. ramorum. Rainwater was collected in high-level and low level traps. Soil and rainwater were sampled at roughly monthly intervals from November 2003 until April 2006, and tested for the presence of P. ramorum and P. kernoviae at the Central Science Laboratory. The infected rhododendrons were removed in May 2004 (Site 1) and July 2004 (Site 2) after which the quadrats and rain traps were...

Phytophthora ramorum is a plant pathogen introduced into Europe and North America. It can infect any host species belonging to different botanical families within the seed plants. Such infective capacity indicates that it can overcome basic plant defence responses that have been phylogenetically conserved in plants (Heath 1991). In addition, P. ramorum is capable of infecting woody plants that are not predisposed (i.e. physiologically healthy) and can colonize a diversity of ecological niches such as leaves, stems, trunks and maybe roots and fruits. All these traits make P. ramorum...

The risk of conifers being infected by Phytophthora ramorum under natural conditions is poorly understood. In California, infected conifers commonly occur as understory plants beneath or adjacent to heavily infected plants like California bay laurel (Umbellularia californica). During wet periods, P. ramorum is known to produce a copious amount of spores from spots on infected leaves of this epidemiologically-important host. In Oregon, infection on California bay laurel is limited and infection of Douglas-fir (Pseudotsuga menziesii) trees has been limited to a few seedlings directly beneath...

For over three decades, geologists, hydrologists and stream ecologists have shown significant interest in suspended load in running waters. Physical scientists have focused on turbidity, the development of sediment-rating curves and estimation of sediment yields, often as an indicator of changing land uses (Beschta 1981). Stream ecologists, on the other hand, have focused on 1) the role of suspended sediments in water quality degradation and its deleterious impacts on biological communities (for example, Waters 1995); or 2) its beneficial roles in providing food resources for filter-feeding...