Treesearch

Phytophthora ramorum has become increasingly disruptive to the movement of nursery stock since it was described in 2001. Risk and mitigation assessments for P. ramorum have been done or are underway by APHIS. Because of the impact of this pathogen on forests and the nursery industry, accelerated research efforts are underway. Capturing new information in a graphic format was desirable. The lack of a single mitigation measure to effectively eliminate P. ramorum from nursery stock suggested the value of a diagram highlighting points in the disease cycle where mitigations may be effective....

In a 3-year project the elimination of Phytophthora spp. from the recirculation water with different kinds of filtration systems will be tested under commercial conditions in container nurseries. First results indicate that the filtration systems eliminate Phytophthora spp. from the water.

Potted rhododendrons grown in potting media amended with inoculum of Phytophthora ramorum became infected and showed symptoms of stem necrosis, leaf wilting, and death. P. ramorum was isolated from roots and stems of infected plants.

Phytophthora ramorum infection was modeled using the NAPPFAST system for the conterminous United States. Parameters used to model P. ramorum infection were: leaf wetness, minimum temperature, optimum temperature and maximum temperature over a specified number of accumulated days. The model was used to create maps showing the frequency of favorable years for infection and these were compared with historical P. ramorum observations from California. The majority of historical observations were located in the greater than 90 percent favorable zone using 10 year climate data. Climate risk areas...

Since 2001, the USDA Forest Service and California Polytechnic State University, San Luis Obispo have been collaborating for early detection and monitoring of the occurrence of Phytophthora ramorum, the pathogen known to cause sudden oak death (SOD). The effort consists of annual aerial surveys to map hardwood mortality in overstory tree species including coast live oak (Quercus agrifolia), tanoak (Lithocarpus densiflorus), Shreve oak (Quercus parvula var. shrevei) and California black oak (Quercus kelloggii). These aerial surveys are followed by ground surveys to locate and sample both...

Field experiments were conducted to evaluate the effectiveness of phosphonate chemical treatments for control of sudden oak death in tanoak (Lithocarpus densiflorus) and Shreve's oak (Quercus parvula var. Shrevei). Native stands of mature trees were preventatively treated with Agrifos® systemic fungicide and subsequently infected with Pytophthora ramorum. Both injection treatments as well as topical application of Agrifos® with Pentrabark® surfactant were evaluated. Experimental methods were designed to test both within tree and between tree variability. Leaves and wood samples were also...

The recent incidence of Ramorum blight, caused by Phytophthora ramorum, on many nursery crops has focused attention on improving management strategies against Phytophthora diseases in nurseries. We evaluated several chemical agents that target Oomycete pathogens for their capacity to inhibit infection of rhododendron or lilac leaves by P. ramorum (both NA strain 2027 mating type A2 and European strain D12A mating type A1) compared to other species, including P. cactorum, P. citricola, P. nicotianae, and P. citrophthora. We inoculated needle-wounded leaves from plants previously treated...

Phytophthora ramorum has been detected infecting ornamental hosts in European nurseries and gardens beginning in 1993, and detected in North American nurseries beginning in 2000. Nursery operators need a comprehensive program to insure that nursery stock remain disease free. Fungicides could be part of an integrated pest management approach to meet that goal. It is also important to evaluate whether fungicides are masking symptoms and the detection of the pathogen. For two years we evaluated fungicides for the prevention and eradication of P. ramorum on four important ornamental genera of...

The lack of knowledge regarding infection biology of Phytophthora ramorum limits our understanding of its ecology and epidemiology. Pathways of infection in Rhododendron 'Nova Zembla' were investigated using tissue culture plantlets and 3-year-old container plants inoculated with zoospore suspensions (6 x 104 zoospores mL-1) or mycelial plugs of Oregon nursery isolate 03-74-N11A. The histology of inoculated roots, stems and leaf surfaces was evaluated to identify pathways by which P. ramorum infects and colonizes plants. To observe infection, inoculated roots, stems, and leaves were...

Phytophthora ramorum is a major source of tanoak (Lithocarpus densiflorus) mortality in the tanoak/redwood (Sequoia sempervirens) forests of central California. This study presents a spatial analysis of the spread of the disease using second-order point pattern and GIS analyses. Our data set includes four plots in tanoak/redwood (Sequoia sempervirens) forests in Marin County, California. Each plot contains roughly 400 individual stems. We transformed our point pattern maps into continuous density surfaces using a gaussian kernel function for the 2001 and 2003 disease symptom surveys....