Treesearch

Sudden Oak Death (SOD) is the common name for a disease caused by Phytophthora ramorum (oomycetes), an invasive plant pathogen of regulatory concern. The nursery, timber, forest specialty product, and Christmas tree industries in Washington are at risk because of the spread of P. ramorum within nurseries and from nurseries into waterways and the landscape. This study was initiated in 2010 in order to monitor for early detection of P. ramorum in western Washington streams and ponds. Since P. ramorum, to date, has been documented to be established in only a few WA streams, this survey...

The spread of Phytophthora ramorum from infested areas in nurseries and landscape sites is commonly associated with the movement of inoculum in water or from the movement of contaminated soils. It has been shown that P. ramorum can survive asymptomatically on roots of containerized plants and in potting media. The development and implementation of cost effective and environmentally acceptable best management practices (BMPs) to limit the spread of P. ramorum has been identified as a high priority need by the nursery and forestry industries as well as state and federal regulatory agencies.

Phytophthora ramorum continues to cause extensive mortality of tanoaks in southwestern Oregon. Effective management strategies have been developed based on our current understanding of the pathogen’s epidemiology. Local dispersal can occur either by canopy throughfall (“top-down”) or a ground splash (“bottom-up”) pathway. Although the “top-down” aspect of the disease cycle is well understood, the importance of infested soil and leaf litter as contributing factors to the spread of disease remains unclear. To elucidate the epidemiological importance of these “bottom-up” sources of inoculum,...

For more than a decade, the Rizzo lab and collaborators have monitored northern and central coastal California watersheds each spring and early summer for the presence of Phytophthora using submerged Rhododendron leaves as bait. This served as an early detection tool for the sudden oak death (SOD) pathogen, P. ramorum, but other species of Phytophthora were encountered and notable isolates occasionally saved; in recent years a more concerted effort was made to isolate species of Phytophthora other than ramorum. Twenty-three species were identified using a combination of morphological...

The Santa Clara Valley Water District (District) is a wholesale water supplier for 1.8 million people in Santa Clara County, California. Capital, water utility, and stream maintenance projects result in extensive, long-term mitigation requirements in riparian, wetland, and upland habitats throughout the county. In 2014, several restoration sites on the valley floor and in the upper watershed were found to be contaminated by Phytophthora spp. Subsequently, an extensive baseline study of restoration sites planted in the last 3 years revealed 31 different species of Phytophthora in 16 sites,...

In partnership with the California Native Nursery Network, the three agencies of the Golden Gate National Parks (National Park Service, Golden Gate National Parks Conservancy, and Presidio Trust) hosted the Symposium, “Responding to an Expanding Threat: Exotic Phytophthora Species in Native Plant Nurseries, Restoration Plantings, and Wildlands” in December of 2014. The symposium was intended to educate and inform the regional restoration and native plant nursery communities on recent findings and concerns of Phytophthora species that are being discovered in native plant nurseries and...

The prevalence of Phytophthora species in surface waters has earned increasing attention in the past decades, in great part as a result of “stream monitoring” programs for detection and monitoring of Phytophthora ramorum and other invasive species. The potential for Phytophthora to survive and reproduce in streams has significant implications for evaluating and managing the risk of spread of pathogenic species. Therefore, it is important to understand the ecology of both introduced and endemic species in aquatic environments. Leaf litter is a potential substrate for the persistence and...

Soilborne Phytophthora spp. can be important for initiating disease through movement of inoculum with surface water to roots or splashing onto foliage. Nursery beds infested with Phytophthora spp. can contaminate container plants set on them, causing disease year after year and posing a risk of additional spread. Persistent sources of soilborne inoculum are especially problematic for quarantine pathogens such as P. ramorum. Unfortunately, infested nursery beds are challenging to disinfest because of restrictions on the use of soil fumigants and the difficulty of accessing equipment for...

In 2012, Phytophthora tentaculata was detected for the first time in North America on the roots and crowns of declining sticky monkey flower plants (Diplacus aurantiacus) in a Monterey County, CA native plant nursery. At the time, P. tentaculata was listed among the top five exotic Phytophthora species of concern to the US due to its potential economic and environmental impacts. In 2014, P. tentaculata was detected on toyon (Heteromeles arbutifolia) and again on sticky monkey flower plants that had been outplanted at a restoration site in CA. These plants originated from a different CA...

A survey of areas previously anthropogenically disturbed and revegetated with woody nursery-reared native Californian vegetation was conducted in Santa Clara County between August and December of Previous sampling of revegetation sites had found nursery-origin transplants to be infested withPhytophthora species. Samples of roots and soil were collected from underneath dead, symptomatic, and non-symptomatic transplants at 24 sites and baited with a combination of pear fruit and Rhododendron leaves. Strains were isolated in 18 (75%) of the sites surveyed and 55 of the 145 samples baited,...