Treesearch

Studies have shown that nurseries are an important source for the spread of Phytophthora. Most surveys and studies focusing on the epidemiology of these pathogens in nurseries are based on sampling of symptomatic plants or on samples like water of different sources used for irrigation. There is little knowledge, however, on the survival and occurrence of Phytophthora in the different steps of commercial plant production. This information is necessary for the development of good management strategies for Phytophthora in nurseries. Therefore, within a 3-year project, detailed samples were...

The dominant influences on climatic patterns in the Pacific Northwest are the Pacific Ocean and the Cascade Range. The diurnal temperature range is higher east of the Cascade crest, further inland from the Pacific Ocean. More precipitation falls west of the Cascade Mountains crest, and a strong rain shadow greatly reduces precipitation east of the crest. The southern portion of the Blue Mountains, including the Strawberry subrange, is in the rain shadow of the Cascade Mountains and is predominantly influenced by Great Basin climatic patterns, resulting in warmer and drier conditions. In...

The primary purpose of this program was to demonstrate proof of concept of certain mitigation approaches at a repeat P. ramorum-positive nursery site in Washington. Approaches included steam treatment of infested soil areas; creating a gravel “sandwich” above steam-treated and potentially infested soil surfaces; improving drainage systems; required sanitation of pots, flats, and other surfaces; monitoring host plants; and training of staff to identify potential problems and symptoms associated with the life cycle of P. ramorum. Various critical control points (CCPs) were sampled for...

Soilborne inoculum (infested leaf debris which has become incorporated into the soil) may be an important contributor to the persistence of the sudden oak death pathogen Phytophthora ramorum in recurrently positive nurseries. To initiate new epidemics, soilborne inoculum must not only be able to survive over time, but also be capable of producing sporangia during times favorable to infection of plant material at the soil surface. Current research has only assessed the recovery of this pathogen after being buried in soils. Two additional aspects of the disease cycle are being investigated...

Phytophthora de Bary, a genus of Oomycetes, is known as a plant pathogenic genus. The best-known species infect a wide range of hosts, including economically valuable angiosperm and gymnosperm tree species and important agricultural crops. Many Phytophthora are invasive and have been disseminated through nursery and agricultural trade. We hypothesize that such human activities would affect the diversity of these pathogens. To test this hypothesis, we characterized and compared Phytophthora diversity between natural and urban environments in British Columbia. We collected soil samples from...

Acute Oak Decline (AOD) is a complex disease syndrome of native oak, making its first appearance in the 1980s in Britain. Since then increasing reports of its occurrence have raised concerns about cause and effects on these iconic trees. Symptomology studies confirmed that AOD is a distinctive condition with four diagnostic symptoms defining the condition; (a) weeping patches on trunks of affected trees, (b) cracks between the bark plates, (c) inner bark necrosis and sapwood degradation underlying the weeping patches, (d) over 95% co-occurrence of larval galleries of a native bark boring...

In recent years, a novel form of decline has been observed in southern and central England. This syndrome has been termed acute oak decline (AOD) and affects native oak, Quercus petraea and Q. robur. Typical symptoms include bark cracks that weep dark exudates, which are caused by necrotic patches in the inner bark. Studies show bacteria are consistently isolated from lesion edges, with two species, Gibbsiella quercinecans and Brenneria goodwinii, thought to cause tissue necrosis. Agrilus biguttatus (a native beetle, with apparently increasing populations) is often reported at affected...

Recently several national programs have been initiated calling for improving soil health and creating pollinator habitat using cover crops. Opportunities exist for nut growers to do both with the use of cover crops in our nut orchards. Because we can include perennial ground covers as cover crops, we have even more choices than landowners managing cover crops during the fallow period between agronomic crops. In addition, it's easy to see how adding some native trees and shrubs along with cover crops that we can create suitable habitats supporting bees and other pollinators.

Integrating cover crops into a nut orchard can have some unique benefits and problems not found when used cover crops during the fallow period between cash crops. Studies show ground covers can reduce hardwood tree growth anywhere from a few percent to more than 70 percent in the case of tall fescue. This means if it takes 3 years to put on one inch of diameter growth in a weed-free planting, it will take more than 9 years if growing in a tall fescue sod. Impacts on nut production appear to be even greater.

A strong focus on tree germplasm that can resist threats such as non-native insects and pathogens, or a changing climate, is fundamental for successful conservation efforts. This project is predicated on the fact that genetic resistance is the cornerstone for protecting plants against pathogens and insects in environments conducive to the attacking organisms, a principle we have extensively applied to the study of coast live oak (CLO – Quercus agrifolia) interactions with Phytophthora ramorum in California wildlands. The largest obstacle to the implementation of host resistance as a tree...