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Pitch canker was first recognized in California in 1986 affecting Monterey pines (Pinus radiata) near Santa Cruz. The causal agent, Fusarium circinatum, had previously beendescribed from infected pines in the southeastern U.S. Thousands of trees have been killed in both native and urban forests throughout coastal California, suggesting that this fungus is a new invasive species. Since the late 1980s, David Wood (ESPM), Tom Gordon (UCD) and I have worked on a multidisciplinary project focusing on mechanisms of spread, host responses, impacts, and management options. An extension program has been developed with Rick Standiford (ESPM). (See http://nature.berkeley.edu/forestry/curr_proj/pitch/pitch.html) In the southeastern US, infection by pitch canker occurs through wounds. In Cali-fornia, however, the pathogen is vectored into host trees by insects, parti-cularly bark beetles, which utilize dead, diseased and dying host mate-rial. A model has been developed that estimates the proportion of bark beetles in a population that are present due to the disease as opposed to those that are present carrying out their natural roles. All native California pines tested are susceptible to the pathogen. In addition, the pathogen has some affect on Douglas-fir and some exotic pines. The susceptibility of Monterey pine ranges from resistant to very susceptible. Repeated exposure to the pathogen results, at least in the short term, in an increase in resistance to subsequent exposure (systemic induced resistance). An integrated pest management program aimed at mitigating the impacts of the disease has been developed. As with most tree diseases, there is no cure. Approaches to management include selecting appropriate tree species, utilizing resistant varieties of susceptible species, and managing diseased trees such that systemic induced resistance may be expressed. Recommendations to reduce the spread of the pathogen may in-clude disposing of diseased material by chipping and composting, and restricting the movement of nursery stock, seeds, chipped material, and unprocessed logs.
In 1995 there were reports about mortality of tanoak in Marin County near Mt. Tamalpais. Symptoms included rapid browning of trees, bleeding stem cankers, and high levels of oak bark beetle and ambrosia beetle. Similar mortality was reported near Santa Cruz and Big Sur. By 1998 similar symptoms were observed on coast live oak and California black oak by UC Cooperative Extension Farm Advisors Pavel Svihra (Marin and Sonoma Counties) and Steve Tjosvold (Santa Cruz and Monterey Counties). In 1999 a multidisciplinary research team of UC scientists was formed to address the cause and management options for control of "Sudden Oak Death". A 23-person team was formed including forest pathologists, forest entomologists, ecologists, silviculturists, wildlife biologists, remote sensing/GIS experts, and urban forestry/arboriculture experts from UC Davis and UC Berkeley, and advisors from CE county offices. Funds were provided by both UC and the USDA Forest Service. Objectives were to identify possible causal agents, determine the extent of mortality, and monitor symptom develop-ment. By the fall of 2000, the state's Forest Pest Council established a multi-agency and organization task force California Oak Mortality Task Force (COMTF). UC Davis plant pathologist Dave Rizzo was able to culture a previously unknown species of Phytophthora, which seemed to be the source of mortality. UC Berkeley CE Special-ist in forest pathology Matteo Garbelotto's genetic investigations suggested that the mortality-causing organism was not one of the 60 previously known species of Phytoph-thora. National and international experts, working closely with members of the UC research team, found the same organism in Rhododendrons in Europe and in Santa Cruz County. UC Berkeley CE Natural Resource Monitoring Specialist Maggi Kelly developed a web-based monitoring effort that has systematically mapped the distribution of dying trees. For details see:
The red gum lerp psyllid (Glycaspsis brimblecombei) was first detected in June 1998, in LA County, and infestations were observed elsewhere in California a month later. The insect feeds on several Eucalyptus species, but prefers river red gum (E. camaldulensis). The psyllid constructs a white, conical cover of sugar, called a lerp, under which it feeds. Infested leaves become covered with lerps, which are often covered with sticky honeydew and black sooty molds. The psyllid popu-lations can reach very high densities and cause extensive defoliation and even death. We began our biological control program in February of 1999 by setting up 10 sticky traps at each of two sites. By June 2000, we had 26 monitoring sites statewide. With many cooperators we change 326 traps weekly and count and sex adult psyllids and monitor adult parasitoids. We also sample foliage every three weeks at two locations in LA and another in Alameda Co. There is an excellent relationship between the number of adult females caught in the sticky traps and the immature stages on the foliage samples, particularly eggs. In August 1999, eight species of lerp psyllid parasitoids were collected at several locations in southern Australia. One species which did well in our rearings, Psyllaephagus bliteus, was selected and a series of host specificity tests were conducted with three other psyllid species, including a melaleuca psyllid which is a candidate for the biological control of melaleuca in the Florida Everglades. P. bliteus appears to be specific to the red gum lerp psyllid so we started a mass rearing program. The first parasitoid release (about 50 females) was made in June 2000, in North Hollywood. Since then we have made releases in 17 other locations throughout the state. The first field recovery of a parasitoid was made two months later on a sticky trap in San Mateo County 10 miles from where the parasitoids were released. In October, 2000, we recovered parasitized lerps from foliage at the LA site, four months after parasitoid release. It appears that we have established populations of the natural enemies of the lerp psyllid but, because of the small numbers released, we don't expect immediately detectable effects on psyllid populations. The monitoring of psyllids and parasitic wasps will continue for the next two years. |
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