Figure 16 — Known locations of annosus root disease in California.
California black oak. Septoria leaf blight defoliated black oaks in many places. Damage at only one location caused crown dieback in 1994 and 1995 (see section M261A).
Douglas-fir. Two defoliators have recently been reported on Douglas-firs. One of the defoliators, a newly named walkingstick, Timema douglasi, has defoliated Douglas-firs in several locations and, in at least one instance, has caused tree mortality. The second defoliator is citrus thrips or a close relative. This insect causes a curling of the needles of Douglas-firs and reduces their value as Christmas trees. Insecticidal controls are being tested; at this time, results are inconclusive.
Damage from both of these insects appears to be decreasing, but the long-term effects their presence may have on forest health over larger areas is not known. Whether these insects on Douglas-fir are new or their damage has just recently been recognized is also not known.
Monterey pine. Pine pitch canker was identified in landscape plantings of Monterey pine near Santa Rosa and Ukiah. These cities are the northernmost known extension of the disease. Damage has not increased and appears to have stabilized. The fungus has not spread beyond these locations.
Port-Orford-cedar. Port-Orford-cedar root disease was identified in several ornamental plantings outside the natural range of the host and south of the general extent of the disease. The disease was reported in similar landscapes outside the general range of the disease. Soil and infected plants moved by the public are a concern because they are a means of transport to new areas for the fungus causing the disease.
In 1994 and 1995, 410 trees were identified with major gene resistance. These identifications increased the number of registered resistant sugar pines to 985 in National Forests in California. Almost 25,000 trees with major gene resistance have been planted at Happy Camp, CA, to determine if they have other forms of resistance. Selections from the oldest of these trees will continue for enlarging clone banks for future breeding and seed production. About 96,000 seedlings are being tested for slow rusting mechanisms at Pondorado High School in Camino, CA.
Work on other susceptible white pines was increased during 1994 and 1995. Seed collected from 89 foxtail pines, 123 whitebark pines, and 100 western white pines will be investigated for resistance.
Research is focused on unraveling the genetic structure of the fungus. By knowing its genetic structure and the nature of the resistance in the trees, the reliability of rust resistance can be predicted for the sugar and western white pines produced by the program. New races of the rust could exist or develop with the potential to overcome the resistance in selected pines. The probability of this development is low because the variation in the rust is low.
Dwarf mistletoe resistance program. Dwarf mistletoes are parasitic seed plants that grow on conifers throughout California. Forest Pest Management and the Genetic Resource Program initiated a search in 1993 for resistance in both ponderosa and Jeffrey pines. The goals of this program are to identify individual trees that show a potential for resistance to dwarf mistletoe; to develop simple guidelines for identifying and evaluating other resistant candidates; to develop and evaluate screening methods for resistant candidates; and to identify the mode and degree of resistance inheritance for candidates and their progeny.
Guidelines have been developed, and 65 ponderosa pines and 35 Jeffrey pines on the Lassen and Plumas National Forests have been selected for possible resistance. In addition, 10 ponderosa pines and 5 Jeffrey pines with heavy mistletoe infections have been identified as highly susceptible controls for comparison. Artificial inoculation with dwarf mistletoe seed was initiated on six of the resistant candidates in 1993. Inoculation test evaluations will begin in 1996.
Annosus root disease. Annosus root disease, which infects a range of conifer tree species and a few hardwoods and shrubs, has been found in all areas of California with conifer hosts (fig. 16). The most important hosts in California include ponderosa pine, Jeffrey pine, white fir, red fir, and incense-cedar. This root disease causes tree mortality, slowed growth, lost site productivity, and decay of the lower bole, depending on the host species. Two strains, or biological species, of annosus have been identified in the state that act differently and have different host species.
Figure 16 — Known locations of annosus
root disease in California.
Not all forest areas suffer the same amount of damage. The damage in true firs is greatest in stands composed largely or solely of true firs. The Sierra Nevada and southern California mountains have the highest incidence of annosus root disease in true firs. Pines suffer the most losses in the eastside pine type of northeastern California and the eastern side of the Sierra Nevada, as well as the mountains of southern California.
Surveys of the forest land in much of California were completed in the 1970s and early 1980s to determine the incidence of annosus root disease. In the 12 National Forests of northern and central California, Slaughter and Parmeter (1989) estimated that almost 2.5 million true firs died between fall of 1977 and summer of 1979. Of this 2.5 million, 634,000 were infected by annosus root disease. The dead infected trees contained an estimated 68 million board feet. This volume was about 5.2 percent of the true fir annual growth. In addition to the dead trees, an estimated 12.3 million live true firs, with a volume of 1.46 billion board feet, were infected.
In 1976, an estimated 60 million board feet of pine mortality was at least partially a result of infection by annosus root disease (Smith 1984). The incidence in live trees is not known, but it is not as substantial as in true firs because of the more rapid mortality in pine hosts.
Annosus root disease causes considerable loss and damage in recreational and developed areas. Mortality and root failure of live trees are the principal concerns. Developed sites were surveyed in the 1970s in Yosemite National Park after considerable damage by annosus root disease. Ponderosa pine and incense-cedar were examined in developed areas of Yosemite Valley, and 102 annosus root disease centers were identified (Marosy and Parmeter 1989). Campgrounds in the pine forests of southern California also have a high incidence of annosus root disease.
Annosus root disease is controlled by preventing infection of freshly
cut stumps by airborne spores of the fungus that causes the disease. Borate
compounds have been found highly effective in protecting freshly cut stumps.
The Forest Service routinely has pine stumps treated in many areas of eastside
pine forests as well as some true fir stands in the transition and westside
zones. In 1994, about 16,600 pounds of material were applied to stumps
on nearly 58,000 acres of National Forest lands. In 1995, the amount used
exceeded 22,800 pounds on about 51,500 acres. This use was mostly for timber
sales, but recreational and developed areas were also treated.
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