IMPACTS OF WHITE PINE BLISTER RUST1
Brian W. Geils2
1Presented by invitation before the
12th USDA Interagency Research Forum on Gypsy Moth and Other Invasive Species
16–19 January 2001; Annapolis, Maryland
2USDA Forest Service, Southwest Forest Science Complex
2500 South Pine Knoll Drive, Flagstaff, AZ 86001
Citation: Geils, B.W. 2001. Impacts of white pine blister rust. in: Fosbroke, S.L.C.; Gottschalk, K.W., eds, Proceedings, U.S. Department of Agriculture interagency research forum on gypsy moth and other invasive species 2001; 2001 January 16–19; Annapolis MD. Gen Tech. rep NE-285. Newton Square PA: U.S. Department of Agriculture, Forest Service, Northeastern Research Station: 61–64.
The introduction of Cronartium ribicola Fisher to North America early in the 1900s began the first major forest disease outbreak American forestry seriously confronted. White pine blister rust has caused significant impacts in eastern North America, the Lake states, Pacific and Rocky Mountain forests. Blister rust is still a damaging pathogen and important ecological factor in forests of those regions. It is now spreading in the Great Basin, Southern Rocky Mountains, and Southwestern forests, and may soon reach northern Mexico (if it has not already). Because white pines are so highly valued, their loss to blister rust and our efforts to mitigate those losses have generated incalculable impacts—socio-economic, political-administrative, ecological, scientific, and aesthetic. The history of blister rust in North America has already gone through two management cycles (eradication and integration), and I propose it is entering a third (adaptation).
Before blister rust was discovered in 1906 in Geneva, New York, forest pathologists knew of its destructive potential to American white pines (Spaulding 1922, 1929). American white pines had been planted widely across cool, moist Europe where nearly every rural family cultivated black currant. When Cronartium ribicola was introduced from Asia, it found both a suitable environment and the two hosts it required to complete its lifecycle: white pines and ribes. The disease eventually caused European foresters to abandon the highly susceptible white pines. In America, however, forestry was white pine forestry. When the white pine of a region was exhausted, logging moved west. The timber industry had just set up in the Pacific and Inland Empire forests of western white pine and sugar pine. In the East and Lake states, replanting eastern white pine was underway using cheap and plentiful nursery stock from Europe. By the time the rust was discovered, it was already widely established [and damaging small and large trees]. There had not been much which could be done to prevent the other catastrophic outbreak of the times, chestnut blight. But, white pines were worth saving (Pack 1933); and this pathogen had a weakness (Spaulding 1922). [Disease development requires a virulent pathogen + susceptible host + favorable environment and ribes is a required host.] The first attack on blister rust consisted of quarantines (especially to keep the rust out of western North America) and eradication (first, cultivated black currant and then wild ribes). Some of the first impacts of blister rust were political-administrative—passage of our first quarantine and weed laws and regulations and the first organization of agencies and cooperative federal-state programs dealing with forest pests (Maloy 1997). The laborers employed in ribes eradication not doubt saw the opportunity as an economic boon (especially during the Depression when the eradication program reached its peak in employment and expenditure).
In the Eastern states, conditions were especially suitable for ribes eradication to succeed and it continues to be effective for protecting young plantations (see Lombard and Bofinger 1999; Ostrofsky and others 1988). Ribes were plentiful in the Lake states and could be removed with reasonable effort. Regional and landscape features, however, made the environment for the rust more variable (Charlton 1963, Van Arsdel 1961). Where conditions were not suitable for infection, ribes eradication was not economically efficient (Anderson 1973). Although the Office of Blister Rust Control (BRC) was dedicated to ribes eradication, the strategy was severely tested in the West (Benedict 1981). In eastern Washington, northern Idaho, and western Montana, wild ribes were not only important sources of rust inoculum, they were large and abundant (Mielke 1943). Considering transportation and labor, eradication became of a Herculean task, met by a determined BRC with chemicals, heavy machinery, and explosives.
Although some of the first research in biological control was undertaken, managers were mostly concerned with improving the efficiency of eradication. Accomplishments were reported as acres treated. In some areas only a few white pines survived exposure to the rust; many were salvaged. Control probably did reduce the velocity and severity of the outbreak. Research was begun on hazard rating (Van Arsdel 1961), genetic breeding (Bingham 1983), and silvicultural control. With improvements in fire suppression, reserve crews of rust busters were no longer needed. Eradication moved to areas of marginal benefit (Toko and others 1967). The crisis for the BRC was probably the deployment of an antibiotic strategy without an adequate understanding of canker development and without controlled, replicated testing (Leaphart and Wicker 1968). Not only was the blister rust program was re-organized under the Forest Service, but the entire strategy of forest disease control shifted to integrated management as a part of forest operations.
The rust outbreak and salvage created new conditions. Other forest tree species came into economic and ecological importance. Successional changes and new disturbance regimes required foresters to deal with new pests—defoliators, bark beetles, and root diseases. The rust spread into the Sierra Nevada and high-elevation pines of the Northern Rockies. Supported by new research (McDonald and others 1991), new approaches were developed for integrating pest management into forest practice (Hagle and others 1989). Tactics included: silviculture to reduce regeneration of ribes (Moss and Wellner 1953), genetically-improved planting stock, thinning and pruning (Hunt 1998), and decision-support tools (McDonald and others 1981). The paradigm of this era was "if we can quantify the economic costs and ecologically impacts of forest pests, we can implement appropriate, intensive-management policies". Unfortunately, this approach did not adequately consider "surprises" (Holling and Meffe 1996) and change in ecosystems and institutions (Gunderson and others 1995). Although the rust in North America begun with a genetic bottleneck (Hamelin and others 2000), it seemed to be evolving (McDonald 1996). Society’s demands from public forests also raised the importance of biological diversity and ecological sustainability. Forest insects and pathogens were no longer viewed as "pests", they were "natural disturbance agents".
Cronartium ribicola is an exotic, invasive species which has proven capable of instigating catastrophic ecological change. Our challenge is to design research for and adapt management for a dynamic, un-predictibable environment. The issues are likely to include impacts in sensitive ecosystems and to dependent species (Hoff and Hagle 1990), bridging genetic barriers of the rust (e.g., by introduction of new Asian races), accommodating the cultivation of ribes (Hummer and Sniezko 2000), and expansion of the rust into new regions (such as Mexico). Our most important tool will no longer be the hodag (developed for eradication) but communication and cooperation.
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