Borax Stump Treatment for Control of Annosus Root Disease in the Eastside Pine Type Forests of Northeastern California

A historical perspective and description of recent studies on the use of borax to treat pine stumps against infection by Heterobasidion annosum in eastside pine stands of northeastern California are presented. The studies indicate that boraxing of pines in eastside pine stands is an effective means of preventing annosus infection. Data and observations suggest that the lower stump diameter limit for treating chain saw-cut pines with borax could be raised from the currently recommended 8 inches (20.3 cm) to about 16 inches (40.6 cm) with little or no risk of creating active annosus root disease centers. The eastside pine type forests of northeastern California lie in the region east of the Sierra Nevada-Cascade crest between the 4,000 and 6,500 foot (1220 and 1982 meter) elevations (fig. 1) where the climate is cold and dry and the principal tree species are ponderosa pine and Jeffrey pine (McDonald 1983). Other vegetation consists of varying amounts of western juniper, sagebrush, grasses, and occasional mountain mahogany. The incidence of Heterobasidion annosum in eastside pine type stands is especially high and locally damaging (Olson 1941; Wagener and Cave 1946), due to past heavy cutting of pines and an apparently favorable environment for the pathogen. Work by Bega and Smith (Bega and Smith 1966; Smith and others 1966) supported earlier statements of Meinecke (1914) and Wagener and Cave (1946) that increased forest management activity has contributed to an increased incidence of annosus root disease, with the greatest losses being associated with pine stumps left after thinning and harvest cutting operations. This paper briefly discusses the history of the use of borax to treat tree stumps against infection by H. annosum in California, describes some recent studies on the incidence of annosus root disease in eastside pine type stands in relation to the use of borax and stump diameter, and concludes with a summary of the current status of borax use. Presented at the Symposium on Research and Management of Annosus Root Disease in Western North America, April 18-21, 1989, at Monterey, Calif. Supervisory Plant Pathologist, Pacific Southwest Region, U.S. Department of Agriculture, Forest Service, San Francisco, Calif. Figure 1. The eastside pine type forests of northeastern California lie in the area east of a line extending from Lake Tahoe northwestward to Highway 5 at the Oregon border. HISTORICAL PERSPECTIVE Recommendations for direct suppression or prevention of annosus root disease in California, based on research and surveys by Pacific Southwest Forest and Range Experiment Station and Pacific Southwest Region pathologists, were formulated in the 1960's. Direct suppression attempts in an area of highvalue pines, which involved the pulling of stumps and fumigation (Bega 1962), proved too costly and impractical in most forest situations. Other control possibilities were suggested, but these either showed no promise under California conditions (biological control) or were not adequately field tested (the clear felling of trees around disease centers). A silvicultural control method, which involved thinning during warm, dry periods unfavorable for growth of the fungus, was developed for eastside pine stands by R.S. Smith, Jr. (unpublished data). High stump temperatures inhibited or blocked stump colonization by H. annosum in studies done in the southeastern Unites States (Gooding and others 1966; Ross 1973). Smith monitored stump Unpublished data on file, Pacific Southwest Region, U.S. Department of Agriculture, Forest Service, San Francisco, Calif. USDA Forest Service Gen. Tech. Rep. PSW-116 159 temperatures of cut and inoculated ponderosa pine saplings and poles on the Lassen National Forest. Assays of discs cut from the stumps suggested that H. annosum will not survive the summer in stumps less than 6 inches (15.2 cm) in diameter because lethal temperatures above 104oF (40oC) are reached in the tops of the stumps. Preventive measures such as chemical treatment of freshly cut stumps also were investigated in the 1960's. Choice of chemicals to test was based on success elsewhere (Berry and Bretz 1964; Hodges 1970; Driver 1963). High-nitrogen compounds (urea, ammate) that stimulate competing fungi, and borax, which is toxic to H. annosum spores, were tested in 1965 and 1966 on the Lassen National Forest. Results were inconclusive. In 1969, Graham (1971) demonstrated that treatment of 2to 6-inch diameter Jeffrey and ponderosa pine stumps in young eastside pine stands on the Lassen National Forest with technical grade borax (sodium tetraborate decahydrate) prevented infection. After artificial inoculation with the fungus, less than 1 percent of the borax-treated stumps became colonized, but over 61 percent of the similarly inoculated but untreated control stumps became colonized. In 1969, Smith (1970) demonstrated that dry granular borax also prevented infection of white fir stumps, and did so to a greater degree than did a mixture of borax, water, and sticker. By the early 1970's, observations and research discussed above had resulted in an accepted list of control recommendations, with the realization that prevention by treatment of freshly cut stumps with borax was the best recourse. In developed recreation sites, high-use areas, and areas with high-value trees such as seed orchards, treatment of stumps of all conifer species with dry granular borax immediately after felling was recommended because of the assumed high value of the trees. In timber stands, the use of borax needed to be justified by weighing the dollar cost of control against the dollar value of losses prevented. Treatment of all pine stumps during thinning or timber sales was recommended if damage by the fungus had been established. True fir was not included in the recommendations for borax treatment in timber stands for several reasons, not the least of which was the low stumpage value of the species. Other reasons included the knowledge that H. annosum infects true fir through wounds as well as through stump surfaces, and the lack of pilot testing to demonstrate cost effectiveness on an operational basis. Pacific Southwest Region pathologists (Byler and others 1978) developed a survey and subsequent benefit/cost analysis procedure to determine if application of borax to pine stumps is economically justified in eastside pine type stands. The procedure involves a strip cruise of a proposed sale area to determine the proportion of stumps from previous cuttings that had become annosus infection centers. The assumption is made that, without treatment, the proportion of stumps that become infected and cause mortality centers in the upcoming sale will be similar to that of previous sales. Data collected are used to calculate the economic feasibility of borax treatment of stumps created from the proposed timber sale. The benefit of borax treatment is the product of the estimated impact resulting from the sale, the effectiveness of borax stump treatment (assumed to be 90 percent) and a present net worth factor (based on the discount rate and the number of years until harvest). A summary of the procedure follows: BENEFIT/COST ANALYSIS FOR BORAX STUMP TREATMENT 1. IMPACT = A x B x C x D x E where: A = number of trees to be cut B = Pct stumps currently infected C = average center size (acres) D = yield at rotation (M bd ft) E = present stumpage value ($/M bd ft) 2. BENEFIT/COST = IMPACT x F x G