The Lack of a Long-Term Growth Effect of Annosus Control in Southeastern United States

An evaluation of basal area increment was made in 1988 of six pine plantations located across the southeastern United States. These plantations had been thinned in 1969-1970 and stumps treated with borax to measure long-term efficacy of annosus root rot control. In the present study, no long-term growth effects were identified. There were neither negative growth effects of residual infection in surviving trees nor were there positive growth effects in trees which were released as a result of tree mortality. These results suggest that effects of inoculation and control treatments may have been limited only to those trees which died as a result of infection center development following thinning. Annosus root rot, which is caused by Heterobasidion annosum (Fr.) Bref., is potentially destructive on southern pines growing on high-risk sites. Root contacts and grafts are abundant among closely spaced plantation trees. When these trees are thinned, stumps are colonized by H. annosum, which continues to colonize the root systems of the thinned trees and eventually the roots of adjacent living trees. Affected trees may either be killed after several years or suffer growth loss (Alexander and others, 1981). An important control measure recommended for plantations on high risk sites at the first thinning is to treat the freshly cut stump surfaces with borax. The boron ion is toxic to germinating spores of many fungi, including H. annosum. As the toxic effects of the boron gradually leach away, soil-borne saprophytic fungi quickly invade the stump and H. annosum is unable to compete. The beneficial effects of borax in southern pine plantations were first observed by Driver (1963) and subsequently shown by Hodges 1 Presented at the Symposium on Research and Management of Annosus Root Disease in Western North America, April 18-24, 1989, Monterey, California. 2 Professor and Lecturer/Statistician, respectively, Department of Forestry, Clemson University, Clemson, SC 29634-1003; and Plant Pathologists, respectively, Forest Pest Management, USDA Forest Service, Southern Region, Atlanta, GA 30367. D. A. Starkey (1970) to reduce stump colonization by H. annosum up to 18 months after treatment. In 1969, a southwide pilot project was begun to compare the effectiveness of four promising treatments to prevent annosus root rot in thinned southern pine plantations (Phelps and others, 1970). Stump treatments included application of borax, sodium nitrite, Peniophora gigantea, summer thinning, and a check. In addition, the effects of heavy disease pressure were explored by artificially inoculating H. annosum on some plots. The project was a cooperative effort among state forestry agencies, private landowners, and the USDA Forest Service Southeastern Forest Experiment Station, and Southeastern Area Forest Insect and Disease Management. A summary of results obtained for the period 1969 through 1977 indicated that, although positive effects were not always evident at some locations, borax provided the most effective and consistent protection against stump surface colonization, residual tree infection, and tree mortality (Weiss and others, 1978). No attempt was made at that time to translate residual tree infection and mortality into growth or volume losses. In 1988, we reevaluated the study and discussed the possibility of taking a final look at the plots before they were lost. Several plots had already been lost, either to natural calamities or to harvesting, and the remainder were approaching final harvest age. Owing to limited survey resources, we decided to examine only the effects of borax treatments in combination with inocula­ tions of H. annosum, which were basically the worst case and best case scenarios. Our objective was to determine if radial growth patterns showed that root disease depressed growth in surviving trees, and if borax stump treatment ameliorated these possible negative growth effects. MATERIALS AND METHODS Plots were reexamined at six locations (fig. 1). Plot locations and tree species were: Del Rio, Tenn., and Marion, Va., eastern white pine (Pinus strobus L.); Shelby, N.C., Mineral Springs, Ark., and Lexington, Tenn., loblolly pine (P. taeda L.); and Jasper, Tex., slash pine (P. elliottii Engelm.). The treatments compared were: USDA Forest Service Gen. Tech. Rep. PSW-116 117 Figure 1--Location of plantations used in the annosus root rot stump treatment pilot project. Circled locations were selected for the present study. Code Designation_____________ Treatment ______________ A-U Borax, not inoculated with H. annosum A-I Borax, inoculated with H. annosum E-U Check, not inoculated with H. annosum E-I Check, inoculated with H. annosum The two available replicate plots for each treatment for each location were sampled. When originally established in 1969-1970, plots were 93.4 ft (28.5 m) square with a 15-ft (4.6-m) wide buffer on each side. Steel rods marked the corners of the buffer zones. Maps were made of each plot, showing the compass bearings of the sides, and plot trees were identified with aluminum tags fixed with aluminum nails about 8.2 ft (2.5 m) above ground. Each plot center was reestablished 87 ft (26.5 m) from a corner rod on a bearing that bisected the corner angle. If rods could not be located, the plot center was estimated by measuring 66 ft (20.1 m) on the same bearing from the tagged tree closest to the true corner location. All pines and hardwoods with diameter at breast height (DBH) 2 5 in (12.7 cm) and within a 33-ft (10.1-m) radius of plot center were counted to determine the number of trees per acre. This radius ensured that all plot trees were within the original plot without encroaching on the buffer zone. About 40 percent of the original plot area was used to calculate volume and stocking. Basal area was calculated by measuring the stem diameters of those trees. Heights were measured for all pines within the 33-ft (10.1-m) radius and were to be used in volume calculations. The 10 pines closest to the plot center and within a 40-ft (12.2-m) radius of the plot center were sampled for radial growth analyses. In cases in which a road went through a plot, trees with crowns bordering the road were not sampled. If fewer than 10 eligible trees were found inside the 40-ft (12.2-m) radius, extra trees were sampled on the treatment plot's replicate. For example, if only 6 trees could be sampled on plot E-I-1, then at least 14 trees were sampled on plot E-I-2. Increment cores to the pith were removed at 4.5 ft (1.4 m) from ground level on the north and south faces of each of the 10 sampled trees. After being dried, the cores were glued into grooves in wood blocks, and a flat surface was sanded on each to prepare a transverse face suitable for measurement of annual ring widths. After cores were cross-dated, width of each annual ring was measured to 0.01 mm with a Bannister increment-measuring machine. The raw annual increment data were then converted to annual basal area increments (BAI) for each tree which were then averaged for each plot for the pretreatment period (prior to 1969) and the posttreatment period (1970-1979). These plot averages were then analyzed by using analysis of variance, and the means were subjected to Tukey's means separation technique. Contrasts were also constructed in which data from the borax treatment plots were compared to those from the check treatment plots, and data from plots inoculated with H. annosum were compared to those from plots that had not been inoculated. The variables of interest were the average BAI of pretreatment, the average BAI of posttreatment, and the average change in BAI between the pretreatment and posttreatment measurements. Because each location also repre­ sented a different tree species and stand age, the analyses were done separately for each location and location data were not combined for a pooled analysis.