28 (Rainbow TreeCare Scientific Advancements, Minnetonka, MN ). Some effects of paclobutrazol are reduction in shoot growth and stimulation of root development. The triazole-based chemical also has fungicidal activity (Jacobs and Berg 2000; Blaedow et al. 2006). Preliminary evidence suggests that application of paclobutrazol may improve tree health and reduce the effects of plant disease (Anonymous 2002). Paclobutrazol is applied as a soil drench around the base of the tree and is taken up into the tree systemically. Paclobutrazol may not have any effect until the year after the treatments, but its benefits are thought to last for 3 years. One objective of this research was to document the decline of a population of Austrian pines over a 15-year period resulting from Diplodia tip blight. Another objective was to test other chemical approaches as an alternative to spraying the foliage with fungi- cides for reduction of disease levels and/or latent infections. MATERIALS AND METHODS Austrian Pine Tip Blight Survey Austrian pines growing in landscape groupings on the UK cam- pus (38.0° north, 84.5° west), located in Lexington, Kentucky, U.S., were surveyed for tip blight disease during the month of July eight times over 15 years from 1992 to 2007. The first year, each tree was identified according to location and position near campus buildings so that subsequent surveys could be correlated. For each tree, the age was estimated by counting the number of whorls of branches along the main trunk, and an estimate of whole-tree per- cent tip blight (number of dead shoots versus number of total [dead plus live] shoots) was made. In cases where lower branches had been removed as a result of tip blight, age and disease estimates were adjusted accordingly. The presence of D. pinea -infected cones, insect infestations, and abiotic disorders was also recorded. Fungicide Injection for Tip Blight Management Two distinct groups of UK campus Austrian pines were selected for injection treatments. The first experiment was done in a mature (20 to 22 years old) stand of diseased (1% to 50% tip blight) pines and the second experiment was done in a maturing (13 to 14 years old) disease-free stand. Disease symptoms were evaluated in mid- to late summer each year by estimating the per- cent of diseased shoot tips per tree. Diseased branches previously removed for sanitation purposes were included in the estimate. Expt. 1. Sixteen pines located on traffic islands on the UK campus received one of four treatments. Trees were assigned to groups so that each treatment was applied to trees with a similar range of symptoms. Treatments, arranged in a randomized complete block design and replicated on four individual trees, consisted of injections of 1) oxy- carboxin; 2) debacarb; 3) tebuconazole; and 4) water used as a con- trol. Fungicides were used at labeled rates, approximately 14 mg active ingredient per inch tree diameter at breast height. Injections into basal root flares were started when the pine shoot candles were partly elongated on 8 May 1999, 6–9 May 2000, 5 May 2001, and 29–30 May 2002; capsules were removed 4 to 12 days after injec- tion. As a result of the demise and removal of several of the traf- fic island trees in the first year, eight additional 20-year-old trees located around the perimeter of a UK campus parking lot nearby ©2009 International Society of Arboriculture Hartman et al.: Managing Diplodia Tip Blight were injected in May 2000, 2001, and 2002. Trees were grouped into randomized complete blocks, and each treatment was repli- cated five or six times with each replicate being an individual tree. Expt. 2. Forty pines comprising a screen planting on the UK campus were injected in 1999, 2000, 2001, and 2002 as described in Expt. 1. The experiment was designed as a randomized complete block experiment with ten replicates. Recovery of D. pinea from Shoots of Treated Trees In July of 2000, 2001, and 2002, shoot, bud, and needle samples (two each) from asymptomatic and diseased shoots were collected from each treated tree, and the pathogen was cultured on acidified potato dextrose agar (APDA) using standard microbiologic tech- niques. The fungal cultures were identified and confirmed micro- scopically after inoculation of autoclaved pine needles using the method described in Flowers et al. (2001). In Vitro Test of Injected Fungicides Oxycarboxin, debacarb, and tebuconazole were each tested in the laboratory for fungicidal activity against D. pinea and compared with water controls. Fungicides were incorporated into APDA in Petri plates at the following rates: 1, 2, 3, 4, 5, 6, and 1000 ppm. Plugs (4 mm [0.16 in] diameter) of mycelium from actively grow- ing cultures of D. pinea were transferred to the plates. Radial growth from the original plug was measured after 4 days. The test was replicated four times, and the lowest fungicide concen- trations that prevented fungal growth in the experiment were cal- culated as effective doses. Paclobutrazol Basal Drench for Tip Blight Management Suspensions of paclobutrazol were applied at label rates (3.7 g [a.i.]/2.5 cm diameter at breast height) to the bases of 20 mature (17 to 19 years old) Austrian pines growing in a screen planting on the UK campus in July 2003. A shallow encircling trench was carved into the soil adjacent to the trunk and buttress roots of each tree and the paclobutrazol suspension was distributed uniformly into the trench. After the suspension had soaked in, trenches were covered with soil. The experiment, established in a randomized complete block arrangement, was replicated five times with each replicate consisting of four trees per treatment. The pines selected for this experiment had varying levels of tip blight disease rang- ing from 1% to 30% dead tips, and each block of trees contained trees with a similar range of symptoms. An equivalent number of experimental controls were treated with water. Pines were evaluated in July of 2004, 2005, and 2006 for lev- els of tip blight disease, detection of latent infections using PCR assays (Flowers et al. 2003), tree survival, and treatment effects on tree shoot length and trunk diameter. RESULTS Austrian Pine Tip Blight Survey In 1992, the survey identified 486 Austrian pines on the UK cam- pus, with an average age of 15.1 years, distributed among 47 landscape groupings. Of these, 37 trees were lost to construction in subsequent years, leaving 449 trees to be monitored for the entire 15-year period. From the original 449 trees, 377 (84%)
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