30 Table 1. Isolation of Diplodia pinea from University of Kentucky campus Austrian pines. z Expt. 1 Percent recovery of D. pinea Treatment 2000 y 55 a Symptomless shoots with D. pinea Debacarb Tebuconazole 40 a Water 67 a Expt. 2 Percent recovery of D. pinea 2001 2002 2000 2001 2002 Treatment 50 a 70 a 8 a 17 a 32 a 50 a 88 a 18 a 30 a 20 a 60 a 80 a 23 a 25 a 45 ab Oxycarboxin 46 a 100 a 75 a 25 a 26 a 55 ab Diseased shoots with D. pinea Tebuconazole 75 a 100 a 100 a 69 b 87 b 90 bc Water Debacarb 79 a 100 a 100 a 75 bc 94 b 100 c 80 a 100 a 100 a 79 bc 100 b 100 c Oxycarboxin 67 a 100 a 100 a 88 c 93 b 100 c z yielding D. pinea in culture (ten samples per tree). y Expt. 1, mature severely diseased Austrian pines (four to six replicates). Expt. 2, maturing Austrian pines with lower levels of disease (ten repli- cates). Both treated with fungicides by trunk injections. Percent shoots Means in a column followed by the same letter are not significantly dif- ferent; Waller-Duncan K-ratio t-test (K = 100, P = 0.05). DISCUSSION Austrian Pine Tip Blight Survey In one study of nine “old” and four “young” open-grown Austrian pines in Illinois, the age of the “old” trees averaged 73 years and the “young” trees averaged 27 years (Minckler 1955). Based on our survey, the Austrian pines on the UK campus do not last nearly as long as this, rarely living more than 30 years. In Florida, Diplodia tip blight is reported to disfigure Austrian pines at approximately 25 to 30 years of age (Gilman and Watson 2006) and in Kansas, at approximately age 30 years (Tisserat 1993). This is more in line with our observations; during the 15 years of the UK campus survey, Austrian pines were so disfigured or killed by Diplodia tip blight that they generally needed removal by approximately age 25 to 30 years. During the 15-year interval, frequent summer dry periods and drought (1994, 1999, 2002, 2005, and 2007) could have contributed to increased disease susceptibility of landscape Austrian pines. Pine wilt disease caused by the pine wood nematode, Bursaphalenchus xylophylis , was found in one dying tree but was not considered a major cause of Austrian pine death in this survey. Fungicide Injection for Tip Blight Management The in vitro test of the fungicides used for injection against Diplodia pinea suggest that two of the fungicides, debacarb and Table 2. Effect of different concentrations (in parts per mil- lion) of fungicides on in vitro growth of D. pinea (in millime- ters) after 4 days growth on acidified potato dextrose agar amended with fungicide. Fungicide and concentration 1 ppm 2 ppm 3 ppm 4 ppm 5 ppm 6 ppm 1000 ppm Tebuconazole 0 Debacarb 0 0 0 66 64 38 23 0 8 0 0 0 0 Oxycarboxin 68 66 63 67 68 65 0 Water 64 63 69 65 64 67 65 ©2009 International Society of Arboriculture In a column, means bearing the same letter are not significantly different (Waller-Duncan K-ratio test, P = 0.05). Paclobutrazol Water z tebuconazole, might have sufficient activity to manage Diplodia tip blight. Tebuconazol is not labeled for management of pine diseases and although debacarb is labeled for use in managing other tip blight and canker diseases of trees, it is not labeled for Diplodia tip blight of pines. Fungicide injections neither “cured” pines of Diplodia tip blight disease nor did it prevent symptomless trees from devel- oping tip blight. In the latter case, it is possible that latent infec- tions were already prevalent and that the fungicides were not distributed to these latent infection sites because of blocking by necrophylactic periderm (Flowers et al. 2006). Under stress such as drought, latent infections may be able to convert to pathogenic ones. Injection with debacarb appeared to slow the progress of tip blight in already diseased trees, but this trend was not statistically significant as a result of highly vari- able disease levels between trees and as a result of loss of some trees to tip blight before the experiment was completed. In the younger, less diseased pines, disease progress was not affected by debacarb. In both experiments, fungicide injections did not reduce the presence of latent infections. Latent infec- tions in the younger Expt. 2 trees increased over time probably because the pathogen becomes more available on infected cones over time. During the injection process, some of the capsules quickly filled with pitch from the tree. Thus, it is difficult to know whether all capsules were actually emptied into the injection sites. Our results are not encouraging for arborists who would like to use fungicide injections for Diplodia tip blight management in Austrian pines. Other research trials on injection of systemic fungicides for tip blight management have been inconclusive (Tisserat 2004). Basal Drench for Tip Blight Management Tip blight percentages suggest that Diplodia tip blight develop- ment was slowing down in paclobutrazol-treated pines at the end Table 4. Effect of paclobutrazol on Austrian pine tree growth in 2005. 1-year trunk Treatment diameter increase in cm (in) z In a column, means bearing the same letter are not significantly different (Waller-Duncan K-ratio test, P = 0.05). Paclobutrazol 0.7 (0.3) a Water z 1.0 (0.4) a 1-year shoot terminal growth in cm (in) 12.5 (5.0) a 15.8 (6.3) b 1-year lateral branch growth in cm (in) 10.3 (4.1) a 11.3 (4.5) a Hartman et al.: Managing Diplodia Tip Blight Table 3. Effect of paclobutrazol application in 2003 on subse- quent Austrian pine tip blight disease incidence, presence of latent Diplodia pinea infections, and tree survival in a land- scape screen planting. 2005 results Percent tip blight z 22.1 a 33.7 a 2006 results Percent shoot tips with latent D. pinea infections 96 a 59 a Percent survival of pines 65 a 45 a
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