Arboriculture & Urban Forestry 35(1): January 2009 Arboriculture & Urban Forestry 2009. 35(1):27–32. 27 Managing Diplodia Tip Blight of Landscape Austrian Pines John R. Hartman , Lisa J. Vaillancourt , Jennifer L. Flowers , and Amy M. Bateman Abstract. A long-term survey of 449 Austrian pines growing on the University of Kentucky campus revealed that Diplodia tip blight disease killed 84% of the trees during a 15-year period and that the pines developed increasing levels of disease as they aged. Treatments consisting of the fungicides oxycarboxin, debacarb, or tebuconazole or water were injected into the lower trunk and root flare of individual trees in a block of mature, diseased pines for 4 years. The fungicide treatments did not significantly affect dis- ease levels. The causal fungus could be isolated readily from diseased and symptomless shoots regardless of the treatment. Diplodia pinea was very sensitive to tebuconazole and debacarb in in vitro fungicide tests. Basal drenches with paclobutrazol affected shoot growth but did not significantly reduce tip blight disease levels or tree mortality. Under midsouth United States climate conditions, Diplodia tip blight of Austrian pines is destructive and very difficult to manage. Key Words. Diplodia pinea ; fungicide basal drench; fungicide injection; Pinus nigra ; Sphaeropsis sapinea ; Sphaeropsis tip blight. Austrian pine ( Pinus nigra ) is widely planted in landscapes throughout the central and eastern United States. Introduced from Europe almost 250 years ago, the tree is valued for its ability to withstand urban growing conditions while providing a pleasing dark green appearance whether used as a specimen plant or as part of a landscape screen. Austrian pines typically grow to a height of 10.6 m (35 ft) to 15.2 m (50 ft) within 20 or 30 years, but can attain twice that height during their lifetime (Dirr 1998). Of the 3,000 to 4,000 trees growing on the University of Kentucky cam- pus in recent decades, at least 10% have been Austrian pines. Diplodia tip blight, also known as pine tip blight or Sphaeropsis tip blight, is a serious disease of conifers worldwide. The fun- gal pathogen, Diplodia pinea (syn. Sphaeropsis sapinea ), causes Diplodia tip or shoot blight (previously known as Sphaeropsis tip blight), which is especially devastating to two-needled pines such as Austrian pine (Sinclair and Lyon 2005). Exotic pines such as Austrian, Mugo, and Scots pines were found to be more suscepti- ble to tip blight than United States native pines (Waterman 1943). Diplodia tip blight disease of Austrian pine is enhanced under stressful growing conditions found in urban landscapes such as drought (Bachi and Peterson 1985). A preliminary survey of more than 400 Austrian pines on the University of Kentucky campus showed that Diplodia tip blight disease progressively worsened as Austrian pines in the land- scape aged (Hartman et al. 1995). Further analysis revealed that almost 40% of symptomless Austrian pine shoots harbored latent D. pinea infections (Flowers et al. 2001), which were probably kept in check by tree defenses (Flowers et al. 2006). Latent infec- tions may convert to pathogenic ones when trees are stressed. D. pinea was recovered from symptomless needles, stems, buds, immature cones, and male flowers. In symptomless stems, the fungus was recovered more frequently from bark and phloem tissues than from the xylem and pith. A polymerase chain reac- tion (PCR) test was developed to detect D. pinea in pine tissues (Flowers et al. 2003) to eliminate the requirement for destructive sampling needed to grow the pathogen in culture. Success in management of Diplodia tip blight with chemical applications of fungicides to the foliage has been inconsistent. Disease was reduced significantly with Bordeaux mixture applied early in the growing season (Peterson 1977). In that study, trees were found to be most susceptible during the early part of shoot (candle) elongation before needles began to elongate. Based on these findings, a standard recommendation suggesting three springtime applications of fungicide, the first at bud swell, the second as the candles are elongating but just before needle emer- gence, and the third as needles are emerging from the needle sheaths, was developed. This protocol is generally indicated on the labels for fungicides containing thiophanate methyl such as Topsin-M 70 WP (Cerexagri-Nisso, King of Prussia, PA) or 3336 WP (Cleary Chemical Co. , Dayton, NJ). A fungicide application schedule consisting of only two early spring sprays has also been advocated (Tisserat 1993). However, grounds managers reported that a protocol involving foliar application of fungicides was not working on the University of Kentucky (UK) campus and else- where (Hartman et al. 1995), possibly as a result of inadequate spray coverage for large trees or imprecise timing resulting from needing to spray large numbers of individual trees over a large landscape during a narrow application window. Furthermore, on institutional landscapes such as the UK campus, application of foliar fungicides is complicated by concerns about human and environmental exposure. To minimize these chemical exposure concerns, systemic fun- gicides can be delivered throughout trees by injecting the chemi- cals directly into small, shallow holes in the outer xylem of the root flare. This provides uniform chemical distribution while minimizing wounding effects and promotes wound closure after injection (Stipes 1988). Fungicide injections have been used for management of canker diseases (Helton and French 1962; Helton and Harvey 1963; Elliott and Edmonds 2008). Oxycarboxin, a phenylamide (Carboject, no longer available), debacarb, a ben- zimdazole (Fungisol ), and tebuconazole, a sterol biosynthesis inhibitor (Tebuject) (Mauget, Inc.) are examples of fungicides that can be injected into trees . Paclobutrazol is a plant growth regulator chemical that inhibits synthesis of the plant hormone gibberellin. For the arboricultural industry, paclobutrazol is sold under the trade name Cambistat ©2009 International Society of Arboriculture
January 2009
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