84 Wyka et al.: Effects of G. clavigera and L. longiclavatum on Western White Pine Arboriculture & Urban Forestry 2016. 42(2): 84–94 Effects of Grosmannia clavigera and Leptographium longiclavatum on Western White Pine Seedlings and the Fungicidal Activity of Alamo® , Arbotect® , and TREE-äge® Stephen A. Wyka, Joseph J. Doccola, Brian L. Strom, Sheri L. Smith, Douglas W. McPherson, Srđan G. Aćimović, and Kier D. Klepzig Abstract. Bark beetles carry a number of associated organisms that are transferred to the host tree upon attack that are thought to play a role in tree decline. To assess the pathogenicity to western white pine (WWP; Pinus monticola) of fungi carried by the mountain pine beetle (MPB; Dendroctonus ponderosae), and to evaluate the potential for systemic prophylactic treatments for reducing fungal impacts, experi- ments were conducted with WWP seedlings to meet three objectives: 1) evaluate pathogenicity of two MPB-associated blue-stain fungi; 2) evaluate phytotoxicity of tree injection products; 3) evaluate the anti-fungal activity of tree injection products, in vitro and in vivo, toward the associated blue-staining fungi. To evaluate pathogenicity, seedlings were inoculated with Grosmannia clavigera or Leptographium lon- giclavatum, common fungal associates of MPB. Seedling mortality at four months aſter inoculation was 50% with L. longiclavatum and 90% with G. clavigera, both significantly higher than controls and thereby demonstrating pathogenicity. Phytotoxic effects of TREE-äge®, Alamo®, and Arbotect® were evaluated by stem injection; no phytotoxic effects were observed. Anti-fungal properties of the same three products were evaluated in vitro against G. clavigera, where Alamo was most active. Co-inoculation of G. clavigera and L. longiclavatum into seedlings aſter a stem injection of Alamo showed significantly less mortality and lesion formation than either species alone. Results support the hypothesis that MPB blue-stain associates, particularly G. clavigera, promote death of WWP when attacked by MPB. These findings suggest that the administration of a fungicide with insecticide for tree protection against bark beetles may be advantageous. Key Words. Bark Beetles; Blue-Stain Fungi; Emamectin Benzoate; Grosmannia clavigera; Leptographium longiclavatum; Mountain Pine Beetle; Pinus monticola; Propiconazole; Systemic Fungicide; Systemic Insecticide; Thiabendazole; Tree Injection; Western White Pine. Dendroctonus ponderosae, the mountain pine bee- tle (MPB), is an aggressive and destructive pest of many pine species in western North America. Lodgepole pine (Pinus contorta Douglas var. lati- folia Engelmann) is a favorite host, while MPB is also a serious pest of ponderosa pine, P. ponderosa Douglas ex C. Lawson, whitebark pine, P. albicaulis Engelmann, western white pine, P. monticola Doug- las ex D. Don, and limber pine, P. flexilis James (Tsuneda and Hiratsuka 1984; Yamaoka et al. 1990; Solheim and Krokene 1998; Carroll et al. 2003; Ono 2003; Lee et al. 2006a). Recently documented MPB outbreaks in western North America have resulted in millions of tree deaths (Carroll et al. 2003; Ono 2003) and reinvigorated interest in control options. Adult MPBs mine the inner bark, moving from the attack site in an axial and planar orientation in ©2016 International Society of Arboriculture host trees. High attack densities and the successful establishment of brood, which mine laterally, result in tree girdling and subsequent host death. Success- ful reproduction by MPB depends on its relation- ship with associated fungi (Raffa and Berryman 1983; Yamaoka et al. 1990; Yamaoka et al. 1995; Six and Paine 1998; Rice et al. 2007b). The three main blue-stain ascomycetes isolated from D. pondero- sae are Grosmannia clavigera (Robinson-Jeffery and Davidson) Zipfel, de Beer and Wingfield [≡ Ophios- toma clavigerum (Robinson-Jeffery and Davidson) Harrington], Ophiostoma montium (Rumbold) von Arx, and Leptographium longiclavatum Lee, Kim and Breuil (Tsuneda and Hiratsuka 1984; Yamaoka et al. 1995; Solheim and Krokene 1998; Kim et al. 2005; Lee et al. 2005; Lee et al. 2006b). These fungi are not only vectored by MPB but are also considered
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