90 Wyka et al.: Effects of G. clavigera and L. longiclavatum on Western White Pine circumference for G. clavigera, L. longiclavatum, Alamo/blue-stain inoculation, and inoculated checks combined, respectively (Table 4). Gir- dling was significantly greater for seedlings inoculated with G. clavigera than for the other inoculation treatments and the pooled con- trols. Axial lesion lengths were greatest in G. clavigera–inoculated seedlings, followed by L. longiclavatum, Alamo/blue-stain, and controls (4.8 ± 0.5, 2.3 ± 0.4, 0.7 ± 0.1, and 0.6 cm ± 0.1 SE, respectively) (Table 4). Dissections re- vealed that G. clavigera and L. longiclavatum inoculations had oxidized and brownish-blue discolored resin ducts, parenchyma ray cells, and phloem, while the sterile agar and wa ter controls exhibited clear, light-colored sap- wood and healthy phloem (Figure 1). The Alamo/blue-stain-inoculated seedlings also showed clear-light sapwood and healthy phlo- em, except for the dead seedlings, which ex- hibited dark vascular lesions matching those observed from G. clavigera and L. longiclava- tum. Cross sections above and within the inoc- Table 3. Percent foliar dieback in pathogenicity and phytotoxicity studies; means and standard errors (SEs) for each treatment are based on 10 seedlings, except for the inoculation controls (where the average of water and sterile agar treatment means and appropriate SE are reported). Study Pathogenicity Treatment Alamo/B.S. G. clavigera L. longiclavatum Pooled controls Phytotoxicity TREE-äge Alamo Arbotect UTC Foliar dieback (%) Mean ± SE 20.8 ± 9.2 bz 91.0 ± 9.0 a 56.7 ± 14.5 ab 20.5 ± 7.9 b 13.5 ± 1.8 a 19.6 ± 3.2 a 25.0 ± 4.2 a 30.2 ± 8.5 a z Treatments within a study with the same letter are not significantly differ- ent based on Tukey adjusted P-values. ulation site of the controls indicated successful compartmentalization of incision wounds. Grossmannia clavigera and L. longiclavatum, identified by morphological analysis, were recovered from the excised cross sections. Phytotoxicity of fungicides After 120 days, mortality of seedlings treat- ed with TREE-äge, Alamo, Arbotect, or un- treated checks was 0%, 0%, 0%, and 10% mortality, respectively (Table 1), giving no indication 1.98, P = 0.135) among the untreated controls, TREE-äge, Alamo, and Arbotect treatments, with 30.2 ± 8.5, 13.5 ± 1.8, 19.6 ± 3.2, and 25.0% ± 4.2 SE, respectively (Table 3). No foliar phytotoxicity was therefore observed due to application of any systemic chemistry at the rates used. Microscopic examination confirmed that discolored sapwood was pres- ent and limited in the TREE-äge, Alamo, and Arbotect treatments; resin ducts and phloem were neither oxidized nor necrotic. Cross sec- tions of a single untreated control seedling that died had oxidized xylem and an unidenti- fied infection, while all other untreated con- trols had clear sapwood and healthy phloem. Experiment #2 Dual inoculation of G. clavigera Inoculations of G. clavigera on both sides of seedling stems resulted in 91.0% ± 9.0 SE seed- ling mortality, compared to 0.0% of the sterile agar controls. G. clavigera was identified by mor- phological characteristics and was re-isolated from cross sections of inoculated seedlings. Table 4. Pathogenicity of inoculation treatments as measured by percent stem girdling and lesion length (cm). Treatment N Pathogenicity Alamo/B.S. G. clavigera L. Longiclavatum Pooled controls 10 10 6 8 Circumferential girdling (%) Mean ± SE 38.7 ± 5.7 bz 92.0 ± 5.7 a 51.8 ± 7.4 b 28.9 ± 6.4 b z Treatments with the same letter are not significantly different based on Tukey-adjusted P-values. y Mean separation results are based on analysis of log-transformed lesion heights. Lesion length (cm) Mean ± SE 0.7 ± 0.1 czy 4.8 ± 0.5 a 2.3 ± 0.4 b 0.6 ± 0.1 c treatments and control (FET, P = 1.0). Foliage necrosis did not differ significantly (F3,36 of differences among pesticide = ©2016 International Society of Arboriculture
March 2016
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