©2023 International Society of Arboriculture 4 per label instructions) in holes drilled using a 3/8-in high helical drill bit 5 cm deep at a 45° downward angle every 10.2 cm of circumference at the base of trees. All holes were drilled within 12 in (30.5 cm) of the base of trees, within root flares where visible. Injections were made through #4 Arborplugs® inserted at drill sites such that the Arborplug® barbs created a seal between the inner bark and xylem tis- sue. Trees in the PZOL treatment group were injected in late March 2019, prior to leaf flush, and after allow- ing time for product translocation, HL inoculations were conducted 2 months later (late May 2019). In a few cases it was suspected during drilling that the 5-cm-deep treatment holes terminated or bisected decayed xylem. Given the difficulty in locating acces- sible trees in the project area, alternative trees were not chosen. However, all propiconazole-injected trees were felled following death or in December 2020 at the cessation of the QUIK-jet® Micro-InjectionTM system trial to determine what effect any undetected internal wood decay may have had on treatment effi- cacy. Trees were cut at the plane of injection to expose drill sites and then sanded with increasingly finer grit (80 to 220) with an orbital hand-sander and aged under magnification using a Nikon SMZ445 (8 to 35× mag- nification)(Nikon Metrology, Inc., Brighton, Michi- gan, USA). All trees where greater than 50% of treatment holes bisected decayed wood were excluded from further analyses. Sound wood surrounded all treatment holes within 3 trees, however decayed wood was bisected by a single hole in 3 trees and by 2 holes in 2 trees. Because this did not constitute more than 25% of total treatment sites per tree, we retained these trees for analyses. In one case, each of the 5 total treatment holes in 1 tree penetrated decayed wood, and thus this tree was excluded from analyses. One additional tree in the PZOL + HL treatment was excluded after it was discovered to be naturally infected with laurel wilt at the time of field inocula- tion (HL) based on crown wilting and vascular stain- ing in outer sapwood. Evaluation of TREE I.V. Micro-InfusionTM System (2020–2021) To evaluate the use of propiconazole as a preventive treatment against laurel wilt using the TREE I.V. Micro-InfusionTM delivery system, 42 wild sassafras trees (12.7- to 48.3-cm DBH) were selected in forests within the KNF, LA, USA, as described in the previ- ous trial above, and randomly assigned to either the infusion system results in better translocation of the product than the concentrated treatments delivered using injection systems. While propiconazole is known to protect redbay against laurel wilt for at least 30 weeks (where trees were inoculated with H. lauricola and injected with propiconazole in April)(Mayfield et al. 2008a) using a micro-infusion system, wider appli- cations among Lauraceae species, such as high-value sassafras, and alternative injection systems, such as micro-injection, have not been evaluated. Thus, our primary objective was to evaluate the use of propi- conazole as a preventive treatment against LWD in sassafras using 2 methods of product delivery: the QUIK-jet® Micro-InjectionTM and TREE I.V. Micro- InfusionTM systems, testing the null hypothesis that the time (weeks) elapsed to expression of greater than 50% crown wilt, branch mortality, and/or tree mortality between the propiconazole-injected and H. lauricola- inoculated trees did not significantly differ from trees in the untreated control group. MATERIALS AND METHODS Evaluation of QUIK-jet® Micro-InjectionTM System (2019–2020) To evaluate the use of propiconazole as a preventive treatment against laurel wilt using the QUIK-jet® Micro-InjectionTM system, we selected 34 sassafras trees primarily located in mature oak-pine-hickory forests within Kisatchie National Forest (KNF), Grant and Rapides Parishes, LA, USA. Due to the difficulty of locating readily accessible sassafras trees in the area, a wide range of diameters (12.7- to 40.6-cm diameter at breast height)(DBH) was allowed in the study. The treatments below were randomly assigned with the restriction that treatments were spread evenly across the range of tree diameters. PZOL + HL: tree injected with propiconazole and inoculated with H. lauricola (n = 9) HL: tree inoculated with H. lauricola and not injected with propiconazole (n = 9) AG: tree inoculated with sterile agar and not injected with propiconazole (n = 8) PZOL + AG: tree injected with propiconazole and inoculated with sterile agar (n = 8) Treated trees received propiconazole (Propizol®; Arborjet, Inc., Woburn, MA, USA) formulated at a rate of 10 mL/in DBH (equaling 3.9 mL [0.61 g] per cm; the recommended rate for prevention of LWD Johnson et al: Propiconazole for Prevention of Laurel Wilt Disease in Sassafras
January 2023
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