Arboriculture & Urban Forestry 37(6): November 2011 interest to increase our knowledge about the breadth of im- pacts that systemic fungicides may have. Two experiments were conducted, the first to screen three products for their sys- temic activity against O. minus in loblolly pine, and the second to more rigorously assess the most effective product when ap- plied alone and in combination. The three fungicides select- ed were Alamo® Protection, LLC, Greensboro, North Carolina, U.S.), Arbo- tect® 289 (14.3% Propiconazole w/w, Syngenta Crop 20-S (20% 2-(4-thiazolyl) benzimidazole w/w, Syngenta Crop Protection, LLC, Greensboro, North Carolina, U.S.), and PHOSPHO-jet (45.8% Mono-and di-potassium salts of phos- phorous acid w/w, Arborjet, Inc., Woburn, Massachusetts, U.S.). METHODS In both experiments, treatments were assigned in a completely randomized design to loblolly pines growing in central Louisiana (Winn Ranger District, Kisatchie National Forest). Researchers injected each selected tree around its base with the systemic fun- gicide using the Tree I.V. system and Arborplugs™ (Arborjet, Inc. Woburn, Massachusetts, U.S.), with an injection point targeted at every 10 cm basal circumference. It was assumed that fun- gal inoculations within a tree were independent (Klepzig et al. 2005), which allowed for multiple sample periods over time (Fig- ure 1; Figure 2). In both experiments, untreated trees were drilled and Arborplugs installed so that stem injury could be simulated and any effects on tree responses evaluated against treatments. The size of lesion area produced around each point inoculation of O. minus was the primary response variable; standard meth- ods were employed to inoculate and measure lesions (Klepzig et al. 2005; Klepzig and Strom 2011). At each sample period, le- sions were measured approximately one month after inoculations were made at breast height (+/- 1 m). Inoculations required of the removal of a bark plug, 1.27 cm diameter, to expose the sap- wood face, which then received a single 0.5 cm plug of malt agar with O. minus. The O. minus was freshly isolated and cultured from living southern pine beetles collected on the Homochitto National Forest (Mississippi, U.S.). Once the O. minus was in place, the bark plug was replaced, securing the O. minus against the sapwood and promoting more natural conditions for fungal growth. For measurement of lesion size, bark was removed to expose the underlying lesion and the outer boundary of the le- sion traced onto a sheet of transparent film. Lesion area (square centimeters) was determined in the laboratory by tracing the out- lined area with a digital planimeter (Lasico model no. 1281-12). 2008 Experiment Three systemic fungicide products were applied to loblolly pines by stem-injection to assess for activity against O. minus: PHOSPHO-jet (45.8% Mono-and di-potassium salts of Phos- phorous Acid), Alamo (14.3% Propiconazole), and Arbotect 20-S (20% 2-(4-thiazolyl) benzimidazole). Treatments were applied on May 6–7, 2008 to loblolly pines near Williana, Louisiana, U.S. (N31°45’25.6”, W092°36’38.4”). This initial experiment was primarily a screening of the products, lead- ing to two dosages for each product and giving seven treat- ments, each replicated four times (four trees per treatment). PHOSPHO-jet was applied at 5 and 10 mL per 2.5 cm dbh, Alamo was applied at 10 and 20 mL per 2.5 cm dbh, and Ar- botect 20-S was applied at 3 and 6 mL per 2.5 cm dbh. These rates equate to 1 to 2× the label rate for PHOSPHO-jet; 1x the label and maximum therapeutic rate (of 2×) for Alamo; and 0.5 to 1× the Arbotect label rate. The lower rate for Ar- botect was selected due to concerns with possible phytotoxic- ity. Each was diluted with water (3, 4, and 33 volumes for Figure 2. Mean lesion areas (cm2 Figure 1. Mean lesion areas (cm2 ) resulting from single point in- oculations with the bluestaining fungus, Ophiostoma minus, into loblolly pines in central Louisiana. Trees were injected with one of three products (ARB = Arbotect 20-S, PHJ = PHOSPHO-jet, ALM = Alamo) at one of two doses (L = low, H = high) or left untreated. Lesions were determined from destructive sampling of bole tis- sue approximately 30 days following inoculation with O. minus on 2–4 sides of each tree. Injections with fungicide products were made on May 6–7, 2008. ) resulting from single point inoculations with the bluestaining fungus, Ophiostoma minus, into loblolly pines in central Louisiana in the second experiment. Trees were injected with one of two products (ARB = Arbotect 20-S, ALM = Alamo) either alone or with a mixture (2:1 Arbotect to Alamo [ARB2to1] or 3:1 Arbotect to Alamo [ARB3to1]) or untreat- ed (UNT). Lesions were determined from destructive sampling of bole tissue approximately 30 days following inoculation with O. minus on two sides of each tree. Injections with fungicide products were made on May 4–7, 2009. ©2011 International Society of Arboriculture
November 2011
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