Arboriculture & Urban Forestry 43(4): July 2017 named cultivar, as they had been grown from non-certified seed. However, their characteristics were most closely associated with the Malayan Dwarf cultivar. These palms are growing in a uni- form Margate fine sand soil and had not been subjected to any pesticide treatments prior to this experiment. Since 2005, the palms had been fertil- ized four times each year with 3.15 kg per palm per application of a controlled-released fertilizer (Lesco, Cleveland, Ohio, U.S.), 8N-0.9P-10K-4Mg plus micronutrients (2.0% Mn; 0.15% B, Fe, and Zn; 0.05% Cu). All palms had trunks at least 5.5 m high with at least 15 leaves. The palms were 4 m apart in all directions. Mean diameter at breast height (dbh) was 25 cm (range of 20 to 32 cm). Since dbh in palms does not correlate with canopy size or leaf number, and the goal was to determine if fungicides move into the leaves, it was decid- ed to use the mean dbh (25 cm) for calculating fungicide application rates. Leaves used for sam- pling were numbered by starting with the newest growth at the time the fungicides were applied. The emerging spear leaf was designated leaf 0, the next-oldest leaf as leaf 1, and so on down through the canopy to the oldest leaf. Leaves that emerged aſter the start of the experiment were labeled with negative numbers (-1, -2, etc.) (see Figure 1). The first experiment was initiated in August 2010. The second experiment used the same palms but was not initiated until July 2012 to allow for a completely new canopy of leaves to develop, which would also ensure there was no fungicide residual. Fungicides and Application Methods 2010 Four fungicides were evaluated in 2010: 1) thia- bendazole at 52.2 g a.i. per palm (Arbotect® 20-S; 220 g a.i. per liter; Syngenta Crop Protection, Inc., Greensboro, North Carolina, U.S.); 2) propiconazole at 15.6 g a.i. per palm (Alamo®, 156 g a.i. per liter; Syngenta Crop Protection, Inc., Greensboro, North Carolina, U.S.); 3) tebuconazole at 5 g a.i. per palm (Tebuject™ 16; 168 g a.i. per liter; Mauget, Inc., Arca- dia, California, U.S.); 4) thiophanate methyl at 21.3 g a.i. per palm (3336®F; 479 g a.i. per liter; Cleary Chemical Corporation, Dayton, New Jersey, U.S.). There were four palms per fungicide treatment, and two palms for the untreated control treatment. Treatments were randomly assigned to the palms. 135 Figure 1. Location of palm tissues sampled for fungicide bioassay. Figure reprinted with permission of M.L. Elliott and HortScience. To repeat and expand on the initial study con- ducted with thiabendazole (Elliott and Broschat 2012), thiabendazole, propiconazole, and tebucon- azole fungicides were applied passively using pine tree infusers provided by Rainbow Treecare™ Sci- entific Advancements (Minneapolis, Minnesota, U.S.). The fungicides were not diluted prior to appli- cation. Two holes on opposite sides of the trunk at breast height were drilled 8.5 cm deep using a ~0.2 cm drill bit. The infuser nozzle was tapped into the trunk with a rubber mallet to a 2.5 cm depth, and the capped tube attached to the nozzle was tied upright to the trunk with flagging tape. Since each infuser only held 40 ml, the liquid was replen- ished in the infusers as the liquid was taken up by the palm. Infusers were removed aſter 30 hours. Thiophanate methyl was applied as a root drench. To prevent turfgrass and weed roots from intercepting the fungicide, glyphosate was sprayed on a 3.3 m2 area, with the palm in the center, two weeks prior to the drench. The fun- gicide was mixed with water, and each palm received 36 L of the fungicide mix applied with ©2017 International Society of Arboriculture
July 2017
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