136 a bucket to a 2.3 m2 Elliott and Broschat: Uptake, Movement, and Persistence of Fungicides in Mature Coconut Palms area, with the palm in the center. The ground was moist, as it had rained the night before the root-drench application. 2012 Based on knowledge gained in the 2010 experi- ment, only thiabendazole and propiconazole were evaluated in 2012, as thiophanate methyl was not detected in the leaf tissue in 2010 and the tebuconazole formulation was not com- patible with infusion or injection into palms. The thiabendazole rate (52.2 g a.i. per palm) and formulation was the same as in 2010, but the propiconazole rate was doubled to 31.2 g a.i. per palm, using the same formulation. The fungicides were applied using two methods, and the applications were completed by noon. For trunk uptake, instead of passive uptake of the fungicides using the pine tree infuser system, palms were injected with the Tree I.V. Micro Infusion® system (Arborjet, Inc., Woburn, Massachusetts, U.S.). One hole, located ~1 m from the soil line, was drilled 5 cm deep into the trunk using ~0.7 cm drill bit. A #3 Arbor- plug® was tapped into the hole, a bottle contain- ing the fungicide was attached per instructions, and the system was pressurized to 207 kPa using the pump provided. All fungicides were taken up by the palms within four hours. A preliminary test demonstrated that the thia- bendazole and propiconazole did not have to be diluted with water in order to be efficiently taken up by the palm via pressurized injection. Each fungicide was also 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 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 a bucket to a 2.3 m2 center. The ground was moist, as it had rained the night before the root-drench application. There were four palms per fungicide x application treatment, and two palms for the untreated control treatment. Treat- ments were randomly assigned to the palms. Bioassay for Fungicide Detection A bioassay method was used to detect the fungi- cides in the leaf tissue sampled (Elliott and Bros- chat 2012). The fungus used was a Penicillium sp. (PLM-445), which is sensitive to all four fungi- cides. Spore suspensions were prepared in sterile deionized water, diluted to 104 spores per ml and added to sterile water agar. A thin layer of this agar-spore suspension was spread on the surface of 1/5 strength potato dextrose agar amended with 300 µg/ml streptomycin sulfate to inhibit bacterial growth. The fungal-seeded media was used immediately. Aſter leaf tissue, obtained as described herein, or fungicide-saturated, paper discs were placed on the media, plates were incu- bated at 25°C in the dark. Aſter 40 hours incuba- tion, zones of fungal inhibition were measured in two directions and the average was recorded. Standard inhibition curves were developed using sterile filter paper discs (6-mm diam- eter) saturated with a range of known con- centrations of each fungicide. After drying, discs were placed on fungal-seeded media. Regression analysis was performed to obtain the equation that best fit the data for the standards at each sampling date. This equa- tion was then used to calculate the amount of fungicide detected in the palm tissue. For sampling the rachis tissue, two 10-cm seg- ments were obtained from each leaf: i) basal por- tion of the rachis (BR), located about 45 cm from beginning of the rachis, and ii) distal portion of the rachis (DR), located about 45 cm from leaf tip (see Figure 1). The epidermis of each seg- ment was removed and a cross section selected and cut into 5-mm by 5-mm pieces of ~2-mm thickness. There were four sections from each of the two segments placed on each of the fungal- seeded media in 2010, and six sections from each of the two segments in 2012. Note that sampling the rachis is destructive sampling, since the leaf is removed from the canopy. On each sample date, one of the oldest (=lower) leaves, a mid-canopy leaf (=middle), and the youngest, fully expanded leaf (=upper) was sampled from each palm. The 2010 experiment was initiated on 16 August. Leaf samples were obtained on 13 Sep- ©2017 International Society of Arboriculture
July 2017
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