Arboriculture & Urban Forestry 36(6): November 2010 the trunk about one-third of its diameter and was injected using the same techniques as treatments 3 and 4. Arborplugs are poly- propylene inserts with a membrane sealing the small-diameter injection port in the center. They are tapped into holes in the trunk such that the membrane is within the central cylinder of the palm trunk containing the vascular bundles. The Quick-jet microinjec- tor is a repeating syringe with a needle that penetrates the Arbor- plug membrane and injects a measured volume of solution into the trunk or petiole. All treatments were applied April 7–8, 2009. Prior to treatment, leaf samples consisting of two central leaf- lets from the youngest fully-expanded leaf (leaf #1) on each tree were harvested for baseline Mn determinations. Similar samples were collected from the current youngest fully-expanded leaves at 1, 3, and 6 months following treatment. Leaf samples were dried at 60°C, ground, and digested using a nitric acid-hydrogen peroxide method (United States EPA 1996). Digested samples were analyzed for Mn concentrations using atomic absorp- tion spectrometry. In order to eliminate intra-plant variation in Mn content, initial Mn concentration data from each tree were subtracted from the 1, 3, and 6-month leaf Mn concentrations. Analysis of variance, with mean separation by the Waller- Duncan k-ratio method (SAS Inst., Cary, NC, U.S.), was used to compare changes in Mn concentrations among treatments. RESULTS AND DISCUSSION Injection of the trunks of coconut palms was relatively sim- ple and leakage was minimal if the Arborplug was properly seated. Injection into petioles was more difficult and the lim- ited capacity of the petiole to absorb injected solutions lim- ited the volumes that could be injected to about 2 mL per hole. In two of the trunk-injected palms, more than 25 mL of solution were unable to be injected into a single hole. Analysis of baseline Mn concentrations showed that all palms were above the 40 ppm threshold for Mn sufficiency (Elliott et al. 2004). However, there was a wide range in concentrations among replicate trees within each treatment. For that reason, the concentrations at 1, 3, and 6 months were subtracted from the initial concentrations to show changes in concentrations over time in response to the various treatments. Treatment 5 (trunk injection) went from the lowest concentration at month 0 to the highest at month 1, and showed an increase in Mn of about 102 ppm (Table 1). Other treatments showed little or no increase in Mn concentrations. At month 3, trunk-injected palms (treat- ment 5) still had Mn concentrations 113 ppm higher than before treatment while the other four treatments showed net losses in Mn in their foliage. After 6 months, treatment 5 still had high- er Mn concentrations than before treatment, while the other 273 four treatments showed significant drops in Mn concentrations. The drop in most Mn concentrations over time was most likely due to a dilution effect caused by an increased growth rate dur- ing the warm rainy summer months. Broschat (1991) showed a similar drop in Mn concentrations in leaves of untreated pygmy date palms (Phoenix roebelenii) sampled in July, compared to cooler and drier months of February through May at a nearby site. Thus, it was important that changes in Mn concentra- tions were presented, as opposed to the actual concentrations. These data suggest petiole injection of older leaves is not fective in increasing Mn concentrations in the foliage of pygmy date palms growing in a similar soil (Broschat 1991) CONCLUSIONS rial, and lasted 6 months. However, because this method results in permanent trunk wounds that could provide entry sites for the le- thal trunk pathogen Thielaviopsis paradoxa, this method should not be used on relatively young specimens where foliar sprays are possible and where drilling will necessarily be done into trunk tis- sue that has not had sufficient time to thoroughly lignify (Tomlin- son 1990). Thielaviopsis paradoxa requires a wound for infection Petiole injection of Mn is an ineffective means of increasing Mn in leaf #1 and does not justify the extra effort required to treat palms. On the other hand, in this experiment, trunk injection was more effective than soil application of MnSO4 Table 1. Actual and changes in Mn concentrations (from month 0) in leaf 1 of coconut palms that were treated with manganese sulfate via soil application, petiole injection, or trunk injection. Means with different letters following are statistically different at the P = 0.05 level based on the Waller-Duncan k-ratio method. (n = 10) Treatment 1: Control (no Mn) 2: Soil application 3: Petiole injections (4) 4: Petiole injection (1) 5: Trunk injection P-value 128.6 143.1 112.6 89.8 0.088 Month 0 Month 1 118.5 Actual Mn concentration (ppm) Month 3 89.8 b 116.4 b 145.7 ab 145.9 ab 110.5 b 191.8 a 0.0254 97.5 b 125.6 b 84.9 b 203.2 a 0.0002 Month 6 69.6 b 73.4 b 86.6 ab 63.6 b 113.3 a 0.033 Month 1 2.1 b 17.2 b 2.8 b -2.1 b 101.9 a <0.0001 Change in Mn concentration (ppm) Month 3 -28.7 b -31.1 b -17.5 b -27.7 b 113.4 a <0.0001 Month 6 -48.9 b -53.2 b -56.5 b -49.0 b 23.5 a <0.0001 ©2010 International Society of Arboriculture , used much less mate- an effective method of increasing Mn in the newest leaf (leaf #1) of a palm, the site where Mn deficiency develops and the leaf that was sampled in this study. Although injections of the antibiotic OTC into coconut palm petioles provided sufficient chemical in all leaves of the canopy to suppress the lethal yel- lowing phytoplasma, the concentrations of OTC in noninjected leaves averaged only about one-tenth of that found in injected leaves (McCoy 1977). OTC is known to be phloem-mobile, while Mn is considered to be only partially so (Bukovac and Wittwer 1957). Broschat (1997) found that Mn was mobilized from older leaves to leaf #2 within the canopies of coconut palms, but not to leaf #1. Thus, even if petiole injection had increased Mn concentrations in leaf 2, this would have no ef- fect on the incidence or severity of Mn deficiency, which de- velops in the expanding leaf 0 and the newly expanded leaf 1. In this experiment, soil applications provided a minimal increase in Mn concentrations at 1 month, but not thereaf- ter, suggesting that applied Mn was quickly oxidized by Mn- oxidizing bacteria (Sparrow and Uren 1987). Since the pH of this soil was not particularly high (6.1), precipitation of Mn by high soil pH (Lindsay 1972) was probably less of a fac- tor in this study. Soil applications of MnSO4 were highly ef-
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