Arboriculture & Urban Forestry 43(4): July 2017 Between the 2010 and 2012 experiments, the label for Alamo (propiconazole) changed. The amount of material that could be used for a single dose was doubled, probably to increase the persistence of propiconazole in red bay (Persea borbonia) and avo- cado (Persea americana) (Mayfield et al. 2008; Ploetz et al. 2011). Research regarding laurel wilt disease, caused by Raffaelea lauricola, affecting members of the Lauraceae in southeastern U.S., had suggested that the persistence of propiconazole, when using the 2010 labeled rate, began to decline 4.5 months aſter root-flare injections (Mayfield et al. 2008). For both propiconazole and thiabendazole, evi- dence of movement into new growth is demon- strated by the detection of the fungicides in the rachises of leaves labeled with a negative number; in other words, leaves that had not yet emerged at the time of the fungicide application. For exam- ple, in 2012, propiconazole was detected in the basal and distal rachis of leaf -1 of all four repli- cate palms. This leaf number was sampled 13 weeks aſter the fungicide was injected. Similar results were obtained for thiabendazole in both 2010 and 2012. However, what is also evident is the decrease in propiconazole and thiabendazole in leaves in the palm canopy over time. With thiabendazole, this was evident in the distal rachis tissue at the 16-week post-application sampling in 2010, and even earlier in 2012 for three of the four replicate palms. For propiconazole in 2012, no or mini- mal material was detected in most leaf samples at 18 weeks. In both years, neither propicon- azole or thiabendazole was detected in any leaf by 28 weeks aſter treatment (data not shown). Research results with thiabendazole, includ- ing the current study as well as a previous study (Elliott and Broschat 2010), are fairly consistent with results obtained for thiabendazole used in elm trees, as summarized by Stennes (2000). First, a bioassay technique for detection of thiabenda- zole in plant tissue is feasible when using twig (hardwood) or rachis (palm) tissue. Second, the fungicide was evenly distributed in the canopy. Third, the fungicide could be detected in tissue not yet developed (hardwood) or fully developed (palm) at the time of the injection. The primary difference is the persistence of thiabendazole, which appears to be as long as 12 months in elm trees but less than 5 months for coconut palms. 141 Propiconazole persistence in coconut palms was also less than five months. Results with per- sistence of propiconazole in trunk vascular tis- sue of hardwood trees have been mixed. One study with red oak (Quercus rubra) demonstrated propiconazole was detected in trunk tissue 12 months aſter injection (Osterbauer and French 1992), but another study with red oak reported in Blaedow et al. (2010) indicated it was not. In general, fungicide persistence seems longer in hardwood trees than in palms (Stennes and French 1987; Osterbauer and French 1992; May- field et al. 2008; Blaedow et al. 2010). However, the fungicide persistence results in palms are not greatly different from the results obtained with oxytetracycline HCl injections (McCoy 1976). Methods for consistently inoculating palms with pathogens and observing disease development in mature, tall palms in field nurseries have not been successful. Therefore, it is necessary to con- duct research in large landscapes where diseases, such as Fusarium wilt, petiole blight, and rachis blight are naturally occurring. The results from this research will help predict which fungicides are likely to be effective for palm disease management. Acknowledgments. This work was sup- ported, in part, by a grant from the TREE Fund (John Z. Duling grant number 04-JD- 10) and by the USDA National Institute of Food and Agriculture Hatch Project 228670. We thank Elizabeth Des Jardin for her technical support. LITERATURE CITED Adaskaveg, J.E., H. Förster, L. Wade, D.F. Thompson, and J.H. Connell. 1999. Efficacy of sodium tetrathiocarbonate and propi- conazole in managing Armillaria root rot of almond on peach rootstock. Plant Disease 83:240–246. Ali, A.D., and D. Caldwell. 2010. Royal palm bug Xylastodoris luteolus (Hemiptera: Thaumastocoridae) control with soil applied systemics. Florida Entomologist 93:294–297. Blaedow, R.A., J. Juzwik, and B. Barber. 2010. Propiconazole distri- bution and effects on Ceratocystis fagacearum survival in roots of treated red oaks. Phytopathology 100:979–985. Dal Maso, E., J. Cocking, and L. Montecchio. 2014. Efficacy tests on commercial fungicides against ash dieback in vitro and by trunk injection. Urban Forestry & Urban Greening 13:697–703. DeFranqueville, H., and J.L. Renard. 1989. Effectiveness of Fosetyl- Al in controlling Phytophthora of coconut. Application methods. Oleagineux 44:351–358. Delp, C.J. 1995. Benzimidazole and related fungicides. pp. 291– 303. In: H. Lyr (Ed.). Modern Selective Fungicides: Properties, Applications, and Mechanisms of Action. Gustav Fischer Ver- lag, New York, New York, U.S. ©2017 International Society of Arboriculture
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