140 Elliott and Broschat: Uptake, Movement, and Persistence of Fungicides in Mature Coconut Palms bamates, with thiophanate methyl in the thio- phanates chemical group and thiabendazole in the benzimidazole chemical group (Delp 1995; FRAC 2016). Propiconazole and tebuconazole are demethylation inhibitor fungicides and are in the triazole chemical group (Kuck et al. 1995; FRAC 2016). All fungicides used in the current study were xylem-mobile systemic products. In theory, such products, when taken up by the root system, will move throughout the plant via the xylem. All four fungicides are formulated differently. Arbotect 20-S is a soluble liquid concentrate of thia- bendazole hypophosphate; Alamo is a microencap- sulated emulsifiable concentrate of propiconazole; Tebuject 16 is an emulsifiable concentrate of tebu- conazole; 3336F is a flowable concentrate of thio- phanate methyl. While the first three products have been formulated for trunk and root-flare injection of trees, thiophanate methyl has not, probably due to the fact it does not form a solution in water. It was included in the study because it is a standard fun- gicide used on palms in the Florida landscape, not for root disease control but for canopy disease con- trol, even though there are no studies regarding its effectiveness for disease control in mature palms. While there was considerable variability in Peni- cillium inhibition by individual rachis pieces, the overall inhibition was relatively uniform in the leaf canopy for the first three sampling dates for both thia- bendazole and propiconazole in both years. The Pen- icillium inhibition assay provided a uniform method of detecting the fungicides. In other words, different chemical analytical assays were not required for the detection of each fungicide. The QuEChERS method for homogenizing samples prior to analysis with ultra-high-performance liquid chromatography- tandem mass spectrometry may solve this prob- lem (Ferreira et al. 2015). However, this method is time-consuming, requires dry ice for crush- ing, and expensive equipment and consumables. In this study, thiophanate methyl, propicon- azole, and thiabendazole were not detected in the palm canopy when applied as root drenches. The inability to detect thiophanate methyl in the canopy was not surprising. A study conducted on coco- nut in Brazil injected technical material of both thiabendazole and thiophanate methyl. Aſter 45 hours, thiabendazole was detected but not thio- phanate methyl (Ferreira et al. 2015). While the ©2017 International Society of Arboriculture authors attributed this to the fact that thiophan- ate methyl is metabolized to carbendazim (as is benomyl), they did not consider the fact that thiophanate methyl is more stable than benomyl and would not have been broken down to carben- dazim in less than 48 hours (Delp 1995). Plus, the level of carbendazim detected was not doubled, as would be expected if thiophanate methyl was being quickly metabolized to carbendazim as postulated. The effectiveness of any of the benzimidazoles as a soil application has been poor, as the compounds are tightly adsorbed to soil colloids and organic matter (Delp 1995). Practical disease control has been obtained by application to potting substrates for container-grown plants, incorporation into plant beds, or in-furrow applications (Delp 1995). Mobility in soil is expected to be slight to none for propiconazole, slight for thiabendazole, and mod- erate for thiophanate methyl (NCBI 2015; NCBI 2016a; NCBI 2016b). This slight-to-no mobility in soil may explain why propiconazole and thia- bendazole are not labeled for soil applications. In the 2010 study, tebuconazole was not detected in the palm canopy. This was likely due to this for- mulation’s incompatibility with compounds in the vascular bundles. Very little of the material was passively taken up by the palms due to the clog- ging of the nozzles. Attempts to inject the tebu- conazole with pressure were also unsuccessful. Although this product has been used in hardwood trees, it may be necessary to develop a formula- tion that is more water compatible for injection into palms, which contain considerably more water than hardwood trees due to their vascular structure. While thiabendazole and propiconazole were not detected in the palm canopy when applied as root drenches, they were detected in the palm canopy when passively infused or injected under pressure. Propiconazole was only detected in two of four replicate palms in the 2010 study, but was detected in all four replicate palms in the 2012 study. Although the method of appli- cation changed from 2010 (infusion) to 2012 (pressurized injection), it is more likely that the increased detection in 2012 was due to the increased amount of propiconazole used. This is presumed because the method of application did not affect thiabendazole detection, where the same amount of chemical was used in both years.
July 2017
| Title Name |
Pages |
Delete |
Url |
| Empty |
Search Text Block
Page #page_num
#doc_title
Hi $receivername|$receiveremail,
$sendername|$senderemail wrote these comments for you:
$message
$sendername|$senderemail would like for you to view the following digital edition.
Please click on the page below to be directed to the digital edition:
$thumbnail$pagenum
$link$pagenum
Your form submission was a success. You will be contacted by Washington Gas with follow-up information regarding your request.
This process might take longer please wait
