Dissipation of fomesafen in fumigated, anaerobic soil disinfestation-treated, and organic-amended soil in Florida tomato production systems.

BACKGROUND: Fumigated, anaerobic soil disinfestation-treated (ASD), and organic-amended soil management strategies have been investigated as potential methyl bromide (MBr) alternatives for controlling diseases, nematodes, and weeds in soil. Nutsedge and broadleaf weed control using fomesafen has been reported to be comparable to MBr in normal cropping systems. There is no information on the fate of fomesafen used in combination with alternative practices. In this study, the fate of fomesafen in these alternative systems was measured by liquid chromatography-tandem mass spectrometry (LC/MS-MS) following extraction using a modified Quick Easy Cheap Effective Safe (QuEChERS) method. RESULTS: The reported half-life (DT50 ) values for fomesafen in the top 15 cm of soil were from 62.9 to 107.3 days. The DT50 values in organic-amended soil were higher than in ASD-treated soil in the top 15 cm. For all treatments, reductions in concentrations were positively correlated with lower redox potentials and organic matter content. Some leaching of fomesafen into the 16-30 cm zone was observed in all treatments. CONCLUSIONS: The DT50 values in this study were generally higher than those reported in previous studies performed at different locations. Due to increased losses of the herbicide and subsequent reduction in weed control, fomesafen is likely not to be suitable for effective weed control in systems using ASD techniques employing composted poultry litter and molasses. Integration of fomesafen using composted yard waste 1 (CYW1) and Soil Symphony Amendment (SSA) may result in acceptable weed control. Given that the soil was very sandy and the pH was higher than the pKa, fomesafen might leach deeper than 30 cm, particularly with the use of chemical soil fumigants (CSFs). © 2019 Society of Chemical Industry.

Survival of Inoculum of Phytophthora capsici in Soil Through Time Under Different Soil Treatments.

From September 2001 until August 2002 and from September 2002 until August 2003, inoculum of Phytophthora capsici consisting of mycelium and oospores was buried in soil under three different soil treatments: soil solarization, fumigation with methyl bromide and chloropicrin, and white-on-black plastic mulch without fumigation or solarization. The effect of these soil treatments on the population and survival of P. capsici was evaluated through time after 28, 63, 119, 175, 245, and 343 days. Three techniques were used for detection of the localized inoculum in soil: soil dilution plating (SDP), a modified soil dilution plating technique with an overlay assay to allow for extra incubation (mSDPO), and lemon leaf baiting of soil (LLB). No viable inoculum was detected from any soil samples from the fumigated plots regardless of the soil detection technique used. By the last sampling date, viable oospore inoculum was still detected in both soil solarization and nontreated soils, but only using mSDPO and LLB. Overall, the mSDPO assay was the most sensitive assay, followed by LLB. Using mSDPO, populations in the last sampling date were 32.9 CFU/g soil for the untreated plots and 14.7 CFU/g soil for the solarized plots. Survival of P. capsici for a year would indicate that oospores have the potential to survive from year to year, and possibly much longer, in Florida and other locations.