Mobility of Oxathiapiprolin and Mefenoxam in Citrus Seedlings After Root Application and Implications for Managing Phytophthora Root Rot

Abstract

Oxathiapiprolin is highly effective in the management of Phytophthora root rot of citrus, however, its uptake into plants after soil application is not known. This was investigated and compared with mefenoxam using potted citrus seedlings sampled 7, 10, 13, and 16 days after soil treatments. Bioassays and liquid chromatography-tandem mass spectroscopy (HPLC-MS/MS) were used to quantify fungicide amounts in plant extracts. Distinct inhibition zones of mycelial growth of Phytophthora citrophthora were observed in bioassays when root, stem, or leaf extracts were added to filter paper disks on agar plates. Based on the two quantification methods, concentrations of both fungicides in the three tissue types and at all sampling times were above the mean EC50 values of the baseline sensitivities. Relative concentrations at the four sampling times sometimes varied between the two methods, but for both methods, concentrations of oxathiapiprolin were significantly higher in roots and leaves as compared with stems 10 days after treatment and statistically similar in the three tissues after 7 days. For mefenoxam, concentrations significantly increased in roots between 7 and 16 days after treatment and were significantly the highest in roots as compared with stems or leaves 16 days after treatment. Regressions of oxathiapiprolin and mefenoxam concentrations using HPLC-MS/MS on those calculated from bioassay standard curves indicated that the bioassays over-estimated fungicide amounts in the extracts. The bioassay, however, can be considered a comparable alternative option to costly residue analyses in fungicide mobility studies in plants. Uptake of oxathiapiprolin at sufficient, but low concentrations into plant roots provides an explanation for its long-lasting high activity in the management of Phytophthora root rot.

Metalaxyl-resistant mutant strains of Phytophthora boehmeriae are as aggressive and fit as their metalaxyl-sensitive wild-type parents

“…Thereby, there would be a high risk of development of metalaxyl resistance in populations of P. boehmeriae in the field, when metalaxyl was long and continuously applied for the control of the diseases caused by P. boehmeriae, which could lead to the defeat in controlling plant blight with metalaxyl. In addition, it must be noted that mefenoxam, metalaxyl-M, is the more recent isomer of metalaxyl, contains a much higher concentration of the active enantiomer of the original metalaxyl, and is therefore effective in the field (Parra and Ristaino 2001;Rubin et al 2008;Hu and Li 2014;Lookabaugh et al 2018;Gray et al 2020;Gonzalez-Tobon et al 2020;Siegenthaler and Hansen 2021).…”

“…For this reason, Fangxin Chen and Yongxia Qi contributed equally to this work. and due to selection pressure brought by a long use of the fungicide, developments of resistance to metalaxyl among members of the oomycetes, including the genus Phytophthora, have appeared in many countries (Café-Filho and Ristaino 2008;Gisi and Sierotzki 2008;Hu et al 2008;Pérez et al 2009;Lookabaugh et al 2018;Gray et al 2020;Gonzalez-Tobon et al 2022).…”

Enantioselective Residue Dissipation of Oxathiapiprolin during Tea Growing, Processing, and Brewing

“…8 Gray et al investigated the comparative mobility and residues of oxathiapiprolin in citrus seedlings after soil applications according to the current standards accepted by the United States Environmental Protection Agency; the results indicated that oxathiapiprolin had potential to long residual activity and persistence in citrus crops. 9 Wang et al used QuEChERS combined HPLC−MS/MS to determine the residue of oxathiapiprolin in cucumber, and a dietary risk assessment was carried out to demonstrate a low health risk from oxathiapiprolin. 10 Although there were many reports and literature studies on the degradation of oxathiapiprolin in different environments and agro-products, most of them only focused on the residues of oxathiapiprolin racemate and ignored its enantioselectivity.…”

“…Feng et al used the field data and dynamiCROP modeling to analyze the distribution, uptake, and translocation mechanisms of oxathiapiprolin in leafy vegetables (Chinese cabbage and lettuce) and herbaceous vegetables (cucumber and tomato) and evaluated the potential human exposure to its residues from consumption of these agro-products; the field trials indicated that the final human intake of oxathiapiprolin ranges between 10 –4 and 10 –3 kg intake /kg applied . Gray et al investigated the comparative mobility and residues of oxathiapiprolin in citrus seedlings after soil applications according to the current standards accepted by the United States Environmental Protection Agency; the results indicated that oxathiapiprolin had potential to long residual activity and persistence in citrus crops . Wang et al used QuEChERS combined HPLC–MS/MS to determine the residue of oxathiapiprolin in cucumber, and a dietary risk assessment was carried out to demonstrate a low health risk from oxathiapiprolin …”

Assessing the effectiveness of oxathiapiprolin towardsPhytophthora agathidicida, the causal agent of kauri dieback disease

“…It can be applied via foliar sprays, soil applications (e.g. in-furrow) or soil drenches and it is efficiently translocated throughout plant tissues in a variety of horticultural species (Cohen 2015(Cohen , 2020Qu et al 2016b), including perennial tree crops (Gray et al 2020). In addition, oxathiapiprolin has low phytotoxic effects in host tissue.…”