Persistence and Degradation Behaviour of Dimethoate in Grapes

Abstract

Through a field experiment, the dissipation pattern of dimethoate in grapes was evaluated during December 2020 - February 2021. Dimethoate 30%EC was sprayed twice at ten-days interval at recommended (X) dose (445 g a.i ha-1) and double the recommended (2x) dose (890 g a.i ha-1). The samples were collected from 0 (2hr), 1, 3, 5, 7, 10, 15 and 20 days or till degradation to below detectable level (BDL) and at harvest time. The residues were extracted by the modified QuEChERS method and analyzed by LCMS. The method performance was satisfactory in terms of SANTE guidelines and with good linearity (r2>0.99). The mean total dimethoate residue including omethoate was 1.047 and 2.168 mg kg-1 at x and 2x doses, respectively with half-lives of 5.47 and 5.59 days. The calculated Risk Quotient (RQ) at both x and 2x dose with Good Agricultural Practices (GAP) indicated that for dimethoate these are not safe for human health due to the intake of residue.

Risk assessment of Retithrips syriacus for the EU

“…Altogether, the three studies by Reddy and Rao (2002, 2003) and Reddy (2006) do no provide robust evidence of yield losses caused by R. syriacus on grapevine. The poor experimental design (factorial design with up to 8 replicates consisting of one single plant per treatment, with no control/untreated plants separating treatments) and result reporting in those papers present serious limitations and the damage attributed to R. syriacus cannot be disentangled from the two other grapevine pests present in the experimental site.…”

“…The main impacts reported in the literature are of qualitative nature with most of the records reporting only a description of the injuries on leaves following feeding or presence of faecal material. The quantitative evidence reporting yield loss attributed to R. syriacus is limited to three studies conducted in Andhra Pradesh (India) (Reddy, 2006; Reddy & Rao, 2002, 2003). Results reported on these papers are used to label this thrips as responsible for significant losses or even ‘devastating’ in grapevine (AGDA, 2016; DROPSA, 2016).…”

“…All the literature noted above is mainly descriptive of the injuries caused by R. syriacus during its feeding activity, but without reporting actual impacts on yield or quality in a qualitative or quantitative way. The only studies available which report data on yield losses associated with R. syriacus are (Reddy & Rao, 2002, 2003) and (Reddy, 2006) from India, which are described and scrutinised below.…”

“…In Reddy and Rao (2003), the flea beetle was controlled using pesticide treatments, but it is unclear whether this control was fully effective. Moreover, pod borer infestation is not mentioned in Reddy and Rao (2003) while this pest was present in Bolaram during the same years according to Reddy and Rao (2002).…”

“…According to Reddy and Rao (2003), the thrips population ranged from 22.58 individuals per 10 canes to 62.13 individuals per 10 canes in untreated plots. These numbers correspond to about three to six thrips individuals per (untreated) cane, which seems to be very low as R. syriacus is known to live in clusters including many individuals (usually around 50 individuals per grape leaf according to Dr. Eleunorah Allsopp, personal communication).…”