Residual analysis of chitosan-based agronanofungicides as a sustainable alternative in oil palm disease management

The nanoformulations of pesticides have shown great interest from many parties due to their slow release capability and site-specific delivery. Hence, in this work, a new nanoformulation of a fungicide, namely chitosan-hexaconazole nanoparticles with a mean diameter size of 18 nm was subjected to the residual analysis on oil palm tissue, leaf and palm oil (crude palm oil and crude palm kernel oil) using a quick, easy, cheap, effective, rugged and safe (QuEChERS) method coupled with the gas chromatography–micro electron capture detector (GC–µECD). The chitosan-hexaconazole nanoparticles were applied using the trunk injection method at 4.5 g a.i./palm (standard single dose) and 9.0 g a.i./palm (double dose). The fungicide residue was analyzed at 0 (6 h after application), 1, 3, 7, 14, 30, 60, 90, and 120 days after treatment. The palm oil matrices; the crude palm oil (CPO) and crude palm kernel oil (CPKO) were found to be residue-free. However, it was observed that high accumulation of the fungicide in the stem tissue and leaf after the treatment using the chitosan-hexaconazole nanoparticles, which is good for better bioavailability for the treatment of the fungi, Ganoderma boninense. The dissipation kinetic at double dose treatment in the tissue and leaf was found to govern by the second-order kinetic with half-lives (t1/2) of 383 and 515 days, respectively.

The Effect of Exogenous Melatonin in the Regulation of the Degradation of Residual Fungicide in Tomato

Fungicides are widely used to control pathogen in modern agriculture. In particular, in the process of vegetable production, the use of fungicides could control a variety of diseases to increase crop yield. However, it is common that excessive and unsuitable application of pesticide cause serious pesticide residue in vegetables, which leads to problems of food safety and environment pollution. Therefore, it should not be ignored to reduce fungicide residue in vegetable. In order to confirm the effect of exogenous melatonin on degradation of residual fungicide in plant and explore the mechanism of regulation, Chlorothalonil was taken as experiment material in the present study, and exogenous melatonin was applied as pretreatment to investigate the mechanism of the degradation of residual Chlorothalonil in tomato. It is demonstrated that exogenous melatonin pretreatment could promote the degradation and metabolism of CHT residue in tomato plants by inducing the redox signal, improving the antioxidant system, enhancing antioxidant enzymes and increasing the ratio of GSH/GSSG to scavenge reactive oxygen species. And the activity of GST and GR enzymes were also enhanced to conduct detoxification, which result in a pronounced decrease in the residue of CHT in tomato.

Refinement of Peach Cover Spray Programs for Management of Brown Rot at Harvest

Peach cover spray applications of the protectant fungicide captan were previously shown to significantly reduce brown rot caused by Monilinia fructicola during the preharvest fruit ripening periods in the 2012 through 2015 growing seasons. The protectants sulfur, ziram, and thiram failed to yield this benefit. Percentage disease control with captan ranged from 50 to 69%. Results of a bioassay indicated that the mechanism for this control was the creation of an effective, persistent fungicide residue on the fruit surface. Given these findings, the current 2017 to 2018 study was initiated to further refine the cover spray program. Cover spray applications of captan were made at lower rates and fewer timings with the goal of minimizing fungicide usage while maintaining control. High concentrations of the protectants sulfur and ziram were also examined in cover spray programs to determine whether greater concentrations could improve control. Results of the captan treatments from both years showed that the concentration could be reduced 17%, from 3.36 to 2.80 kg/ha active ingredient, without a significant increase in rot at harvest. Disease control at this medium rate was 69% in 2017 and 51% in 2018. The late season timing treatment, which consisted of the final two cover sprays at fifth and sixth cover, significantly reduced brown rot at harvest and provided control equivalent to the full cover spray program consisting of seven applications. Thus, a buildup of residue from many cover sprays is not needed to achieve control. As hypothesized, the midseason treatments, which consisted of two sprays at third and fourth cover, did not provide control of brown rot at harvest. The bioassay confirmed that insufficient residue remained on fruit for adequate control. However, the early season treatment, which consisted of sprays at shuck split, first cover, and second cover, provided 40% control, even though the bioassay showed that an effective residue was not present during the preharvest period. Brown rot management for this treatment was probably caused by inhibition of quiescent or latent infections on young green fruit. If confirmed, this novel finding indicates that high levels of latent infections are possible in eastern U.S. peach growing regions. Finally, higher rates of sulfur and ziram cover sprays were still ineffective for providing brown rot control at harvest. Comparison of half maximal effective concentration values calculated from the dose–response models confirmed that the sulfur and ziram intrinsic efficacies were too low for adequate control, even at the highest registered rates. These findings demonstrated that late season captan cover sprays can contribute significantly to control of brown rot at harvest, thereby augmenting the efficacy of preharvest fungicide programs. The year-to-year consistency of control should also be improved because heavy rainfall during the preharvest period did not reduce control by the captan residue. Furthermore, any reduction of the M. fructicola population by the captan cover sprays should reduce selection pressure against the site-specific fungicides commonly used during the preharvest period. The development of resistance to captan, a multisite protectant fungicide, is not likely, so this resistance management strategy should be sustainable.

Contribution of Mid-Season Cover Sprays to Management of Peach Brown Rot at Harvest

Four protectant fungicides applied as midseason cover sprays were quantitatively assessed for their ability to reduce brown rot caused by Monilinia fructicola during the preharvest fruit ripening periods in the 2012 through 2015 growing seasons. No fungicides were applied during bloom or during the preharvest period. Treatment programs consisted of captan, sulfur, ziram, and thiram applications beginning at early shuck-split stage and ending with the final cover spray at 23 to 26 days before harvest. The incidence of brown rot at harvest was determined by examining 41 to 91 fruit for symptoms of rot on each of four replicate trees for each treatment. The incidence of sporulating blossom blight cankers was assessed during the preharvest period at 8, 15, and 22 days after the final cover spray. An in vivo bioassay was also conducted at 7, 14, and 21 days after the final cover spray to ascertain the level of fungicide residue during the preharvest period. The bioassay uses conidia germination as a quantitative indicator of effective residue. Results of the harvest assessment showed that captan cover sprays significantly reduced brown rot incidence in all years of the study. Furthermore, results of the bioassay demonstrated that fungicide residue was the mechanism by which this control occurred. None of the other fungicide cover spray programs contributed significantly to brown rot control at harvest in any year, and bioassay results showed insufficient residue to inhibit conidial germination. Antisporulant activity against blossom blight cankers was not observed for any fungicide program, indicating that reducing inoculum production from this source was not a mechanism for brown rot control. The captan and sulfur programs provided very good control of peach scab incidence and severity, caused by Fusicladium carpophilum, while the ziram and thiram programs failed to control this disease. These findings demonstrated that captan cover sprays can contribute significantly to control of brown rot at harvest, thereby augmenting the efficacy and consistency of management by preharvest fungicide programs. Furthermore, any reduction of the M. fructicola population by the captan cover sprays should reduce selection pressure against the site-specific fungicides commonly used during the preharvest period, thereby prolonging their useful life for brown rot control.

Comparison of SPE/d-SPE and QuEChERS-Based Extraction Procedures in Terms of Fungicide Residue Analysis in Wine Samples by HPLC–DAD and LC-QqQ-MS

Two different extraction and clean-up protocols, based on either the SPE/dispersive SPE (d-SPE) or the quick, easy, cheap, effective, rugged, and safe approach, were optimized and compared for determination of six selected fungicides (benalaxyl, metalaxyl, triadimenol, tebuconazole, diniconazole, and epoxiconazole) in wine samples. The pilot study was performed by applying HPLC with diode-array detection, and optimized procedures were easily transferred to the LC triple-quadrupole MS system. Both extraction procedures presented good performance for all the analytes, with recoveries in the range of 70–132% and SDs ≤20%. The d-SPE clean-up step included in both procedures allows obtaining colorless extracts with the majority of coextracted matrix compounds removed. LC with electrospray ionization and tandem MS operating in the multiple reaction monitoring mode provide high sensitivity and selectivity for trace analysis. Both developed procedures were evaluated in terms of commercial wine sample analysis. In three wine samples, metalaxyl and tebuconazole residues were detected at concentrations from 0.14 to 30.7 ng/mL. Both approaches showed satisfactory feasibility for fungicide residue analysis in wine samples.

An In Vivo Bioassay for Estimating Fungicide Residues on Peach Fruit

Recent fungicide efficacy studies indicated that brown rot fruit rot at harvest, caused by Monilinia fructicola, was being controlled by residual activity from protectant fungicides applied during the time between bloom and the preharvest fruit ripening period. To determine the extent of this residue, a simple in vivo bioassay was developed by assaying M. fructicola spore germination directly on sampled fruit. A 1.5-cm section of clear flexible tubing was placed upright on harvested fruit to create a small incubation well. After the tubing–fruit interface was sealed using silicon grease, a suspension of M. fructicola conidia was pipetted into the well. The spores were suspended in a buffer-substrate medium consisting of 0.025 M potassium phosphate, 0.1% sucrose, and 0.1% yeast extract. A rubber stopper with an aeration hole was inserted into the well’s top and the fruit was placed in an incubator at 25°C. Results of a time-course study indicated that the optimal conidial incubation time was 6 h. Bioassay sensitivity was evaluated by examining test results from varying concentrations of captan fungicide. Results indicated that captan residue levels as low as one-thousandth the standard field rate could be detected using spore germination as the predictor. Fitting of the logistic decline model to the data created a standard curve to allow quantitative estimation of fungicide residue based on observed level of spore germination. A modified version of the bioassay, which can be used to detect carbohydrate or nutrient sources on the fruit surface, was also demonstrated.