Degradation of Metalaxyl and Mefenoxam and Effects on the Microbiological Properties of Tropical and Temperate Soils

Abstract

The degradation of various formulations of the racemic mixture and the enantiomers (including mefenoxam) of metalaxyl in typical soils from Germany and Cameroon in controlled incubation experiments was studied. The kinetics of the degradation or transformation was determined by means of reversed phase HPLC, while the enantiomeric ratios were measured by HPLC with a chiral Whelk O1 column. The dynamics of the quantitative changes in microbiological properties induced by the addition of these fungicides at their recommended field rates were determined in the soils during a 120-day incubation experiment. The degradation followed first-order kinetics (R2≥0.96). Higher metalaxyl acid metabolite concentrations were found in German than in Cameroonian soils. The enantiomers of the fungicide had different degradation rates in both soils, with half-lives ranging from 17 to 38 days. All forms of metalaxyl had lower degradation rates in the Cameroonian soil than in the German soil. The degradation of the R-enantiomer was much faster than the S-enantiomer in the German soil and slower than the S-enantiomer in the Cameroonian soil, suggesting that different microbial populations, which may be using different enzymes, have different degradation preferences. The type of soil significantly influenced the effect of these fungicides on the soil parameters studied. Incorporation of these fungicides resulted in a change in the ecophysiological status of the soil microbial community as expressed by microbial activities. The activity of phosphatases and β-glucosidase, the mineralization and availability of N and most plant nutrients in soils were stimulated, whereas the activity of dehydrogenase and the availability of NO3−, were generally adversely affected. The soil NH4+, NO3−, and enzymes activities values in general did not correlate with the degradation of metalaxyl in both soils. However, the degradation of formulated and unformulated metalaxyl was positively correlated to the activity of acid phosphatase in the German soil (R2, 0.84 and 0.94 respectively) and in the Cameroonian soil (R2, 0.97 and 0.96 respectively).

Use of Several Natural Products from Selected Nicotiana Species to Prevent Black Shank Disease in Tobacco

“…However, fungicides are not efficient for highly susceptible Burley varieties or for dark tobaccos (1). In addition, fungicides may have long-term deleterious effects such as acquired resistance, collateral toxicity, and environmental pollution (12,13). Because of the adverse effects of the fungicides, there is a need for alternative bio-chemicals, which are sustainable and ecofriendly.…”

Fungicide: Modes of Action and Possible Impact on Nontarget Microorganisms

“…PA fungicide applications can increase the prevalence of fungicide resistance in pathogen population and yield more fungicide-resistant isolates, as shown by a recent study using AFLP (amplified fragment length polymorphism) and SSR (simple sequence repeats) markers [69]. Fungicides in the PA group must be used with caution, as the side effect of this fungicide on N cycling associated bacteria was reported [33].…”

Effect of formulation and repeated applications on the enantioselectivity of metalaxyl dissipation and leaching in soil

“…For example, accelerated degradation after repeated pesticide applications and reduced leaching by the use of clay‐based formulations, compared with formulations containing the pesticide in an immediately available form, have been described . For chiral pesticides, research conducted on this subject does not generally account for individual enantiomers, implicitly assuming that the effects of such practices are identical for both enantiomers …”

“…21 -30 For chiral pesticides, research conducted on this subject does not generally account for individual enantiomers, implicitly assuming that the effects of such practices are identical for both enantiomers. 31,32 The main objective of this work was to address the question of whether repeated applications could affect the enantioselectivity of metalaxyl dissipation and leaching in soil. Water-dissolved metalaxyl and two novel clay-based formulations of the fungicide were used in the experiments further to address the effect of formulation on the enantioselectivity of metalaxyl dissipation and leaching patterns under single and repeated fungicide application regimes.…”