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United States Department of Agriculture

Agricultural Research Service

Research Project: SOIL RESPONSE TO CONSERVATION TILLAGE IN A COTTON-PEANUT ROTATION Title: Fungicide Dissipation and Impact on Metolachlor Aerobic Soil Degradation and Soil Microbial Dynamics

Authors
item White, Paul
item Potter, Thomas
item Culbreath, Albert -

Submitted to: Science of the Total Environment
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: November 8, 2009
Publication Date: February 15, 2010
Citation: White Jr, P.M., Potter, T.L., Culbreath, A.K. 2010. Fungicide Dissipation and Impact on Metolachlor Aerobic Soil Degradation and Soil Microbial Dynamics. Science of the Total Environment. 408(6):1393-1402.

Interpretive Summary: Pesticides are typically applied as mixtures and or sequentially to soil during crop production. A common scenario is herbicide application at planting followed by sequential fungicide applications post-emergence. Fungicides depending on their spectrum of activity may alter and impact soil microbial communities thus there is a potential to impact soil processes responsible for herbicide degradation. This may change herbicide efficacy and environmental fate characteristics. Our study objective was to determine the effects of 4 peanut fungicides, Bravo® WeatherStik 720F (chlorothalonil), Folicur® 3.6 F (tebuconazole), Topguard® 1.04 DC (flutriafol), and Alto® 100 SL (cyproconazole) on the dissipation kinetics of the herbicide, metolachlor (Dual Magnum ®). This was done through laboratory incubation of field treated soil. Chlorothalonil significantly reduced metolachlor loss as compared to the non-treated control or soil treated with the other fungicides. The time needed for 50% metolachlor loss was 116 d in soil treated with chlorothalonil, as compared to 45, 53, and 46 days for the remaining fungicides. Reductions were observed for metolachlor metabolites in the chlorothalonil-treated soil. This suggested that the fungicide impacted the soil’s ability to degrade metolachlor. Fungicide half-lives were 28 to 80 days. Overall study results indicated that chlorothalonil has the potential to substantially increase soil persistence (2-fold) of metolachlor and alter fate and transport processes.

Technical Abstract: Pesticides are typically applied as mixtures and or sequentially to soil during crop production. A common scenario is herbicide application at planting followed by sequential fungicide applications post-emergence. Fungicides depending on their spectrum of activity may alter and impact soil microbial communities thus there is a potential to impact soil processes responsible for herbicide degradation. This may change herbicide efficacy and environmental fate characteristics. Our study objective was to determine the effects of 4 peanut fungicides, chlorothalonil (2,4,5,6-tetrachloro-1,3-benzenedicarbonitrile), tebuconazole (a-[2-(4-chlorophenyl)ethyl]-a-(1,1-dimethylethyl)-1H-1,2,4-triazole-1-ethanol), flutriafol (a-(2-fluorophenyl)-a-(4-fluorophenyl)-1H-1,2,4-triazole-1-ethanol), and cyproconazole (a-(4-chlorophenyl)-a-(1-cyclopropylethyl)-1H-1,2,4-triazole-1-ethanol) on the dissipation kinetics of the herbicide, metolachlor (2-chloro-N-(6-ethyl-o-tolyl)-N-[(1RS)-2-methoxy-1-methylethyl]acetamide), and on the soil microbial community. This was done through laboratory incubation of field treated soil. Chlorothalonil significantly reduced metolachlor soil dissipation as compared to the non-treated control or soil treated with the other fungicides. Metolachlor DT50 was 116 d for chlorothalonil-treated soil and 56, 45, 53, and 46 d for control, tebuconazole, flutriafol, and cyproconazole-treated soils, respectively. Significant reductions in predominant metolachlor metabolites, metolachlor ethane sulfonic acid (MESA) and metolachlor oxanilic acid (MOA), produced by oxidation of glutathione-metolachlor conjugates were also observed in chlorothalonil treated soil. This suggested that the fungicide impacted soil glutathione-S-transferase (GST) activity. Fungicide DT50 were 27-80 d but impacts on the soil microbial community as indicated lipid biomarker analysis was minimal. Overall study results indicated that chlorothalonil has the potential to substantially increase soil persistence (2-fold) of metolachlor and alter fate and transport processes. GST mediated metabolism is common pesticide detoxification process in soil; thus there implications for the fate of many active ingredients.

Last Modified: 12/19/2014
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