Tebuconazole dissipation and metabolism in Tifton loamy sand during laboratory incubation

Authors: Strickland, Timothy - Tim; Potter, Thomas; JOO, HYUN - UNIV OF FLORIDA

Submitted to: Pest Management Science
Publication Type: Peer Reviewed Journal
Publication Acceptance Date: 12/9/2003
Publication Date: 3/12/2004
Citation: Strickland, T.C., Potter, T.L., Joo, H. 2004. Tebuconazole dissipation and metabolism in Tifton loamy sand during laboratory incubation. Pest Management Science. Pest Management Science. 60:703-709.

Interpretive Summary: Pest and disease pressure are high in the warm and humid southern coastal plain. Maintaining economically viable agricultural enterprise in this region requires regular application of agricultural chemicals to minimize crop loss. This scenario is expected to continue for the foreseeable future. However, chemicals are needed that are effective at controlling the pest or disease problem of concern, but that have minimal impact on non-target organisms (including humans). Preference would also be for chemicals that are effective for a targeted window of time, but that are readily degraded to harmless compounds in the natural environment. It is therefore critical that we understand how pesticides effect and are effected by biological and environmental conditions. Here, we report the results of a laboratory study to determine the degradation rate of the fungicide tebuconazole. Using soil from south Georgia, we found that the effective time to 50% dissipation for this compound ranges from 41-46 days. We also found that, even though tebuconazole is used to control fungal diseases, it does not appear to have any harmful effects on the activity rates of normal soil microflora when used at the recommended application rate. We also noted temporal accumulation of selected metabolites and are conducting further studies to determine the rate at which these compounds degrade.

Technical Abstract: The triazole fungicide, tebuconazole, is widely used to control soil borne and foliar diseases in peanuts and many other crops. No published data are currently available on the extent and rate at which this compound degrades in soil under conditions of use in the Atlantic Coastal Plain region of Georgia. This region is the center of U.S. peanut production and products containing tebuconazole are applied to an estimated 40% of the peanut acreage in the region. We conducted a laboratory incubation to evaluate the potential for tebuconazole to degrade in a Tifton sandy loam with and without poultry litter amendments and to determine the effect this fungicide may have on soil microbial activity. Results indicated a lag of approximately 21 days before degradation was initiated. This was followed by a consistent decline in tebuconazole concentration to day 63 when incubations were terminated. In the unamended control, 27%, and in the litter amended, 59% of the parent compound remained. Based on these data, the times to 50% dissipation were 41 and 46 days for the unamended and litter amended soils, respectively. Four degradates were identified in soil extracts at the end of the incubations. On a molar basis they accounted for 53% of the parent compound added to the unamended soil. Only one degradate was identified in the litter amended soil and it accounted for only 1.4% of the added tebuconazole. Tebuconazole had no effect on microbial activity as measured by changes in microbial biomass or respiration, however, the onset of degradation followed a substantial reduction in microbial respiration. It is suggested that an induction period is necessary before soil microflora degrade the compound and that the length of the induction period may be determined by the availability of more readily degradable carbon substrates. Addition of poultry litter to the soil greatly increased net respiration, however it decreased tebuconazole's degradation rate.